Emerging Infectious Diseases Volume 13 Issue 2

2007·5.5 MB·English

by  CDC

Peer-Reviewed Journal Tracking and Analyzing Disease Trends pages 191–364
EDITOR-IN-CHIEF
D. PeterDrotman
EDITORIALSTAFF EDITORIALBOARD
Founding Editor Dennis Alexander, Addlestone Surrey, United Kingdom
Joseph E. McDade, Rome, Georgia, USA Barry J. Beaty, Ft. Collins, Colorado, USA
Managing SeniorEditor Martin J. Blaser, New York, New York, USA
Polyxeni Potter, Atlanta, Georgia, USA David Brandling-Bennet, Washington, D.C., USA
Associate Editors Donald S. Burke, Baltimore, Maryland, USA
Paul Arguin, Atlanta, Georgia, USA Arturo Casadevall, New York, New York, USA
Charles Ben Beard, Ft. Collins, Colorado, USA Kenneth C. Castro, Atlanta, Georgia, USA
David Bell, Atlanta, Georgia, USA Thomas Cleary, Houston, Texas, USA
Jay C. Butler, Anchorage, Alaska, USA Anne DeGroot, Providence, Rhode Island, USA
Vincent Deubel, Shanghai, China
Charles H. Calisher, Ft. Collins, Colorado, USA
Paul V. Effler, Honolulu, Hawaii, USA
Stephanie James, Bethesda, Maryland, USA
Ed Eitzen, Washington, D.C., USA
Brian W.J. Mahy, Atlanta, Georgia, USA
Duane J. Gubler, Honolulu, Hawaii, USA
Nina Marano, Atlanta, Georgia, USA
Richard L. Guerrant, Charlottesville, Virginia, USA
Martin I. Meltzer, Atlanta, Georgia, USA
Scott Halstead, Arlington, Virginia, USA
David Morens, Bethesda, Maryland, USA David L. Heymann, Geneva, Switzerland
J. Glenn Morris, Baltimore, Maryland, USA Daniel B. Jernigan, Atlanta, Georgia, USA
Marguerite Pappaioanou, St. Paul, Minnesota, USA Charles King, Cleveland, Ohio, USA
Tanja Popovic, Atlanta, Georgia, USA Keith Klugman, Atlanta, Georgia, USA
Patricia M. Quinlisk, Des Moines, Iowa, USA Takeshi Kurata, Tokyo, Japan
Jocelyn A. Rankin, Atlanta, Georgia, USA S.K. Lam, Kuala Lumpur, Malaysia
Didier Raoult, Marseilles, France Bruce R. Levin, Atlanta, Georgia, USA
Pierre Rollin, Atlanta, Georgia, USA Myron Levine, Baltimore, Maryland, USA
Stuart Levy, Boston, Massachusetts, USA
David Walker, Galveston, Texas, USA
John S. MacKenzie, Perth, Australia
David Warnock, Atlanta, Georgia, USA
Marian McDonald, Atlanta, Georgia, USA
J. Todd Weber, Atlanta, Georgia, USA
John E. McGowan, Jr., Atlanta, Georgia, USA
Henrik C. Wegener, Copenhagen, Denmark
Tom Marrie, Edmonton, Alberta, Canada
Copy Editors
Ban Mishu-Allos, Nashville, Tennessee, USA
Thomas Gryczan, Anne Mather, Shannon O’Connor, Philip P. Mortimer, London, United Kingdom
Carol Snarey, P. Lynne Stockton Fred A. Murphy, Galveston, Texas, USA
Production Barbara E. Murray, Houston, Texas, USA
Reginald Tucker, Ann Jordan, Maureen Marshall P. Keith Murray, Geelong, Australia
Editorial Assistant Patrice Nordmann, Paris, France
Susanne Justice Stephen Ostroff, Honolulu, Hawaii, USA
David H. Persing, Seattle, Washington, USA
www.cdc.gov/eid Richard Platt, Boston, Massachusetts, USA
Gabriel Rabinovich, Buenos Aires, Argentina
Mario Raviglione, Geneva, Switzerland
Emerging Infectious Diseases
Emerging Infectious Diseases is published monthly by the Leslie Real, Atlanta, Georgia, USA
National Center for Infectious Diseases, Centers for Disease David Relman, Palo Alto, California, USA
Control and Prevention, 1600 Clifton Road, Mailstop D61, Nancy Rosenstein, Atlanta, Georgia, USA
Atlanta, GA30333, USA. Telephone [phone], Connie Schmaljohn, Frederick, Maryland, USA
fax [phone], email [email protected]. Tom Schwan, Hamilton, Montana, USA
Ira Schwartz, Valhalla, New York, USA
The opinions expressed by authors contributing to this journal
David Sencer, Atlanta, Georgia, USA
do not necessarily reflect the opinions of the Centers for Disease
Tom Shinnick, Atlanta, Georgia, USA
Control and Prevention or the institutions with which the authors
are affiliated. Bonnie Smoak, Bethesda, Maryland, USA
Rosemary Soave, New York, New York, USA
All material published in Emerging Infectious Diseases is in Frank Sorvillo, Los Angeles, California, USA
the public domain and may be used and reprinted without special P. Frederick Sparling, Chapel Hill, North Carolina, USA
permission; proper citation, however, is required.
Robert Swanepoel, Johannesburg, South Africa
Use of trade names is for identification only and does not Phillip Tarr, St. Louis, Missouri, USA
imply endorsement by the Public Health Service or by the U.S. Timothy Tucker, Cape Town, South Africa
Department of Health and Human Services. Elaine Tuomanen, Memphis, Tennessee, USA
John Ward, Atlanta, Georgia, USA
∞ Emerging Infectious Diseases is printed on acid-free paper that meets
Mary E. Wilson, Cambridge, Massachusetts, USA
the requirements of ANSI/NISO 239.48-1992 (Permanence of Paper)
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007
February 2007
On the Cover Deaths from Cysticercosis,
United States . . . . . . . . . . . . . . . . . . . . . .230
Hale Aspacio Woodruff (1900–1980)
F.J. Sorvillo et al.
The Art of the Negro: Interchange (1950–1951)
Oil on canvas (360 cm ×360 cm) Most deaths occur among Latino immigrants;
US-born persons are affected to a lesser extent.
Clark Atlanta University Collection of
African-American Art,
Community-associated
Atlanta, Georgia, USA
Methicillin-resistant Staphylococcus
aureusIsolates Causing Healthcare-
associated Infections . . . . . . . . . . . . . . .236
About the Cover p. 357 C.L. Maree et al.
MRSAisolates phenotypically similar to community-
associated strains have become the predominant
Synopsis
isolates associated with healthcare-associated
MRSAin our hospital.
Prevention of Immune
Cell Apoptosis . . . . . . . . . . . . . . . . . . . . .191 p. 193 Subclinical Avian Influenza A
J. Parrino et al. (H5N1) Infection in Cats . . . . . . . . . . . . .243
Lymphocyte apoptosis prevention may improve
M. Leschnik et al.
survival.
Infection without disease may occur under natural
conditions after contact with infected birds.
Research
Human African Trypanosomiasis,
Reduced Efficacy of Treated
Rural Democratic Republic
Nets and Residual Spraying for
of Congo . . . . . . . . . . . . . . . . . . . . . . . . . .248
Malaria Control, Benin . . . . . . . . . . . . . .199
P. Lutumba et al.
R. N’Guessan et al.
HATplaces a substantial economic hardship on
These tools may no longer be effective for malaria affected households.
control in parts of Benin.
Methicillin-resistant Staphylococcus
Code-based Syndromic Surveillance
aureusMultilocus Sequence Type
for Influenzalike Illness by
ST398, Central Europe . . . . . . . . . . . . . .255
International Classification of
W. Witte et al.
Diseases, Ninth Revision . . . . . . . . . . . .207
Isolates found in persons and animals in Germany
N. Marsden-Haug et al.
and Austria show a genetic relationship.
ICD-9 codes collected automatically in a syndromic
system are sensitive and specific in detecting
CampylobacterAntimicrobial Drug
outbreaks caused by respiratory viruses.
Resistance among Humans, Broiler
Imported Infectious Disease and Chickens, and Pigs, France . . . . . . . . . .259
Purpose of Travel, Switzerland . . . . . . .217 A. Gallay et al.
L. Fenner et al. Increasing quinolone resistance in human
Travelers who visited friends or relatives were more Campylobacterisolates and similar patterns in
likely to receive a diagnosis of malaria or viral broilers and humans suggest that quinolone use in
hepatitis than those who traveled for other reasons. broilers should be limited.
Invasive Group B Streptococcal Host-associated Genetic Import in
Infection in Infants, Malawi . . . . . . . . . . .223 Campylobacter jejuni . . . . . . . . . . . . . . .267
K.J. Gray et al. N.D. McCarthy et al.
p. 332
Incidence and serotype distribution of disease in C. jejunigenomes have a host signature that
Malawi are similar to those reported from industrial- enables attribution of isolates to animal sources.
ized countries, but case-fatality rate is high.
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007
Meningococcal Disease in
South Africa, 1999–2002 . . . . . . . . . . . . .273
G.B. Coulson et al.
February 2007
Serogroups and strains differ by location, although
hypervirulent strains were identified throughout the 329 Mycobacteria as Environmental
country. Portent in Chesapeake Bay Fish
Species
Neutralizing Antibodies after A.S. Kane et al.
Infection with Dengue 1 Virus . . . . . . . .282
332 Yersinia pestisin Remains of
M.G. Guzman et al. p. 335
Ancient Plague Patients
Severity of disease is markedly increased when
infection with dengue virus type 2 follows infection M. Drancourt et al.
with dengue virus type 1 by an interval of 20 years.
334 Rickettsia parkeriInfection after
Tick Bite, Virginia
Dispatches T.J. Whitman et al.
287 Waterborne Toxoplasmosis, Another Dimension
Northeastern Brazil
J. Heukelbach et al.
337 Mal de Mayo
290 Avian Influenza Risk Perception, R.T. Foster, Sr.
Europe and Asia
O. de Zwart et al. Letters
294 No Evidence of Avian Influenza A
(H5N1) among Returning US 341 Compensation for Avian Influenza
Travelers Cleanup
J.R. Ortiz et al.
342 Frog Virus 3, Cultured American
298 Postpartum Mastitis and Bullfrogs
Community-acquired Methicillin-
344 Pandemic Influenza School
resistant Staphylococcus aureus
Closure Policies
P. Reddy et al.
302 Herpes Simplex Virus Infection 345 Symptomatic Human Hantavirus
A. Knezevic et al. in the Americas
305 West Nile Virus Surveillance in 346 Echinococcosis Risk among
Clinic-admitted Raptors, Colorado Domestic Definitive Hosts, Japan
N. Nemeth et al.
347 Maculopathy and Dengue
308 Mosquitoborne Infections after
348 Enterohemorrhagic Escherichia
Hurricane Jeanne, Haiti, 2004
coliExcretion by Child and Her Cat
M.E. Beatty et al.
p. 337
349 Misdiagnosing Melioidosis
311 Characteristics of Staphylococcus
aureusInfections, Chicago 351 Subclinical Plasmodium
Pediatric Hospital falciparumInfection and HIV-1
P. Jaggi et al. Viral Load
315 Ertapenem Resistance of 353 African Tickbite Fever in Travelers,
Escherichia coli Swaziland
M.F. Lartigue et al.
355 Catheter-related Bacteremia and
318 Surveillance for Shiga Toxin–
Multidrug-resistant Acinetobacter
producing Escherichia coli,
lwoffii
Michigan, 2001–2005
S.D. Manning et al.
322 Rapid Genome Sequencing of News & Notes
RNAViruses
T. Mizutani et al.
About the Cover
325 PneumocystisPneumonia in HIV- 357 Microbiologic and Cultural
positive Adults, Malawi Interchange
J.J.G. van Oosterhout et al.
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007
Prevention of Immune Cell
Apoptosis as Potential Therapeutic
Strategy for Severe Infections
Janie Parrino,* Richard S. Hotchkiss,† and Mike Bray*
Some labile cell types whose numbers are normally or all severe infections that could be targets for pharmaco-
controlled through programmed cell death are subject to logic intervention. Such generic therapies could supple-
markedly increased destruction during some severe infec- ment agent-specific treatment by increasing resistance to
tions. Lymphocytes, in particular, undergo massive and
infection, potentially improving outcomes for patients in a
apparently unregulated apoptosis in human patients and
variety of disease states.
laboratory animals with sepsis, potentially playing a major
One physiologic process that characterizes some
role in the severe immunosuppression that characterizes
severe infections is a massive loss of lymphocytes, den-
the terminal phase of fatal illness. Extensive lymphocyte
apoptosis has also occurred in humans and animals infect- dritic cells, gastrointestial epithelial cells, and other cell
ed with several exotic agents, including Bacillus anthracis, types through apoptosis, or programmed cell death. This
the cause of anthrax; Yersinia pestis, the cause of plague; process is an apparent acceleration or dysregulation of the
and Ebola virus. Prevention of lymphocyte apoptosis, same process by which these cell populations are regulat-
through either genetic modification of the host or treatment ed during normal health (1,2). By impairing the develop-
with specific inhibitors, markedly improves survival in
ment of adaptive immune responses needed for recovery,
murine sepsis models. These findings suggest that inter-
the apoptotic destruction of lymphocytes and dendritic
ventions aimed at reducing the extent of immune cell apop-
cells could have a particularly adverse effect on disease
tosis could improve outcomes for a variety of severe
outcome. Fortunately, because programmed cell death is
human infections, including those caused by emerging
pathogens and bioterrorism agents. an orderly biochemical process triggered by specific stim-
uli and executed by a limited range of enzymes, it could be
inhibited through pharmacologic countermeasures, offer-
Despite success in controlling many infectious dis-
ing a novel approach to therapy.
eases, efforts to defend against the wide range of
We begin this article by summarizing evidence that a
microbes that threaten human health continue to be chal-
massive apoptotic loss of lymphocytes takes place in
lenged by the unexpected emergence of novel pathogens
humans during the course of septic shock and describing
and possible use of a variety of virulent agents as bio-
similar findings in animal models of sepsis. Data are then
logical weapons. A defensive strategy based solely on
presented that indicate that a marked die-off of lympho-
developing new vaccines and antimicrobial and antiviral
cytes also occurs in Ebola hemorrhagic fever, anthrax, and
drugs, each specific for only 1 or a few agents, is unlikely
plague, which suggests that unregulated apoptosis of these
to be successful in dealing with potential microbial threats
cells is a component of many, and perhaps all, severe
and will be exceedingly expensive. An alternative
infectious processes and may contribute to high case fatal-
approach attempts to identify mechanisms shared by most
ity rates by impairing adaptive immune function. After
describing encouraging results obtained in proof-of-con-
cept tests of antiapoptotic interventions in lethal murine
*National Institutes of Health, Bethesda, Maryland, USA; and
models of sepsis, we note some potential limitations of
†Washington University School of Medicine, Saint Louis, Missouri,
such therapy that could slow its introduction into the
USA
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007 191
SYNOPSIS
therapeutic regimen. Whatever the potential role of such that tip the balance toward or away from programmed cell
strategies, improved understanding of the causes, time death. These include members of the Bcl-2 protein family,
course, and extent of programmed cell death will aid man- which have both proapoptotic and antiapoptotic activity
agement of patients with severe infections. (Bcl-2 is antiapoptotic), and other inhibitors (Figure 1).
Despite these elaborate control mechanisms, innate or
Mechanism and Regulation of Apoptosis acquired defects in the control of apoptosis may lead to a
Apoptosis, or programmed cell death, is the method variety of disease states. For example, excessive inhibition
by which tissue remodeling takes place during normal of apoptosis is an underlying mechanism of cancer, while
growth and development and the physiologic mechanism an inappropriate increase is seen in some neurodegenera-
by which labile cell populations such as gastrointestinal tive diseases and other conditions.
epithelial cells, lymphocytes, dendritic cells, and neu-
trophils are regulated. Apoptosis is of particular impor- Lymphocyte Apoptosis in Sepsis
tance for the immune system as the means by which During normal health, the immediate fate of each lym-
self-recognizing lymphocytes are deleted and expanded phocyte is determined through continuous summation of a
lymphocyte populations are reduced at the conclusion of stream of proapoptotic and antiapoptotic signals that arrive
an acute immune response (3). This closely regulated, from its external environment and from its internal cyto-
energy-requiring process can be initiated through 2 differ- plasmic milieu. A shift toward initiation of apoptosis
ent mechanisms, each based on the successive activation should therefore be expected during the early phase of sep-
of preexisting but dormant cysteine-aspartate proteases, or sis, when bacteria or their byproducts stimulate
caspases (Figure 1). macrophages to release proapoptotic substances such as
As its name implies, the intrinsic apoptotic pathway TNF-α, nitric oxide, and glucocorticoids. As the disease
begins within the cell, when toxic alterations bring about a develops, accumulating products of lymphocyte apoptosis
decrease in mitochondrial transmembrane potential, lead- can act as antiinflammatory stimuli, which contribute
ing to the opening of mitochondrial membrane pores and
the release of cytochrome C and other substances into the
cytoplasm. The extrinsic pathway, by contrast, is triggered
by extracellular events through the binding to cell surface
receptors of tumor necrosis factor (TNF) superfamily
death ligands, including TNF-α and Fas ligand. Although
the intrinsic pathway involves early activation of caspase-
9, and the extrinsic pathway is mediated through caspase-
8, both lead to activation of the “executioner” caspase-3
and a variety of proteases and endonucleases. Once begun,
apoptosis may be described as an orderly disassembly of
the cell from within. Chromosomal DNA is cleaved into
oligonucleosomal segments, the nucleus is divided into
discrete subunits, and the cell itself is partitioned into mul-
tiple membrane-bound fragments whose outer surfaces are
marked by large numbers of phosphatidylserine molecules,
leading to their rapid uptake by phagocytes. Because all Figure 1. Apoptotic pathways of cell death. The extrinsic pathway
multicellular organisms use programmed cell death to is mediated by a variety of death receptor ligands, including tumor
necrosis factor (TNF) and Fas ligand (FasL), that trigger apoptosis
maintain and modify their tissues, this process does not
by binding to cell surface receptors. In the intrinsic pathway, sev-
evoke an inflammatory response, and its end products
eral adverse factors act upon mitochondria to cause loss of the
actually serve as antiinflammatory stimuli. Apoptosis thus mitochondrial membrane potential, resulting in leakage into the
differs markedly from necrosis, the chaotic breakdown cytosol of cytochrome C (Cyto C), which together with apoptotic
resulting from trauma and other types of damage, in its protease activating factor 1 forms the apoptosome that activates
caspase-9. Communication between the pathways exists through
morphologic and immunologic features (Table 1).
cleavage of Bcl-2 interacting domain (Bid) by active caspase-8 to
Necrosis is characterized by the early loss of outer mem-
form truncated Bid (tBid). Inhibitors of apoptosis (IAPs) can pre-
brane function, rapid cytoplasmic swelling and disintegra- vent caspase activation under certain conditions. Trail, tumor
tion, and release of cell contents into surrounding tissues, necrosis factor-α–related apoptosis-inducing ligand; Bim/Puma,
which evoke an intense inflammatory response. Bcl-2 interacting mediator of cell death/p53-upregulated modulator
of apoptosis; FADD, Fas-associated death domain; FLIP, Fas-
Alarge number of cell-surface and cytoplasmic pro-
associated death domain-like interleukin-1 converting enzyme-
teins participate in the detection and processing of signals
like inhibitory protein.
192 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007
Prevention of Immune Cell Apoptosis
to the immunosuppression commonly observed as sepsis because prolactin up-regulates expression of the antiapop-
progresses to septic shock, and which can lead to a state of totic protein Bcl-2. A third study also noted a profound
immune paralysis before death (2,3). loss of B and Tcells in the spleens of neonates who died
Numerous studies have demonstrated a massive apop- of sepsis and chorioamnionitis. Another study compared
totic loss of lymphocytes during sepsis. A prospective premortem blood counts in patients with septic shock, sep-
investigation in adult patients compared spleens obtained sis without shock, or nonseptic critical illness and found
either intraoperatively or within 6 hours after death from that increased lymphocyte apoptosis began early in septic
sepsis or trauma and found that those from sepsis patients shock, and that severe lymphopenia was predictive of a
showed a marked decrease in B cells and CD4 T cells fatal outcome (6,7).
(Figure 2) (1). The degree of splenic B-cell depletion cor- Extensive loss of lymphocytes through programmed
responded with the duration of sepsis. Active caspase-9 cell death has also been demonstrated in animal models of
was present in splenic lymphocytes with apoptotic fea- lethal sepsis induced either by normal intestinal flora or by
tures, suggesting a mitochondrial-mediated pathway of specific gram-negative bacteria. Studies using cecal liga-
cell death, although evidence indicates that apoptotic cell tion and perforation (CLP) in mice have shown profound
death in patients with sepsis can also proceed by the death lymphocyte apoptosis in multiple organs, including the
receptor pathway (4). In most patients, loss of cells from thymus and spleen (8). Massive lymphoid apoptosis in the
the spleen corresponded with a premortem decrease in cir- spleen and lymph nodes was also observed in baboons that
culating lymphocytes. developed fatal septic shock after injection of Escherichia
These findings were closely paralleled in another coli(9).
postmortem study, which showed that B and T cells and
dendritic cells were markedly depleted in lymphoid organs Lymphocyte Apoptosis in Ebola
of children dying of sepsis and that >3% of cells exhibit- Hemorrhagic Fever
ed histologic signs of apopotosis (5). Approximately 15% In addition to occurring during common forms of sep-
of patients had prolonged lymphopenia during their termi- sis, a marked increase in lymphocyte apoptosis has been
nal course. This report suggested a possible stimulus for observed in such exotic illnesses as Ebola hemorrhagic
apoptosis, in the form of persistent hypoprolactinemia, fever. When transferred to humans from an unidentified
Figure 2. Immunohistochemical identification
of B cells and follicular dendritic cells in
spleens of patients dying of trauma or sepsis.
Total B cells are decreased in the spleen of a
patient with sepsis (B) compared with that of
a trauma patient (A) (magnification ×400).
Similarly, follicular dendritic cells are
decreased in the spleen of a patient with sep-
sis (D) compared with that of a trauma patient
(C) (magnification ×600).
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007 193
SYNOPSIS
animal reservoir, Ebola virus replicates rapidly in ated lymphocyte apoptosis contributes to this process, but
macrophages and dendritic cells, causing intense inflam- a review of autopsy findings from 41 known cases of
mation, high viremia, and spread of infection to multiple inhalational anthrax in a 1979 outbreak in Sverdlorsk,
organs, with fever, coagulation abnormalities, and shock Russia, showed massive lymphocytolysis in mediastinal
(10). Case fatality rates have reached 90% in outbreaks in lymph nodes and spleens that was morphologically consis-
central Africa. tent with apoptosis (17).
Limited data from patients and more extensive data Experimental evidence shows that lethal toxin (LT),
from laboratory animals indicate that massive lymphocyte an important virulence factor encoded by B. anthracis,
apoptosis occurs during Ebola hemorrhagic fever and may interferes with intracellular signaling and can induce apop-
contribute to the high death rate. Thus, the few patients tosis. Ultrastructural analysis and terminal deoxynu-
who survive infection develop antibodies to the virus dur- cleotidyl (TUNEL) staining of LT-treated human
ing the second week of illness, while fatally infected per- monocyte–derived dendritic cells found activation of
sons apparently undergo terminal immunosuppression apoptotic pathways (18). The same authors demonstrated
similar to that seen with septic shock (11,12). A small that bone marrow dendritic cells from C57BL/6 and
study of blood samples from patients in Gabon showed BALB/c mice differed in susceptibility to LT: cells derived
that fatal cases of Ebola hemorrhagic fever were character- from C57BL/6 mice underwent apoptosis and LT caused
ized by extensive intravascular apoptosis, particularly of T necrosis of equivalent cells from BALB/c mice.
cells, beginning at least 5 days before death, with a
decrease and eventual disappearance of Bcl-2 mRNA Lymphocyte Apoptosis in Plague
expression (11). In survivors, by contrast, Bcl-2 mRNA The gram-negative bacillus Yersinia pestis causes 2
was identified in circulating cells during T-cell activation. principal forms of illness in humans, a localized infection
Importantly, a similar loss of Bcl-2 has been reported in of lymph nodes (bubonic plague) and a highly lethal sep-
circulating lymphocytes of patients with sepsis (4). ticemia that is a particularly fulminant form of septic shock
Because of the difficulty of performing clinical (19). The striking virulence of Y. pestisin humans is attrib-
research under the conditions of an Ebola outbreak, the utable to a collection of outer membrane proteins (Yops)
pathogenesis of lethal infection has been elucidated princi- that cause immune suppression and trigger apoptosis (20).
pally through intensive studies in nonhuman primates, Patients dying of plague would therefore be expected to
which develop uniformly lethal illness resembling fatal demonstrate increased lymphocyte apoptosis, but data to
hemorrhagic fever in humans. Lymphocytes in these ani- support this hypothesis are lacking. However, laboratory
mals remain free of viral infection but nevertheless under- studies using a murine model of intranasal Y. pestisinfec-
go extensive apoptosis, with early development of tion have provided evidence of increased lymphocyte
lymphopenia and depletion of circulating natural killer apoptosis in the spleen by 36 hours after infection (21) (R
cells and CD4+ and CD8+ lymphocytes (13). Massive Hotchkiss, V. Miller, unpub. data).
lymphocyte apoptosis is also observed histologically in YopH protein inhibits T cell activation by blocking
lymph nodes, spleen, and other lymphoid tissues, begin- early phosphorylation events necessary for signal trans-
ning by day 3 postinfection. Amodel of Ebola virus infec- duction through the antigen receptor (22). In tests with pri-
tion in mice has demonstrated extensive lymphocytolysis mary T cells or Jurkat T leukemia cells, the extended
in lymph nodes, spleen, and thymus, with histologic fea- presence of YopH led to apoptosis through a mitochondria-
tures suggestive of apoptosis (14). Lymphocyte apoptosis dependent pathway, as indicated by mitochondrial break-
has also been demonstrated in vitro in cultures of Ebola down, caspase activation, DNA fragmentation, and
virus–infected peripheral blood mononuclear cells, which annexin V binding. Cell death could be blocked through
suggests that infected monocytes release substances that coexpression of Bcl-x , an antiapoptotic protein in the Bcl-
L
induce apoptosis in neighboring lymphocytes (15). 2 family, or by treatment with caspase inhibitors. Evidence
of induction of apoptosis was also found in a plague model
Lymphocyte Apoptosis in Anthrax in rats, in which increased numbers of caspase-positive
In inhalational anthrax, spores of Bacillus anthracis cells were noted in lymph nodes 36 hours after infection,
are carried by pulmonary macrophages to mediastinal most prominently in nodes containing the greatest number
lymph nodes, where their replication results in local tissue of bacteria, which suggests Yop-mediated apoptosis (23).
injury, bacteremia, shock, and death (16). The ability of the However, the apoptotic cells could not be identified
organism to cause rapidly overwhelming infection sug- because of extensive tissue destruction. Multifocal lym-
gests that, as in the case of Ebola hemorrhagic fever, phocytolysis was also observed in the white pulp of the
immunosuppression plays a role in lethal illness. Few data spleen, with resultant loss of periarteriolar lymphoid
are available from human cases to assess whether acceler- sheath–associated lymphocytes.
194 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007
Prevention of Immune Cell Apoptosis
Experimental Inhibition of Apoptosis
Efforts to prevent excessive lymphocyte apoptosis
during severe infection have focused either on modifica-
tion of the signal processing system to create an inherent
bias against the triggering of cell death pathways or on
inhibition of caspase activity to block their execution.
Proof-of-concept experiments with murine sepsis models
have shown that both approaches can improve survival.
Several studies have shown that transgenic mice overex-
pressing the antiapoptotic protein Bcl-2 were completely
protected against lymphocyte apoptosis in Tcells and par-
tially protected in B cells after CLP and showed an
increase in survival (24,25). The exact protective mecha-
nisms, however, are unclear. The authors of 1 report
argued that the beneficial effect of Bcl-2 did not depend
on prevention of lymphocyte apoptosis because adoptive
transfer of myeloid cells overexpressing Bcl-2 also result-
ed in improved survival after CLP of Rag-1−/− mice,
which lack mature T and B cells (25). This finding sug-
gests that protection resulted from the release of cytopro-
tective or antiinflammatory molecules from Bcl-2-
overexpressing cells, from an increase in neutrophils at
sites of infection, or both. Despite these findings, recent
studies that showed a lower death rate after CLPin trans-
genic mice expressing the antiapoptotic protein Akt in T
cells have added further support to the concept that pre-
vention of lymphocyte apoptosis is an independent sur-
vival factor in sepsis (26).
In addition to these reports that used the CLPmodel,
preliminary studies have shown that Bcl-2 overexpression
Figure 3. Decreased apoptosis caused by overexpression of Bcl-2
prevents lymphocyte apoptosis in mice infected with Y.
protein in a mouse model of plague. Wild-type mice (A) and mice
pestis (R. Hotchkiss, unpub. data). Bcl-2 transgenic mice that overexpressed Bcl-2 in lymphocytes (B) were injected
that overexpressed Bcl-2 in T and B lymphocytes had a intranasally with Yersinia pestis. Thymuses were obtained at 72 h
marked decrease in apoptosis at 72 hours after Y. pestis postinfection and stained by using the terminal deoxynucleotidyl
(TUNEL) method as a marker of apoptotic cell death. Note the
infection compared with wild-type animals (Figure 3).
decrease in apoptotic cells in the thymus of the Bcl-2 transgenic
These findings provide hope that apoptotic cell death in mouse (magnification ×400).
plague may be preventable by a Bcl-2–based therapy.
Pharmacologic interventions have also been used to
prevent initiation of lymphocyte apoptosis in murine mod-
els of sepsis (Table 2). One approach has aimed to block improves cardiac output, and lowers the serum level of the
initial triggering of the extrinsic pathway by preventing antiinflammatory cytokine interleukin-10 (27).
cellular synthesis of Fas or FasL or by administering an Another strategy aims to influence intracellular sig-
inhibitor of Fas-FasL binding. Both techniques have naling networks in a direction opposing the initiation of
shown benefit in murine CLPstudies. Preliminary studies programmed cell death. A recent publication by the
by Chung et al. demonstrated that mice genetically defi- Hotckhiss group showed that this could be achieved by
cient in FasLshowed better survival after CLPthan their exploiting the normal CD40 regulatory pathway through
wild-type counterparts (34), and a survival benefit was which lymphocytes are stimulated in an antiapoptotic
also observed when mice were treated with siRNAto block direction to produce clonal expansion and functional mat-
intracellular synthesis of Fas (28). Markedly improved sur- uration (30). Mice treated with a monoclonal antibody that
vival was also observed when a Fas receptor fusion protein binds to and stimulates the CD40 receptor showed up-reg-
was injected subcutaneously 12 hours after CLPto act as a ulation of the antiapoptotic protein Bcl-x , an absence of
L
decoy for FasLbinding. Detailed studies have shown that apoptosis of B cells, a decrease in loss of T cells, and a
this intervention restores normal immune function, resistance to CLP(29).
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007 195
SYNOPSIS
Efforts have also been made to alter intracellular sig- offer several advantages is targeted delivery of antiapop-
naling by introducing active portions of Bcl-x fused to totic molecules. Similar to current immune-based thera-
L
carrier peptides to facilitate its transport into cells. In a pies, apoptosis inhibitors could be directed to specific
murine CLP model, treatment resulted in a decrease in classes of immune cells, for example by conjugating them
lymphocyte apoptosis, but the effect was less marked than to antibodies to CD4 or CD20, thus avoiding adverse con-
that observed in transgenic animals constitutively express- sequences (35).
ing the same protein (30). Another approach has used the Other potential limitations of antiapoptotic therapy
licensed HIV protease inhibitors nelfinavir and ritonavir, relate to possible undesired effects of the use of caspase
which in addition to blocking the cleavage of HIVpropep- inhibitors. First, because only a small amount of activated
tides have direct antiapoptotic effects (31). The latter were caspase-3 is sufficient to initiate genomic DNAbreakdown
initially assumed to result from caspase inhibition, but fur- and lead to apoptotic cell death, a high degree of inhibition
ther studies showed that these drugs prevent initiation of would be needed to achieve therapeutic effectiveness (36).
the intrinsic apoptotic pathway by stabilizing the mito- This requirement presents a therapeutic challenge because
chondrial membrane potential. Oral administration of nel- of the need for persistent and nearly complete caspase
finavir and ritonavir to mice, beginning either before or 4 blockade. In addition, there is increasing recognition that
hours after CLP, resulted in decreased lymphocyte apopto- caspases have numerous functions in addition to their roles
sis and improved survival (31). Because both drugs are as mediators of programmed cell death. One subset of cas-
licensed for use in humans, this approach could potential- pases is critical for regulation of inflammation by process-
ly be evaluated in sepsis patients. ing proinflammatory cytokines such as interleukin-1β;
Efforts to prevent completion of the programmed cell others are essential for lymphocyte activation, prolifera-
death process by blocking executioner caspases have also tion, and protective immunity (37,38). Patients with
been reported. Studies with the broad-spectrum caspase defects in caspase-8, for example, are immunodeficient
inhibitor zVAD showed decreased apoptosis and improved and have recurring infections (39). Blocking caspases
survival in a mouse CLPmodel (32). Similarly, a selective might therefore have some beneficial effects in decreasing
caspase-3 inhibitor decreased blood bacterial counts and lymphocyte apoptosis in sepsis, but these could be coun-
improved survival in mice with sepsis (33). Treatment of terbalanced by adverse effects on the ability of the patient
septic Rag 1−/− mice with caspase inhibitors failed to to mount an effective immune response. Finally, that inhi-
improve survival, which suggests that the beneficial effect bition of caspases might induce hyperacute TNF-induced
required the presence of lymphocytes. shock in certain situations has been recently reported (40).
In view of the possible deleterious effects of using caspase
Potential Limitations of Antiapoptotic Therapy inhibitors to treat sepsis, therapy directed at a temporary
Although the proof-of-concept studies described inhibition of specific caspases, such as caspase-3 or cas-
above have shown promising results, deliberate inhibition pase-12, timed to either the hyperinflammatory phase or
of apoptosis during severe infections might have unexpect- the hypoinflammatory phase of sepsis, might be the most
ed and undesired consequences. One potential adverse effective approach.
effect of antiapoptotic therapy involves its effects on
pathogen replication. Some intracellular agents, such as Conclusions
poxviruses, actively inhibit apoptosis of their host cells so Amassive loss of lymphocytes and other cells through
as to permit their own continued replication. Theoretically, apoptosis is a proven component of the physiologic
pharmacologic inhibition of apoptosis in those situations changes that occur over the course of septic shock. This
could actually worsen the clinical outcome by providing an process appears also to occur in a variety of other severe
advantage to the pathogen. It may therefore be essential to infections, including anthrax, plague, and Ebola hemor-
identify the causative agent of infection before initiating rhagic fever, which are of major concern for biodefense. A
antiapoptotic therapy. An alternative approach that may variety of proof-of-concept studies with murine sepsis
196 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 2, February 2007