Published: 01 February 2000
Apoptosis Induced In Vitro and In Vivo During Infection by Ebola and Marburg Viruses

Thomas W Geisbert, Lisa E Hensley, Tammy R Gibb, Keith E Steele, Nancy K Jaax & Peter B Jahrling
Laboratory Investigation volume 80, pages171C186(2000)Cite this article

Pathology Division, US Army Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland

Induction of apoptosis has been documented during infection with a number of different viruses.

In this study, we used transmission electron microscopy (TEM) and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling to investigate the effects of Ebola and Marburg viruses on apoptosis of different cell populations during in vitro and in vivo infections.

Tissues from 18 filovirus-infected nonhuman primates killed in extremis were evaluated. Apoptotic lymphocytes were seen in all tissues examined. Filoviral replication occurred in cells of the mononuclear phagocyte system and other well-documented cellular targets by TEM and immunohistochemistry, but there was no evidence of replication in lymphocytes. With the exception of intracytoplasmic viral inclusions, filovirus-infected cells were morphologically normal or necrotic, but did not exhibit ultrastructural changes characteristic of apoptosis. In lymph nodes, filoviral antigen was co-localized with apoptotic lymphocytes. Examination of cell populations in lymph nodes showed increased numbers of macrophages and concomitant depletion of CD8+ T cells and plasma cells in filovirus-infected animals. This depletion was particularly striking in animals infected with the Zaire subtype of Ebola virus.

In addition, apoptosis was demonstrated in vitro in lymphocytes of filovirus-infected human peripheral blood mononuclear cells by TEM.

These findings suggest that lymphopenia and lymphoid depletion associated with filoviral infections result from lymphocyte apoptosis induced by a number of factors that may include release of various chemical mediators from filovirus-infected or activated cells, damage to the fibroblastic reticular cell conduit system, and possibly stimulation by a viral protein.

Apoptosis Induced In Vitro and In Vivo During Infection by Ebola and Marburg Viruses | Laboratory Investigation

T Lymphocyte Apoptosis and Memory in Viral Infection: A Dissertation
By Enal Shahid Razvi

Acute viral infections in humans and mice induce T lymphocyte responses which mediate viral clearance and result in the establishment of immunological memory.

The course of an immune response to acute viral infection is associated with an immune deficiency in the lymphocyte compartment. This is usually characterized by the inability of lymphocytes to productively respond to mitogen or recall antigen.

This thesis examined the acute lymphocytic choriomeningitis virus (LCMV) infection of the mouse and showed that T lymphocytes isolated from acutely LCMV-infected mice underwent activation-induced apoptosis upon signalling through the T-cell receptor (TcR)-CD3 complex.

Kinetic studies demonstrated that this sensitivity to apoptosis directly correlated with the induction of immune deficiency, as measured by impaired proliferation in response to anti-CD3 antibody or to concanavalin A. Cell cycling in interleukin-2 (IL-2) alone stimulated proliferation of LCMV-induced T cells without inducing apoptosis, but preculturing of T cells from acutely-infected mice in IL-2 accelerated apoptosis upon subsequent TcR-CD3 crosslinking. T lymphocytes isolated from mice after the acute infection were less responsive to IL-2, but IL-2 receptor-bearing T cells, presumably memory T cells, responding to IL-2 were primed in each case to die a rapid apoptotic death upon TcR-CD3 crosslinking.

These results indicated that virus infection-induced unresponsiveness to T-cell mitogens is in part attributable to apoptosis of the activated lymphocytes and suggest that the sensitization of memory cells by IL-2 and other stimulatory cytokines induced during an acute infection will cause them to die upon antigen recognition, thereby impairing specific responses to nonviral (recall) antigens.

The cytotoxic T lymphocyte (CTL) response to acute LCMV infection is characterized by a massive (10-20 fold) expansion of CD8+ cell number, which after clearance of virus declines in number and returns to levels present prior to infection.

This thesis documents the presence of high levels of apoptotic lymphocytes in situ in the spleens of mice during the silencing of the immune response to acute LCMV infection. Apoptotic cells were detected by an in situ nucleotidyl transferase (ISNT) assay. Both T and B lymphocytes, as revealed by immunohistochemical analysis, are shown to be dying in vivo, the latter in clusters. A biphasic occurrence of apoptosis during the course of the acute infection was found, with an increase in numbers of apoptotic cells above background at day 3 post-infection, and at day 11 post-infection, a second more pronounced peak coincident with the decline of the CTL response to the infection and with the decrease in total spleen leukocyte number. Apoptosis in vivo was detected in lpr mice lacking Fas expression, a molecule involved in lymphocyte apoptosis. Fas expression thus may not be required for lymphocyte apoptosis in the context of an acute viral infection. Apoptosis in situ and the silencing of the CD8+ T lymphocyte response to acute LCMV infection were unaffected by the enforced lymphocyte-directed expression of Bcl-2, a protein blocking IL-2 deprivation-induced apoptosis of lymphocytes. Experiments aimed at addressing the role of Bcl-2-sensitive apoptotic pathways in the development of viral persistence revealed that high-dose infection of Bcl-2-transgenic mice results in death of the animals.

Flow cytometric analysis showed an accumulation of Thy1.2+ T cells in the lungs of these animals, and the air spaces in the lungs were occluded with cellular and fluid infiltrates. These results suggest that the pathology seen in the Bcl-2-transgenic mice upon high-dose infection is perhaps immune response-mediated (an immunopathology). This is consistent with a role for Bcl-2-sensitive pathways of lymphocyte apoptosis in the pathogenesis of persistent LCMV infection.

The in situ demonstration of apoptosis in spleens during infection provide direct in vivo evidence for the death of lymphocytes during the recovery from an acute viral infection. This indicates that apoptotic elimination of the population en masse is a mechanism for halting an antiviral immune response upon clearance of virus.

Furthermore, the data argue that IL-2 deprivation-driven apoptosis, upon clearance of virus, of the expanded T lymphocyte compartment is not the major mechanism involved in the silencing of the T cell response to acute LCMV infection.

Resolution of an acute immune response leads into the generation of longterm immunological memory. Since this thesis focussed on T cell responses in viral infection, it was important to characterize the in vivo state of memory CD8+ T cells. During acute LCMV infection, the majority of the LCMV-specific CTL activity tested immediately ex vivo was mediated by CD8+ L-selectin-Mac-1+ CTL. The L-selectin- population of CD8+ cells elicited during acute infection also carried \u3e99% of the restimulatable CD8+ CTLp to LCMV, and these required added IL-2 for development into effectors in vitro.

In contrast to the acute infection, most of the virus-specific CTLp in immune mice were L-selectin+. Examination of CD8+ T cells in LCMV-immune mice revealed that a L-selectin+ blast-sized population of cycling CD8+ cells contained CTLp which developed into effector CTL in the absence of added IL-2. These cells also expressed Mac-1 and IL-2R. Flow cytometric sorting for IL-2R+ and IL-2R-CD8+ cells in the immune animal revealed, by limiting dilution analysis, similar frequencies of CTLp in both populations. In bulk restimulation assays, the CD25+ CTLp did not require added IL-2 for their in vitro development into effectors, whereas the CD25- CTLp did.

Hence, the different requirements for CTLp to effector development in vitro reflect qualitative differences in the in vivo state of the CTLp in the various subpopulations. LCMV-specific memory CTLp not requiring added IL-2 for differentiation were also found in the small-sized, non-cycling, CD8+L-selectin- cells.

In contrast, the small-sized, non-cycling, CD8+L-selectin+, and CD8+IL-2R- populations also carried CTLp, but these required added IL-2 for development into effector CTL.

Hence, T cell memory to LCMV is distributed among various lymphocyte subpopulations in immune animals, and the presence of an activated cycling cell component may account for the stability and long-term perpetuation of antiviral immunological memory.

In summary, the susceptibility of activated T lymphocytes to apoptosis probably explains an aspect of virus-induced immune deficiency and allows for the establishment of homeostasis subsequent to the resolution of an acute viral infection

Topics: Apoptosis; Immunologic Memory; Infection; T-Lymphocytes; Academic Dissertations; Dissertations, UMMS, Life Sciences, Medicine and Health Sciences
Publisher: eScholarship@UMMS
Year: 1994
OAI identifier:
Provided by: eScholarship@UMMS

T Lymphocyte Apoptosis and Memory in Viral Infection: A Dissertation - CORE

Virus interactions with endocytic pathways in macrophages and dendritic cells
Jason Mercer
Urs F. Greber
Published:July 03, 2013


A wide range of viruses can successfully infect macrophages and dendritic cells (DCs).

Viruses manipulate pattern recognition receptors (PRRs) for entry as well as binding.

Does constitutive macropinocytosis provide a free ride for virus entry?

Viruses use diverse strategies to subvert destruction and detection by antigen-presenting cells (APCs).

Macrophages and dendritic cells (DCs) are at the front line of defence against fungi, bacteria, and viruses. Together with physical barriers, such as mucus and a range of antimicrobial compounds, they constitute a major part of the intrinsic and innate immune systems. They have elaborate features, including pattern recognition receptors (PRRs) and specialized endocytic mechanisms, cytokines and chemokines, and the ability to call on reserves. As masters of manipulation and counter-attack, viruses shunt intrinsic and innate recognition, enter immune cells, and spread from these cells throughout an organism. Here, we review mechanisms by which viruses subvert endocytic and pathogen-sensing functions of macrophages and DCs, while highlighting possible strategic advantages of infecting cells normally tuned into pathogen destruction.

Virus interactions with endocytic pathways in macrophages and dendritic cells: Trends in Microbiology

J Virol. 1995 Feb; 69(2): 1059C1070.

Virus-induced immunosuppression: immune system-mediated destruction of virus-infected dendritic cells results in generalized immune suppression.
P Borrow, C F Evans, and M B Oldstone
Department of Neuropharmacology, Scripps Research Institute, La Jolla, California 92037.

Despite the clinical importance of virus-induced immunosuppression, how virus infection may lead to a generalized suppression of the host immune response is poorly understood. To elucidate the principles involved, we analyzed the mechanism by which a lymphocytic choriomeningitis virus (LCMV) variant produces a generalized immune suppression in its natural host, the mouse. Whereas adult mice inoculated intravenously with LCMV Armstrong rapidly clear the infection and remain immunocompetent, inoculation with the Armstrong-derived LCMV variant clone 13, which differs from its parent virus at only two amino acid positions, by contrast results in persistent infection and a generalized deficit in responsiveness to subsequent immune challenge. Here we show that the immune suppression induced by LCMV clone 13 is associated with a CD8-dependent loss of interdigitating dendritic cells from periarteriolar lymphoid sheaths in the spleen and, functionally, with a deficit in the ability of splenocytes from infected mice to stimulate the proliferation of naive T cells in a primary mixed lymphocyte reaction. Dendritic cells are not depleted in immunocompetent Armstrong-infected mice. LCMV Armstrong and clone 13 exhibit differences in their tropism within the spleen, with clone 13 causing a higher level of infection of antigen-presenting cells in the white pulp, including periarterial interdigitating dendritic cells, than Armstrong, thereby rendering these cells targets for destruction by the antiviral CD8+ cytotoxic T-lymphocyte response which is induced at early times following infection with either virus. Our findings illustrate the key role that virus tropism may play in determining pathogenicity and, further, document a mechanism for virus-induced immunosuppression which may contribute to the clinically important immune suppression associated with many virus infections, including human immunodeficiency virus type

Virus-induced immunosuppression: immune system-mediated destruction of virus-infected dendritic cells results in generalized immune suppression.

Int J Mol Sci. 2018 Sep; 19(9): 2821.
Published online 2018 Sep 18. doi: 10.3390/ijms19092821
Monocytes and Macrophages as Viral Targets and Reservoirs

Ekaterina Nikitina,1,2,3,* Irina Larionova,3,4 Evgeniy Choinzonov,5 and Julia Kzhyshkowska3,6
Author information Article notes Copyright and License information Disclaimer
1Department of Episomal-Persistent DNA in Cancer- and Chronic Diseases, German Cancer Research Center, 69120 Heidelberg, Germany
2Department of Oncovirology, Cancer Research Institute, Tomsk National Research Medical Center, Russian Academy of Sciences, Tomsk 634050, Russia
3Department of Translational Cellular and Molecular Biomedicine, Tomsk State University, Tomsk 634050, Russia; ur.liam@_fortim (I.L.); ed.grebledieh-inu.amdem@akswokhsyhzk.ailuJ (J.K.)
4Department of Molecular Oncology and Immunology, Cancer Research Institute, Tomsk National Research Medical Center, Russian Academy of Sciences, Tomsk 634050, Russia
5Head and Neck Department, Cancer Research Institute, Tomsk National Research Medical Center, Russian Academy of Sciences, Tomsk 634050, Russia; ur.cmint@vonoznyohc
6Institute of Transfusion Medicine and Immunology, Medical Faculty Mannheim, Heidelberg University, 68167 Heidelberg, Germany

Viruses manipulate cell biology to utilize monocytes/macrophages as vessels for dissemination, long-term persistence within tissues and virus replication.

Viruses enter cells through endocytosis, phagocytosis, macropinocytosis or membrane fusion. These processes play important roles in the mechanisms contributing to the pathogenesis of these agents and in establishing viral genome persistence and latency.

Upon viral infection, monocytes respond with an elevated expression of proinflammatory signalling molecules and antiviral responses, as is shown in the case of the influenza, Chikungunya, human herpes and Zika viruses. Human immunodeficiency virus initiates acute inflammation on site during the early stages of infection but there is a shift of M1 to M2 at the later stages of infection. Cytomegalovirus creates a balance between pro- and anti-inflammatory processes by inducing a specific phenotype within the M1/M2 continuum.

Despite facilitating inflammation, infected macrophages generally display abolished apoptosis and restricted cytopathic effect, which sustains the virus production.

The majority of viruses discussed in this review employ monocytes/macrophages as a repository but certain viruses use these cells for productive replication. This review focuses on viral adaptations to enter monocytes/macrophages, immune escape, reprogramming of infected cells and the response of the host cells.

Keywords: monocyte/macrophage, virus, persistence, reservoir, cell response, inflammation, cancer

Monocytes and Macrophages as Viral Targets and Reservoirs