scholarly journals IFN-γ-independent control of M. tuberculosis requires CD4 T cell-derived GM-CSF and activation of HIF-1α

2021 ◽  
Author(s):  
Erik Van Dis ◽  
Huntly M Morrison ◽  
Daniel M Fines ◽  
Janet Peace Babirye ◽  
Lily H McCann ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Tuberculosis Infection ◽  
Cd4 T Cell ◽  
Independent Control ◽  
Functional Link ◽  
Gm Csf ◽  
Ifn Γ

The prevailing model of protective immunity to tuberculosis is that CD4 T cells produce the cytokine IFN-γ to activate bactericidal mechanisms in infected macrophages. Recent evidence has expanded this model, and it is now clear that CD4 T cells can control M. tuberculosis infection in the absence of IFN-γ production. To identify factors and pathways involved in IFN-γ-independent control, we developed a co-culture model using CD4 T cells isolated from the lungs of infected mice and M. tuberculosis-infected murine bone marrow-derived macrophages (BMDMs). We show that IFN-γ-independent control is primarily mediated by CD4 T cell production of the cytokine GM-CSF and requires activation of the macrophage transcription factor HIF-1α. HIF-1α activation drives a metabolic shift toward aerobic glycolysis and leads to the production of lipid droplets, both of which support host defense against infection. Surprisingly, recombinant GM-CSF is insufficient to rescue the absence of control by GM-CSF-deficient CD4 T cells during co-culture with BMDMs. In peritoneal macrophages, GM-CSF is sufficient to control growth, induces lipid droplet biogenesis, and requires HIF-1α expression for control. While HIF-1α-mediated control following IFN-γ stimulation requires nitric oxide, we find that HIF-1α activation by CD4 T cells and recombinant GM-CSF is nitric oxide-independent, implying a distinct pathway of activation. In addition to GM-CSF, CD4 T cells produce a factor that helps maintain phagosome membrane integrity during infection and blocks bacterial access to host lipids, a primary nutrient source. These results advance our understanding of CD4 T cell-mediated immunity to M. tuberculosis, clarify the role of nitric oxide as primarily immunomodulatory during M. tuberculosis infection, and reveal a novel mechanism for the activation of HIF-1α. Furthermore, we establish a previously unknown functional link between GM-CSF and HIF-1α and provide evidence that CD4 T cell-derived GM-CSF is a potent bactericidal effector.

scholarly journals Depletion of Cd4+ T Cells Causes Reactivation of Murine Persistent Tuberculosis despite Continued Expression of Interferon γ and Nitric Oxide Synthase 2

2000 ◽  
Vol 192 (3) ◽  
pp. 347-358 ◽  
Author(s):  
Charles A. Scanga ◽  
V.P. Mohan ◽  
Keming Yu ◽  
Heather Joseph ◽  
Kathryn Tanaka ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
T Cells ◽  
T Cell ◽  
Persistent Infection ◽  
Cd4 T Cells ◽  
Macrophage Activation ◽  
Latent Tuberculosis ◽  
Cd4 T Cell ◽  
Ifn Γ ◽  
Oxide Synthase

Tuberculosis is a major cause of death in much of the world. Current estimates are that one-third of the world's population is infected with Mycobacterium tuberculosis. Most infected persons control the infection but in many cases may not eliminate the organism. Reactivation of this clinically latent infection is responsible for a large proportion of active tuberculosis cases. A major risk factor for reactivation of latent tuberculosis is HIV infection, suggesting a role for the CD4+ T cell subset in maintaining the latent persistent infection. In this study, we tested the requirement for CD4+ T cells in preventing reactivation in a murine model of latent tuberculosis. Antibody-mediated depletion of CD4+ T cells resulted in rapid reactivation of a persistent infection, with dramatically increased bacterial numbers in the organs, increased pathology in the lungs, and decreased survival. Although CD4+ T cells are believed to be a major source of interferon (IFN)-γ, expression of the gene for IFN-γ in the lungs of CD4+ T cell–depleted mice was similar to that in control mice. In addition, inducible nitric oxide synthase production and activity was unimpaired after CD4+ T cell depletion, indicating that macrophage activation was present even during CD4+ T cell deficiency. These data indicate that CD4+ T cells are necessary to prevent reactivation but may have roles in addition to IFN-γ production and macrophage activation in controlling a persistent tuberculous infection.

scholarly journals HIV-1 Viremia Prevents the Establishment of Interleukin 2–producing HIV-specific Memory CD4+ T Cells Endowed with Proliferative Capacity

2003 ◽  
Vol 198 (12) ◽  
pp. 1909-1922 ◽  
Author(s):  
Souheil-Antoine Younes ◽  
Bader Yassine-Diab ◽  
Alain R. Dumont ◽  
Mohamed-Rachid Boulassel ◽  
Zvi Grossman ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Cd4 T Cell ◽  
Memory Cells ◽  
Cell Responses ◽  
Specific Memory ◽  
Ifn Γ ◽  
Memory Cd4 T Cells

CD4+ T cell responses are associated with disease control in chronic viral infections. We analyzed human immunodeficiency virus (HIV)-specific responses in ten aviremic and eight viremic patients treated during primary HIV-1 infection and for up to 6 yr thereafter. Using a highly sensitive 5-(and-6)-carboxyfluorescein diacetate-succinimidyl ester–based proliferation assay, we observed that proliferative Gag and Nef peptide-specific CD4+ T cell responses were 30-fold higher in the aviremic patients. Two subsets of HIV-specific memory CD4+ T cells were identified in aviremic patients, CD45RA− CCR7+ central memory cells (Tcm) producing exclusively interleukin (IL)-2, and CD45RA− CCR7− effector memory cells (Tem) that produced both IL-2 and interferon (IFN)-γ. In contrast, in viremic, therapy-failing patients, we found significant frequencies of Tem that unexpectedly produced exclusively IFN-γ. Longitudinal analysis of HIV epitope–specific CD4+ T cells revealed that only cells that had the capacity to produce IL-2 persisted as long-term memory cells. In viremic patients the presence of IFN-γ–producing cells was restricted to periods of elevated viremia. These findings suggest that long-term CD4+ T cell memory depends on IL-2–producing CD4+ T cells and that IFN-γ only–producing cells are short lived. Our data favor a model whereby competent HIV-specific Tcm continuously arise in small numbers but under persistent antigenemia are rapidly induced to differentiate into IFN-γ only–producing cells that lack self-renewal capacity.

scholarly journals CD4 T-Cell-Mediated Demyelination Is Increased in the Absence of Gamma Interferon in Mice Infected with Mouse Hepatitis Virus

2002 ◽  
Vol 76 (14) ◽  
pp. 7329-7333 ◽  
Author(s):  
Lecia Pewe ◽  
Jodie Haring ◽  
Stanley Perlman
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Hepatitis Virus ◽  
Mouse Hepatitis Virus ◽  
Gamma Interferon ◽  
Cd4 T Cell ◽  
Immune Mediated ◽  
Donor Cells ◽  
Ifn Γ

ABSTRACT Mice infected with the murine coronavirus, mouse hepatitis virus, strain JHM (MHV) develop an immune-mediated demyelinating encephalomyelitis. Adoptive transfer of MHV-immune splenocytes depleted of either CD4 or CD8 T cells to infected mice deficient in recombination activation gene 1 resulted in demyelination. We showed previously that the process of CD8 T-cell-mediated demyelination was strongly dependent on the expression of gamma interferon (IFN-γ) by donor cells. In this report, we show, in contrast, that demyelination and lymphocyte infiltration were increased in recipients of IFN-γ−/− CD4 T cells when compared to levels in mice receiving C57BL/6 CD4 T cells.

scholarly journals Enteral Immunization with Attenuated Recombinant Listeria monocytogenes as a Live Vaccine Vector: Organ-Dependent Dynamics of CD4 T Lymphocytes Reactive to a Leishmania major Tracer Epitope

2003 ◽  
Vol 71 (3) ◽  
pp. 1083-1090 ◽  
Author(s):  
Hélène Saklani-Jusforgues ◽  
Elisabeth Fontan ◽  
Neirouz Soussi ◽  
Geneviève Milon ◽  
Pierre L. Goossens
Keyword(s):  
T Cells ◽  
Listeria Monocytogenes ◽  
T Cell ◽  
Cd4 T Cells ◽  
Leishmania Major ◽  
Cd4 T Cell ◽  
Interleukin 4 ◽  
Cell Immune Response ◽  
Mesenteric Lymph Nodes ◽  
Ifn Γ

ABSTRACT Listeria monocytogenes is considered as a potential live bacterial vector, particularly for the induction of CD8 T cells. The CD4 T-cell immune response triggered after enteral immunization of mice has not yet been thoroughly characterized. The dynamics of gamma interferon (IFN-γ)- and interleukin-4 (IL-4)-secreting CD4 T cells were analyzed after priming through intragastric delivery of an attenuated ΔactA recombinant L. monocytogenes strain expressing the Leishmania major LACK protein; a peptide of this protein, LACK158-173 peptide (pLACK), is a well-characterized CD4 T-cell target in BALB/c mice. Five compartments were monitored: Peyer's patches, mesenteric lymph nodes (MLN), spleen, liver, and blood. A single intragastric inoculation of ΔactA-LACK-LM in BALB/c mice led to colonization of the MLN and spleen at a significant level for at least 3 days. Efficient priming of IFN-γ-secreting pLACK-reactive CD4 T cells was observed in all tested compartments. Interestingly, IL-4-secreting pLACK-reactive CD4 T cells were detectable at day 6 or 7 only in blood and liver. The absence of translocation of viable bacteria through the intestinal epithelium after further ΔactA-LACK-LM inoculations was concomitant with the absence of an increase in the level of IFN-γ secreted by the MLN, blood, and splenic pLACK-reactive Th1 T cells, although the levels remained significantly above the basal level. No change in this population size was detected in the spleen. However, an increase in the number of intragastric inoculations had a clinical beneficial effect in L. major-infected BALB/c mice. L. monocytogenes thus presents the potential of an efficient vector for induction of CD4 T cells when administered by the enteral route.

scholarly journals Organ- and Disease-Stage-Specific Regulation of Toxoplasma gondii-Specific CD8-T-Cell Responses by CD4 T Cells

2006 ◽  
Vol 74 (10) ◽  
pp. 5790-5801 ◽  
Author(s):  
Sonja Lütjen ◽  
Sabine Soltek ◽  
Simona Virna ◽  
Martina Deckert ◽  
Dirk Schlüter
Keyword(s):  
T Cells ◽  
T Cell ◽  
Toxoplasma Gondii ◽  
Cd8 T Cells ◽  
Functional Activity ◽  
Cd4 T Cells ◽  
Cd8 T Cell ◽  
Cd4 T Cell ◽  
Ifn Γ

ABSTRACT Toxoplasma gondii induces a persistent central nervous system infection, which may be lethally reactivated in AIDS patients with low CD4 T-cell numbers. To analyze the role of CD4 T cells for the regulation of parasite-specific CD8 T cells, mice were infected with transgenic T. gondii expressing the CD8 T-cell antigen β-galactosidase (β-Gal). Depletion of CD4 T cells prior to infection did not affect frequencies of β-Gal876-884-specific (consisting of residues 876 to 884 of β-Gal) CD8 T cells but resulted in a pronounced reduction of intracerebral β-Gal-specific gamma interferon (IFN-γ)-producing and cytolytic CD8 T cells. After cessation of anti-CD4 treatment a normal T. gondii-specific CD4 T-cell response developed, but IFN-γ production of intracerebral β-Gal-specific CD8 T cells remained impaired. The important supportive role of CD4 T cells for the optimal functional activity of intracerebral CD8 T cells was also observed in mice that had been depleted of CD4 T cells during chronic toxoplasmosis. Reinfection of chronically infected mice that had been depleted of CD4 T cells during either the acute or chronic stage of infection resulted in an enhanced proliferation of β-Gal-specific IFN-γ-producing splenic CD8 T cells. However, reinfection of chronically infected mice that had been depleted of CD4 T cells in the acute stage of infection did not reverse the impaired IFN-γ production of intracerebral CD8 T cells. Collectively, these findings illustrate that CD4 T cells are not required for the induction and maintenance of parasite-specific CD8 T cells but, depending on the stage of infection, the infected organ and parasite challenge infection regulate the functional activity of intracerebral CD8 T cells.

scholarly journals The Role of β-Catenin in Th1 Immune Response against Tuberculosis and Profiles of Expression in Patients with Pulmonary Tuberculosis

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Kunlong Xiong ◽  
Jinxia Niu ◽  
Ruijuan Zheng ◽  
Zhonghua Liu ◽  
Yanzheng Song ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Cd4 T Cells ◽  
Mononuclear Cells ◽  
Cd4 T Cell ◽  
Cell Frequency ◽  
Tnf Α ◽  
Ifn Γ

β-Catenin is a key molecule of canonical Wnt/β-catenin pathway. Its roles and expression profiles in T cells of tuberculosis (TB) remain unclear. The aim of this study was to explore the role of β-catenin in CD4+ T cells and its expression characteristics in patients with pulmonary tuberculosis (PTB). In this study, CD4+ T cell-specific β-catenin conditional knockout mice (β-CAT-cKO mice) were aerosol infected with Mycobacteria tuberculosis (Mtb) H37RV with wild-type mice as controls. Four weeks after infection, the mRNA expression of IFN-γ, TNF-α, and TCF-7 in the lungs of mice was measured. CD4, CD8, β-catenin, IFN-γ, and TNF-α in mononuclear cells from the lungs and spleens were measured by flow cytometry, and the pathological changes of lungs were also observed. Patients with PTB were enrolled, with blood samples collected and PBMCs isolated. The expressions of β-catenin, IFN-γ, TNF-α, and PD-1 in CD4+ and CD8+ T cells were measured by flow cytometry. Results showed a decreased frequency of and reduced IFN-γ/TNF-α mRNA expression and secretion by CD4+ T cells in the lungs of infected β-CAT-cKO mice compared with infected wild-type controls, and only slightly more inflammatory changes were observed in the lungs. β-catenin expressions in CD4+ and CD8+ T cells were significantly decreased in blood cells of patients with severe PTB compared with those in mild PTB. The stimulation of peripheral blood mononuclear cells (PBMCs) with lithium chloride (LiCl), a stimulant of β-catenin, resulted in the increase in CD4+ T cell frequency, as well as their secretion of IFN-γ and TNF-α. β-Catenin demonstrated a moderately positive correlation with PD-1 in CD4+ T cells. β-Catenin along with PD-1 and IFN-γ in CD4+ T cells had a high correlation with those in CD8+ T cells. In conclusion, β-catenin may be involved in the regulation of Th1 response and CD4+ T cell frequency in TB.

Wilms Tumor Protein-1-Derived 9-Mer Peptide Induces CD4 T-Cell Responses in an HLA-DR Restricted Manner

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 4351-4351
Author(s):  
Shigeo Fuji ◽  
Julia Fischer ◽  
Markus Kapp ◽  
Thomas G Bumm ◽  
Hermann Einsele ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
T Cell Responses ◽  
Class Ii ◽  
Hla Class Ii ◽  
Cd4 T Cell ◽  
Cell Responses ◽  
Hla Dr ◽  
Ifn Γ

Abstract Abstract 4351 Wilms‘ tumor protein-1 (WT1) is one of the most investigated tumor-associated antigens (TAA) in hematological malignancies. CD8 T-cell responses against several WT1-derived peptides have been characterized and are known to contribute to disease control after allogeneic hematopoietic stem cell transplantation (HSCT). Also the identification of human leukocyte antigen (HLA) class II-restricted CD4 T-cell epitopes from WT1 is a challenging task of T-cell-based cancer immunotherapy to improve the effectiveness of WT1 peptide vaccination. We found a highly immunogenic WT1 peptide composed of only 9 amino acids having the ability to induce IFN-γ secretion in CD4 T-cells in an HLA DR-restricted manner. This finding is of great interest as it was generally accepted that HLA class II binding peptides are composed of at least 12 amino acids being recognized by CD4 T-cells, whereas HLA class I binding peptides are composed of 8–11 amino acids being recognized by CD8 T-cells (Wang et al Mol. Immunol. 2002). However, both HLA class I and class II molecules bind to primary and secondary peptide anchor motifs covering the central 9–10 amino acids. Thus, considering this common structural basis for peptide binding there is a possibility that the WT1 9-mer peptide binds to HLA class II molecules, and induces CD4 T-cell responses. IFN-γ induction in response to several WT1 9-mer peptides was screened in 24 HLA-A*02:01 positive patients with acute myeloid leukemia or myelodysplastic syndrome after allogeneic HSCT. Responses to one WT1 9-mer peptide were exclusively detected in CD3+CD4+ T-cells of 2 patients after allogeneic HSCT, but not in CD3+CD4+ T-cells of their corresponding HSC donors. CD4+ T-cell responses to this WT1 9-mer peptide exhibited high levels of functional avidity, as IFN-γ induction was detected after stimulation with 100 ng peptide per mL. Peptide-induced IFN-γ production was confirmed with IFN-γ ELISPOT assays and the HLA restriction of the T-cell response was determined by HLA blocking antibodies. The reaction was significantly blocked by anti-pan HLA class II antibody (85 % reduction), but neither by pan-HLA class I nor by anti-HLA A2 antibody. To identify the subtype of HLA class II molecule, blocking assays with antibodies against HLA-DP, HLA-DR and HLA-DQ were performed. IFN-γ induction was completely abrogated by anti-HLA-DR antibody (99 % reduction) (fig 1, p value of unpaired student‘s t-test <0.0001 for the medium control vs anti-pan HLA class II antibody or anti-HLA-DR antibody, respectively). To test whether IFN-γ was exclusively induced in CD4 T cells, CD4 or CD8 T-cells were depleted from PBMC. Whereas CD8 T-cell depletion did not affect IFN-γ induction, CD4 T-cell depletion completely abrogated the WT1 9-mer peptide induced response (fig 2). CD4 T-cells responding to the WT1 9-mer peptide were indicated to be functional cytotoxic T-cells with an effector CD4 T-cell phenotype. Longitudinal analyses demonstrated the persistence and functionality of WT1 9-mer specific CD4 T-cells in PBMC of patients even at day 1368 after allogeneic HSCT. These data indicate for the first time that a TAA-derived 9-mer peptide can induce HLA class II-restricted CD4 T-cell responses. Vaccination with the characterized WT1 9-mer peptide can enhance the induction and maintenance of not only CD4 but also indirect CD8 T-cell responses. Considering that CD4 T-cells play an important role in tumor rejection, the possibility that other TAA-derived 9-mer peptides having the potential to induce CD4 T-cell responses should be explored in other settings of tumor immunology as well to improve vaccination strategies. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Immune profiling of Mycobacterium tuberculosis-specific T cells in recent and remote infection

2020 ◽  
Author(s):  
Cheleka A.M. Mpande ◽  
Virginie Rozot ◽  
Boitumelo Mosito ◽  
Munyaradzi Musvosvi ◽  
One B Dintwe ◽  
...  
Keyword(s):  
T Cells ◽  
Mycobacterium Tuberculosis ◽  
T Cell ◽  
T Cell Activation ◽  
Cd4 T Cells ◽  
Cell Activation ◽  
Differentially Expressed ◽  
Cd4 T Cell ◽  
Remote Infection ◽  
Ifn Γ

AbstractBackgroundRecent Mycobacterium tuberculosis (M.tb) infection is associated with a higher risk of progression to tuberculosis disease, compared to persistent infection after remote exposure. However, current immunodiagnostic tools fail to distinguish between recent and remote infection. We aimed to characterise the immunobiology associated with acquisition of M.tb infection and identify a biomarker that can distinguish recent from remote infection.MethodsHealthy South African adolescents were serially tested with QuantiFERON-TB Gold to define recent (QuantiFERON-TB conversion <6 months) and persistent (QuantiFERON-TB+ for >1.5 year) infection. We characterized M.tb-specific CD4 T cell functional (IFN-γ, TNF, IL-2, CD107, CD154), memory (CD45RA, CCR7, CD27, KLRG-1) and activation (HLA-DR) profiles by flow cytometry after CFP-10/ESAT-6 peptide pool or M.tb lysate stimulation. We then assessed the diagnostic performance of immune profiles that were differentially expressed between individuals with recent or persistent QuantiFERON-TB+.FindingsCFP-10/ESAT-6-specific CD4 T cell activation but not functional or memory phenotypes distinguished between individuals with recent and persistent QuantiFERON-TB+. In response to M.tb lysate, recent QuantiFERON-TB+ individuals had lower proportions of highly differentiated IFN-γ+TNF+ CD4 T cells expressing a KLRG-1+ effector phenotype and higher proportions of early differentiated IFN-γ-TNF+IL-2+ and activated CD4 T cells compared to persistent QuantiFERON-TB+ individuals. Among all differentially expressed T cell features CFP-10/ESAT-6-specific CD4 T cell activation was the best performing diagnostic biomarker of recent infection.InterpretationRecent M.tb infection is associated with highly activated and moderately differentiated functional M.tb-specific T cell subsets, that can be used as biomarkers to distinguish between recent and remote infection.

scholarly journals Differential Role of Gamma Interferon in Inhibiting Pulmonary Eosinophilia and Exacerbating Systemic Disease in Fusion Protein-Immunized Mice Undergoing Challenge Infection with Respiratory Syncytial Virus

2007 ◽  
Vol 82 (5) ◽  
pp. 2196-2207 ◽  
Author(s):  
Elaine M. Castilow ◽  
Matthew R. Olson ◽  
David K. Meyerholz ◽  
Steven M. Varga
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Systemic Disease ◽  
Cd4 T Cell ◽  
Pulmonary Eosinophilia ◽  
F Protein ◽  
Rsv Infection ◽  
Ifn Γ ◽  
Syncytial Virus

ABSTRACT Secondary exposure to respiratory syncytial virus (RSV) can lead to immunopathology and enhanced disease in vaccinated individuals. Vaccination with individual RSV proteins influences the type of secondary RSV-specific immune response that develops upon challenge RSV infection, as well as the extent of immunopathology. RSV-specific memory CD4 T cells can directly contribute to immunopathology through their cytokine production. Immunization of BALB/c mice with a recombinant vaccinia virus (vv) expressing the attachment (G) protein of RSV results in pulmonary eosinophilia upon RSV challenge, whereas immunization of mice with a vv expressing the fusion (F) protein does not. We analyzed the CD4 T-cell response to an I-Ed-restricted CD4 T-cell epitope within the F protein of RSV corresponding to amino acids 51 to 66 in an effort to better understand the similarities and differences in the immune response elicited by the G versus the F protein. Vaccination with the G protein induces a mixture of RSV G-specific Th1 and Th2 cells with a restricted T-cell receptor repertoire. In contrast, we demonstrate here that immunization with the F protein elicits a broad repertoire of RSV F-specific CD4 T cells that predominantly exhibit a Th1 phenotype. However, in the absence of gamma interferon (IFN-γ), RSV F51-66-specific CD4 T cells secreted interleukin-5, and mice developed pulmonary eosinophilia after RSV challenge. IFN-γ-deficient mice exhibited decreased weight loss compared to wild-type controls, suggesting that IFN-γ exacerbates systemic disease. These data demonstrate that IFN-γ can have both beneficial and detrimental effects during a secondary RSV infection.

scholarly journals Interferon γ Eliminates Responding Cd4 T Cells during Mycobacterial Infection by Inducing Apoptosis of Activated Cd4 T Cells

2000 ◽  
Vol 192 (1) ◽  
pp. 117-122 ◽  
Author(s):  
Dyana K. Dalton ◽  
Laura Haynes ◽  
Cong-Qiu Chu ◽  
Susan L. Swain ◽  
Susan Wittmer
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Population ◽  
Cd4 T Cells ◽  
Interferon Γ ◽  
Cd4 T Cell ◽  
Wild Type ◽  
Normal Numbers ◽  
Large Expansion ◽  
Ifn Γ

In Mycobacterium bovis Bacille Calmette-Guérin (BCG)-infected wild-type mice, there was a large expansion of an activated (CD44hi) splenic CD4 T cell population followed by a rapid contraction of this population to normal numbers. Contraction of the activated CD4 T cell population in wild-type mice was associated with increased apoptosis of activated CD4 T cells. In BCG-infected interferon (IFN)-γ knockout (KO) mice, the activated CD4 T cell population did not undergo apoptosis. These mice accumulated large numbers of CD4+CD44hi T cells that were responsive to mycobacterial antigens. Addition of IFN-γ to cultured splenocytes from BCG-infected IFN-γ KO mice induced apoptosis of activated CD4 T cells. IFN-γ–mediated apoptosis was abolished by depleting adherent cells or Mac-1+ spleen cells or by inhibiting nitric oxide synthase. Thus, IFN-γ is essential to a regulatory mechanism that eliminates activated CD4 T cells and maintains CD4 T cell homeostasis during an immune response.

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