Selective expansion of human gamma delta T cells by monocytes infected with live Mycobacterium tuberculosis.

Gamma delta (gamma delta) T cell receptor (TCR) expressing T cells comprise 3% of human peripheral blood lymphocytes, yet their role in the immune response remains largely unknown. There is evidence both in humans and in animal models that these cells participate in the immune response to mycobacterial antigens. In mice, exposure to mycobacterial antigens leads to the expansion of gamma delta T cells in draining lymph nodes and lungs. In humans, gamma delta T cell lines with reactivity to mycobacterial antigens have been derived from synovial fluid of a rheumatoid arthritis patient, skin lesions of leprosy patients, and peripheral blood of a healthy tuberculin reactor. Very little is known, however, about the factors which induce human gamma delta T cells to expand. In studies comparing the human T cell response to live and heat-killed Mycobacterium tuberculosis (MT), we have found that monocytes infected with live MT are very effective inducers of human gamma delta T cell expansion. After 7 d of exposure to live MT, gamma delta T cells were greatly increased in all healthy tuberculin reactors (PPD+) tested and frequently were the predominant T cell population. In contrast, heat-killed MT or purified protein products of MT induced a CD4+, alpha beta TCR+ T cell response with very little increase in gamma delta T cells. Furthermore, a similar selective induction of gamma delta T cells was observed when monocytes infected with live Salmonella were used to stimulate T cells. Heat-killed Salmonella, like heat-killed MT, induced a predominantly CD4+ alpha beta TCR+ T cell response. These findings suggest that human gamma delta T cells are a major reactive T cell population during the early stages of infection with living intracellular bacteria and are therefore likely to exert an important role in the initial interaction between host and parasite.

Human Mycobacterium tuberculosis-reactive CD4+ T-cell clones: heterogeneity in antigen recognition, cytokine production, and cytotoxicity for mononuclear phagocytes.

CD4+ T cells regulate the protective immune response which follows exposure to Mycobacterium tuberculosis by activating macrophages through the cytokines the CD4+ T cells secrete. In addition CD4+ T cells have been shown to be directly cytotoxic for antigen-pulsed mononuclear phagocytes (monocytes-macrophages). To explore the functional interaction between mycobacterial antigen-specific CD4+ T cells and mononuclear phagocytes further, CD4+ T-cell clones were derived from healthy purified protein derivative-positive individuals. Five T-cell clones were selected for detailed analysis. None responded to the purified recombinant or native mycobacterial antigens of 14, 19, 65, 71, and 30 (alpha-antigen/Ag6) kDa. However, the T-cell clones demonstrated heterogeneity in antigen recognition as measured by their Western blot (immunoblot) responses. Some T-cell clones made only interleukin 2, while others made only interleukin 4; all produced gamma interferon, although in differing amounts. Four of five T-cells clones were cytotoxic for purified protein derivative-pulsed monocytes at 1:1 and 10:1 effector-target cell ratios. When monocytes infected with live M. tuberculosis were used as targets, comparable levels of cytotoxicity were observed. The cytotoxicity was major histocompatibility complex class II restricted and inhibited by antibodies to ICAM-1 and LFA-1 and not by antibodies to tumor necrosis factor alpha, lymphotoxin, and gamma interferon. Cytotoxicity by CD4+ T cells for monocytes pulsed with mycobacterial antigens or infected with live M. tuberculosis is a common property of these cells and appears to be independent of the repertoire of lymphokines produced and not limited to recognition of defined mycobacterial heat shock proteins. Lysis of heavily infected mononuclear phagocytes may be one manner in which CD4+ T cells regulate host immune response to M. tuberculosis.

Bacterial antigen activation of Vdelta1 and Vdelta2 gammadelta T cells of persons infected with human immunodeficiency virus type 1.

Vdelta2 gammadelta T cells are readily activated by microbial antigens. In persons infected with human immunodeficiency virus type 1 (HIV-1), the number of gammadelta T cells remains the same or increases in association with reversal of the Vdelta2/Vdelta1 ratio from > or = 1 to < 1. Vdelta2 T cell responses to microbial antigens were tested in 11 HIV-1-infected (> or = 500 CD4 cells/mm3) and 7 uninfected persons. In persons with HIV-1 infection, Mycobacterium tuberculosis expanded Vdelta2 cells in 1 person as did Salmonella typhimurium in 4; however, Candida albicans antigens did not lead to more Vdelta2 cells. Vdelta2 responses to M. tuberculosis were enhanced by interleukin (IL)-2 in HIV-1-infected persons (from 1 subject to 7; P < .01) and were associated with increased interferon-gamma production. Bacterial antigens and IL-2 increased HIV-1 replication; M. tuberculosis antigens induced the greatest increase. Thus, in HIV-1-infected persons with > or = 500 CD4 cells/mm3, Vdelta2 T cell responses to bacterial antigens remain intact.

Role of the mononuclear phagocyte as an antigen-presenting cell for human gamma delta T cells activated by live Mycobacterium tuberculosis.

gamma delta T cells, both human and murine, have been found to be highly responsive to mycobacterial antigens. However, the role and function of gamma delta T cells in the immune response to Mycobacterium tuberculosis remain largely unknown. In earlier studies, we demonstrated that monocytes infected with live M. tuberculosis were particularly effective inducers of human peripheral blood gamma delta T cells. The present studies were performed to further characterize the interaction between human mononuclear phagocytes, gamma delta T cells, and live M. tuberculosis, in comparison with CD4+ T cells. First, we found that resting gamma delta T cells expanded in vitro by live M. tuberculosis were specific for M. tuberculosis, and that heat killing and washing the mycobacteria removed the antigen(s) for gamma delta T cells. In contrast, the heat-killed mycobacteria retained significant antigenicity for CD4+ T cells. Second, live M. tuberculosis-expanded gamma delta T cells from healthy tuberculin-positive donors did not respond significantly to the antigens in M. tuberculosis culture filtrate, including the 65- and 71-kDa mycobacterial heat shock proteins. Third, the activation of gamma delta T cells by live mycobacteria was dependent on antigen-presenting cells, and mononuclear phagocytes were found to be very efficient antigen-presenting cells both for resting peripheral blood gamma delta T cells and for activated expanded gamma delta T cells. The mononuclear phagocyte carried the necessary costimulatory factors necessary for gamma delta T-cell proliferation. Fourth, the antigen repertoire and HLA requirements for CD4+ memory T cells and those for gamma delta T cells appear to be quite distinct from each other. CD4+ T cells recognized both soluble protein antigens and whole organisms in a class II major histocompatibility complex-restricted manner, whereas gamma delta T cells appeared to recognize only constituents associated with the whole organism and were not restricted by class I or class II major histocompatibility complex molecules. Finally, the assay system described to expand and purify responding CD4+ and gamma delta T cells after stimulation with live M. tuberculosis represented a simple approach to the direct comparison of these two T-cell populations in the interaction with mononuclear phagocytes infected with M. tuberculosis. Such studies provide insight not only into the relative roles of human CD4+ and gamma delta T cells in the human immune response to intracellular bacterial pathogens such as M. tuberculosis but also into the basic biologic role of human gamma delta T cells in antimicrobial immunity.

Characterization of a 10- to 14-kilodalton protease-sensitive Mycobacterium tuberculosis H37Ra antigen that stimulates human gamma delta T cells.

gamma delta T-cell receptor-bearing T cells (gamma delta T cells) are readily activated by intracellular bacterial pathogens such as Mycobacterium tuberculosis. The bacterial antigens responsible for gamma delta T-cell activation remain poorly characterized. We have found that heat treatment of live M. tuberculosis bacilli released into the supernatant an antigen which stimulated human gamma delta T cells. gamma delta T-cell activation was measured by determining the increase in percentage of gamma delta T cells by flow cytometry in peripheral blood mononuclear cells stimulated with antigen and by proliferation of gamma delta T-cell lines with monocytes as antigen-presenting cells. Supernatant from heat-treated M. tuberculosis was fractionated by fast-performance liquid chromatography (FPLC) on a Superose 12 column. Maximal gamma delta T-cell activation was measured for a fraction of 10 to 14 kDa. Separation of the supernatant by preparative isoelectric focusing demonstrated peak activity at a pI of < 4.0. On two-dimensional gel electrophoresis, the 10- to 14-kDa FPLC fraction contained at least seven distinct molecules, of which two had a pI of < 4.5. Protease treatment reduced the bioactivity of the 10- to 14-kDa FPLC fraction for both resting and activated gamma delta T cells. Murine antibodies raised to the 10- to 14-kDa fraction reacted by enzyme-linked immunosorbent assay with antigens of 10 to 14 kDa in lysate of M. tuberculosis. In addition, gamma delta T cells proliferated in response to an antigen of 10 to 14 kDa present in M. tuberculosis lysate. gamma delta T-cell-stimulating antigen was not found in culture filtrate of M. tuberculosis but was associated with the bacterial pellet and lysate of M. tuberculosis. These results provide a preliminary characterization of a 10- to 14-kDa, cell-associated, heat-stable, low-pI protein antigen of M. tuberculosis which is a major stimulus for human gamma delta T cells.

Activation of human CD8+ alpha beta TCR+ cells by Mycobacterium tuberculosis via an alternate class I MHC antigen-processing pathway.

Human immune responses to M. tuberculosis are characterized by activation of multiple T cell subsets including CD4+, CD8+, and gammadelta T cells, and the role of CD8+ alphabeta TCR+ T cells in this response is poorly understood. Stimulation of T cells from healthy tuberculin skin test-positive persons with live M. tuberculosis-H37Ra or soluble M. tuberculosis Ags readily up-regulated IL-2Ralpha (CD25) expression on CD8+ T cells. Purified resting and activated CD8+ T cells produced IFN-gamma and proliferated to both M. tuberculosis bacilli and soluble mycobacterial Ags with monocytes as APC. Precursor frequency of mycobacterial Ag-specific CD8+ T cells by IFN-gamma enzyme-linked immunospot was 5-10-fold lower than the precursor frequency of CD4+ T cells, and IFN-gamma secretion by CD8+ T cells was 50-100-fold lower. CD8+ T cells secreted approximately 10-fold less IFN-gamma per cell than CD4+ T cells in response to mycobacterial Ags. CD8+ T cell responses to M. tuberculosis bacilli were blocked by anti-MHC class I antibody and required Ag processing. Processing of M. tuberculosis bacilli by monocytes for presentation to MHC class I-restricted CD8+ T cells was insensitive to brefeldin A treatment, which blocks the conventional MHC class I Ag-processing pathway. These results represent the first demonstration that human cells can process pathogen Ags via an alternate Ag-processing pathway for MHC class I and suggest a mechanism for participation of IFN-gamma-secreting CD8+ T cells in the human immune responses to M. tuberculosis.

Serum interleukin-6 (IL-6), IL-10, tumor necrosis factor (TNF) alpha, soluble type II TNF receptor, and transforming growth factor beta levels in human immunodeficiency virus type 1-infected individuals with Mycobacterium avium complex disease.

To characterize changes in serum cytokine levels in human immunodeficiency virus type 1 (HIV-1)-infected persons with Mycobacterium avium complex (MAC) bacteremia, the levels of IL-1alpha (interleukin-1alpha), IL-6, IL-10, tumor necrosis factor alpha (TNF-alpha), soluble type II TNF receptor (sTNF-RII), and transforming growth factor beta (TGF-beta) in serum were measured in two cohorts of HIV-1-infected persons with MAC bacteremia. The first cohort was part of a MAC prophylaxis study. Patients with bacteremia were matched with controls without bacteremia. Elevated IL-6, IL-10, TNF-alpha, sTNF-RII, and TGF-beta levels were noted at baseline for all subjects, a result consistent with advanced HIV-1 disease. IL-1alpha was not detected. No differences in cytokine levels in serum were noted at baseline and at the time of bacteremia between patients with MAC and controls. In the second cohort, subjects had serum samples collected at the time of MAC bacteremia and thereafter while on macrolide therapy. Serum samples at time of bacteremia were collected from HIV-1-infected persons at a time when neither highly active antiretroviral therapy (HAART) nor MAC prophylaxis was used routinely. MAC treatment resulted in decreased levels of IL-6 and TNF-alpha in serum, which were evident for IL-6 by 4 to 6 weeks and for TNF-alpha by 8 to 16 weeks. Thus, antibiotic treatment for MAC results in decreased levels of IL-6 and TNF-alpha in serum in HIV-1-infected persons who are not on HAART.