The vertebrate immune system includes numerous interacting proteins involved in the recognition and elimination of parasitic organisms. The general goal of this research is to understand the evolution of key molecular components of this system, particularly the molecules encoded by the major histocompatibility complex (MHC), and to understand how immunogenic proteins of parasitic organisms have evolved under natural selection exerted by the host's immune system. The MHC is a multi-gene gamily encoding cell-surface glycoproteins which play an important role in the immune system, binding foreign peptides and presenting them to T cells, thereby triggering an appropriate immune response. Certain MHC loci are highly polymorphic in humans and other vertebrates, and recent analyses of DNA sequence data have provided evidence that this polymorphism is maintained by positive selection favoring the ability to bind and present a variety of foreign peptides. Therefore the MHC provides an excellent system for studying the evolution of immune recognition and the role of infectious disease as an agent of natural selection. The methods will involve statistical analysis of published DNA sequences, of which there are a large number now available for MHC genes of several mammalian species; for other immune system genes; and for genes of parasites encoding immunogenic proteins. The purpose of these analyses will be as follows: (10 to test the hypothesis that polymorphism at MHC loci is maintained by overdominant selection relating to disease resistance and to understand the role of recombination in generating new MHC alleles; (2) to test the hypothesis that the vertebrate immune system has exerted selection on proteins of parasitic organisms to evade recognition by the host; and (30 to understand the evolutionary history and patterns of co-evolution of MHC genes and other genes playing important roles in the immune system (including T cell receptors, integrins, Fc receptors, the C3/C4/C5 complement component family, and the ABC family of transmembrane transporters). GRANTS=R01HL51630 Alveolar Macrophages (AM) are the first line of cellular defense against inhaled infectious agents such as MTB. Yet almost nothing is known about the capacity of AM from healthy or TB patients to ingest and inhibit the growth of MTB. Our preliminary data indicate that the effector function of AM for avirulent MTB exceeds that of blood monocytes (MN), in part because of increased release of tumor necrosis factor-alpha (TNF) which serves as a macrophage activating factor (MAF). By contrast, AM are weak producers of transforming growth factor beta (TGFbeta), a deactivating cytokine. Mononuclear phagocytes in tuberculous granulomas, however, express TGFbeta, as do MN from TB patients. AM from healthy subjects are primed for effector function against MTB, but TB may be associated with release of deactivating cytokines such as TGFbeta. AM from healthy subjects nonspecifically suppress T lymphocyte responses to antigenic and mitogenic and mitogenic stimuli. During TB, MN specifically suppress T cell responses to tuberculin purified protein derivative (PPD) possibly through increased TGFbeta which is immunosuppressive. Also during TB, peripheral blood mononuclear cells (PBMC) are nonresponsive to the secreted 30 Kd antigen (alphaag) of MTB; as the alphaag is a direct stimulus for cytokine production by MN, this unresponsiveness may be due to cytokine-induced suppression by MN. These considerations lead us to the hypothesis that in TB, AM are specifically suppressive of T cell responses to PPD (and the alphaag) and deactivated for killing of the organism through increased expression of cytokines such as TGFbeta. Together, and separately, immunosuppression and decreased effector function contribute to the pathogenesis of TB in the lung. TB afflicts HIV-infected persons early in their course while tuberculin skin tests are still positive and CD4 counts relatively intact suggesting that disturbances in effector function against MTB may be operant. We hypothesize that these AM are defective in killing of MTB due to increased expression of deactivating cytokines which override MAFs. Th1- type cytokines are protective in certain animal models. We hypothesize that in TB granulomas, macrophages express deactivating cytokines such as TGFbeta and T cells fail to optimally express a Thi-type pattern of cytokines. In TB granulomas from HIV=-infected persons, the cellular architecture is distorted with a further decrease in Th1-type cytokines produced by T cells; concurrent production of deactivating cytokines by mononuclear phagocytes leads to an inexorable increase in load of AFB within granulomas.
The Specific Aims to test these hypotheses are: 1. To examine the immunosuppressive activity and mediators of suppression of AM from patients with pulmonary TB for blood T cell responses to tuberculin PPD and the alphaag; and to compare alveolar and blood lymphocyte responsiveness to these stimuli including production of Th1 and Th2 cytokines, and their respective cytotoxicity for antigen-pulsed and MTB-infected AM. 2. To assess the intracellular growth of virulent MTB in AM from patients with TB; their production of and response to macrophage activating and deactivating cytokines; and the modulatory effects of HIV infection. 3. To characterize the cellular architecture and the pattern of cytokine expression in pulmonary granulomas from patients with TB with or without HIV using the complementary approaches of immunofluorescence. RNA PCR, in situ hybridization, and immunohistochemistry.
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