Class II MHC function in macrophages and mice infected with Mycobacterium

by 1972- Nepal, Rajeev Mani

The interaction between macrophages and CD4+ T cells is central to the adaptive immune response against Mycobacterium tuberculosis (MTB). The primary goal of this thesis was to determine if macrophages infected with pathogenic Mycobacterium spp can function in the processing and presentation of antigens via the class II MHC pathway. To this end, we first characterized the endocytic proteases available to the infected macrophage. We found that the maturation of Cat L into its' two-chain active forms is impaired in macrophages harboring either M. avium or M. tuberculosis, rendering these cells deficient in the predominant intracellular, and extracellular active forms of the enzyme. Secondly, we showed that DM, but not Cat B, -S, or -L, is absolutely required to control a primary aeorosl infection of mice with MTB. MTB specific CD4+ T cells were not elicited in the absence of DM. The data suggest that most, if not all MTB antigens require DM for presentation by class II molecules to CD4+ T cells. Thirdly, we demonstrated that macrophages of distinct lineages and activation states differ in the ability to process and present mycobacteria derived antigens via class II MHC molecules. The data showed that GM-CSF derived bone marrow macrophages were significantly more efficient than M-CSF derived bone marrow macrophages at processing M. avium and M. tuberulosis bacilli (live or dead) for presentation of the immunodominant anigen, Ag85B, to specific T cells. The varying ability of each cell type to function in antigen presentation when infected may contribute to the ability of mycobacteria to persist in the host. Finally, we showed that the phagocytosis of M. avium by macrophages result in the ii generation of more stable nascent class II-peptide complexes at the cell surface, that are capable of stimulating antigen specific CD4+ T cells for prolonged periods. iii