BCG-INDUCED GRANULOMA-FORMATION IN MURINE TISSUES

BCG infection of mice provides a convenient model to study natural and cellular immunity to mycobacteria and the mechanisms of granuloma formation and repair. We have used a range of macrophage (M Phi membrane molecules and secretory products to investigate resident M Phi-pathogen interactions and T lymphocyte-dependent recruitment and activation of M Phi in different tissues of immature, normal adult and gamma interferon deficient animals. In situ hybridization (ISH), RT-PCR and immunocytochemical analysis of M Phi, gene and product expression have been correlated with in vitro study of endocytic and secretory activity in which biogel polyacrylamide bead-elicited peritoneal M Phi, are exposed to Th1 and Th2 cytokines, LPS, BCG and other stimuli. The role of resident and newly recruited M Phi responding to BCG in liver, spleen, lung and brain has been defined by means of antigen markers expressed by M Phi (F4/80, 7/4, CR3, macrosialin, sialoadhesin and scavenger receptor) and/or T and B lymphoid cells (MHC Class II, CD4, CD8, B220). Heterogeneity in M Phi, secretory activity was revealed by ISH analysis of lysozyme, TNF-alpha, IL-1 IL-6 and MCP-1, by in vitro assay of NO and superoxide anion production, and by RT-PCR studies of Th1 (interferon gamma) and Th2 (IL-4, IL-I3, IL-10) lymphokine mRNA in tissues. Our studies confirm the importance of interferon gamma as a critical mediator of host resistance to mycobacterial infection and raise intriguing questions in regard to T cell and M Phi functional heterogeneity in distinct tissue microenvironments.