INDUCTION OF IN-VITRO HUMAN MACROPHAGE ANTI-MYCOBACTERIUM TUBERCULOSIS ACTIVITY - REQUIREMENT FOR IFN-GAMMA AND PRIMED LYMPHOCYTES

Mycobacterium tuberculosis (Mtb) is the world's leading infectious cau se of mortality. Despite the overwhelming data supporting the critical role of cellular immunity, little is known of the early microbial and immune cell interactions and whether human macrophages can be activat ed to express anti-Mtb activity, We report the reconstitution of an in vitro system whereby human macrophages express anti-Mtb activity only in coculture with PBL and with IFN-gamma. Omission of IFN-gamma in th e cocultures or il Mtb lysate/IFN-gamma-primed lymphocytes was associa ted with high growth of Mtb, high IL-10 and IL-12 p40, nearly undetect able IL-12 p70 levels, and the highest percentages of CD4 and CD8 T ce lls. In contrast, IFN-gamma treatment of cocultures containing Mtb lys ate/IFN-gamma-primed PBL reduced bacilli count by similar to 2.5 log, decreased the production of IL-10 by 5.7-fold, increased IL-12 p70 by similar to 50-fold, and reduced the percentages of CD4 and CD8 T cells , Activation of anti-Mtb activity was time and dose dependent, At 2000 U/ml of IFN-gamma, bactericidal activity was achieved (10-fold reduct ion from initial inoculum), Anti-Mtb activity against several strains of M. tuberculosis (H37Ra and H37Rv, and C, a clinical isolate) was ob served and was associated with expression of inducible nitric oxide sy nthase, These data suggest that induction of human macrophage anti-Mtb activity required dual signaling from PBL and IFN-gamma, Thus, the de velopment of an in vitro human system may greatly facilitate studies t o delineate immune cells, cytokines, and effector functions/genes crit ical in controlling Mtb, Defining the mechanisms may also provide nove l treatment strategies for tuberculosis.