Mycobacterium tuberculosis 19-kilodalton lipoprotein inhibits Mycobacterium smegmatis-induced cytokine production by human macrophages in vitro

Vaccination of mice with Mycobacterium vaccae or M. smegmatis induces some protection against M, tuberculosis challenge, The 19-kDa lipoprotein of M. tuberculosis, expressed in M. vaccae or M, smegmatis (M. smeg19kDa), abroga tes this protective immunity. To investigate the mechanism of this suppress ion of immunity, human monocyte-derived macrophages (MDM) were infected wit h M. smeg19kDa. Infection resulted in reduced production of tumor necrosis factor alpha (TNF-alpha) (P < 0.01), interleukin-12 (IL-12) (P < 0.05), IL- 6 (P < 0.05), and IL-10 (P < 0.05), compared to infection with M. smegmatis vector (M. smegV), Infection with M, smeg19kDa and with M. smegV had no di fferential effect on expression of costimulatory molecules on MDM, nor did it affect the proliferation of presensitized T cells cocultured with infect ed MDM. When MDM were infected with M. smegmatis expressing mutated forms o f the 19-kDa lipoprotein, including non-O-glycosylated (M, smeg19NOG), nons ecreted (M.smeg19NS), and nonacylated (M. smeg19NA) variants, the reduced p roduction of TNF-alpha or IL-12 was not observed. When the purified 19-kDa lipoprotein aas added directly to cultures of infected monocytes, there was little effect on either induction of cytokine production or its inhibition . Thus, the immunosuppressive effect is dependent on glycosylated and acyla ted 19-kDa lipoprotein present in the phagosome containing the mycobacteriu m. These results suggest that the diminished protection against challenge w ith M. tuberculosis seen in mice vaccinated with M. smegmatis expressing th e 19-kDa lipoprotein is the result of reduced TNF-alpha and IL-12 productio n, possibly leading to reduced induction of T-celi activation.