Interferon-gamma (IFN-gamma)-dependent protection and synthesis of chemoattractants for mononuclear leucocytes caused by IL-12 in the lungs of mice infected with Cryptococcus neoformans

We have recently demonstrated that IL-12 induced cellular inflammatory resp onses consisting mainly of accumulation of mononuclear leucocytes in the lu ngs of mice infected with Cryptococcus neoformans and protected mice agains t fulminant infection. We examined the involvement of endogenously synthesi zed IFN-gamma in such a response by investigating the effects of a neutrali zing monoclonal antibody against this cytokine. The latter treatment comple tely abrogated the positive effects of IL-12 on survival of infected mice a nd prevented IL-12-induced elimination of microbials from the lungs. Histop athological examination showed that accumulation of mononuclear leucocytes in the infected lungs caused by IL-12 was clearly inhibited by anti-IFN-gam ma MoAb. We also examined the local production of mononuclear cell-attracti ng chemokines such as monocyte chemotactic protein-1 (MCP-1), regulated upo n activation, normal T cell expressed and secreted (RANTES), macrophage inf lammatory protein-1 alpha (MIP-1 alpha), MIP-1 beta and IFN-gamma-inducible protein 10 (IP-10) in the lungs using a reverse transcriptase-polymerase c hain reaction (RT-PCR) method. We found that these chemokines were not synt hesized in the infected lungs, while IL-12 treatment markedly induced their production. Interestingly, neutralizing anti-IFN-gamma MoAb strongly suppr essed IL-12-induced production of these chemokines. Similar results were ob tained with MCP-1 and MIP-1 alpha when their synthesis was measured at the protein level using respective ELISA kits. Our results indicate that IFN-ga mma plays a central role in the protective effects of IL-12 by inducing mon onuclear leucocyte-attracting chemokines and cellular inflammatory response s.