RESUMEN
Natural resistance and acquired immune responses to Paracoccidioides brasiliensis infection were investigated employing resistant and susceptible inbred mice infected with Pb18, a virulent isolate. Intraperitoneally infected susceptible mice present an innefficient macrophage activation, depressed DTH reactions, high levels of specific antibodies mainly of the IgG2b and IgA isotypes, evident polyclonal activation of IgG1, IgG2b and IgG2a producing B cells and a progressive disease. Resistant mice on the contrary, present an efficient macrophage activation, adequate DTH responses, low levels of specific antibodies mainly of the IgG2a isotype and absence of polyclonal activation of B cell resulting in the resolution of the infectious process. Similar results were obtained when the intratracheal or intravenous routes of infection were used. The previous subcutaneous infection with Pb18 establishes a stable cell-mediated immunity that makes the innately susceptible B10. A mice resistant to P. brasiliensis ip infection. This murine model, which mimics the benign and severe chronic forms of the human disease, is proposed as a framework of our current knowledge of the host-parasite interactions in paracoccidioidomycosis and as a basis ofor future challenge in continuing analyses.