Mycopathologia 126: 137-146, 1994. © 1994 KluwerAcademic Publishers. Printedin the Netherlands. Delayed-type hypersensitivity response in an isogenic murine model of paracoccidioidomycosis Raquel dos Anjos Fazioli, ~'2 Lticia Mary Singer-Vermes, 1 Suely Sanae Kashino, 1 Eva Burger, 1 Marcello Fabiano De Franco, 3 Maura Moscardi-Bacchi 3 & Vera Lticia Garcia Calich ~ t Departamento de Imunologia, Instituto de Ci6ncias Biomddicas, Universidade de S6o Paulo, S~o Paulo, Brasil; 2Sefdo de Imunologia, Instituto Adolfo Lutz, Sgo Paulo, Brasil; 3Departamento de Patologia, Faculdade de Medicina de Botucatu, UNESP, Botucatu, S~o Paulo, Brasil Received 13 October 1993; accepted in revisedform 25 January 1994 Abstract. The specific delayed-type hypersensitivity (DTH) response was evaluated in resistant (A/SN) and susceptible (B10.A) mice intraperitoneally infected with yeasts from a virulent (Pbl8) or from a non-virulent (Pb265) Paracoccidioides brasiliensis isolates. Both strains of mice were footpad challenged with homologous antigens. Pb18 infected A/SN mice developed an evident and persistent DTH response late in the course of the disease (90th day on) whereas B10.A animals mounted a discrete and ephemeral DTH response at the 14th day post-infection. A/SN mice infected with Pb265 developed cellular immune responses whereas B10.A mice were almost always anergic. Histological analysis of the footpads of infected mice at 48 hours after challenge showed a mixed infiltrate consisting of predominantly mononu- clear cells. Previous infection of resistant and susceptible mice with Pb18 did not alter their DTH responses against heterologous unrelated antigens (sheep red blood cells and dinitrofluorobenzene) indicating that the observed cellular anergy was antigen-specific. When fungal related antigens (candidin and histoplasmin) were tested in resistant mice, absence of cross-reactivity was noted. Thus, specific DTH responses against P. brasiliensis depend on both the host's genetically determined resistance and the virulence of the fungal isolate. Key words: Cellular immune response, Delayed-type hypersensitivity, Isogenic murine model, P. brasili- ensis Abbreviations: DTH, delayed-type hypersensitivity; DNFB, dinitrofluorobenzene; FN18, Fava Netto's antigen obtained from isolate Pb18; FN265, Fava Netto's antigen obtained from isolate Pb265; SRBC, sheep red blood cells Introduction Paracoccidioidomycosis (PCM) is a chronic gran- ulomatous disease caused by the dimorphic fungus Paracoccidioides brasiliensis [1]. As in other deep mycosis, cell-mediated immunity (CMI) has been ascribed as the most important host defense mechanism against this fungus [2- 4]. Usually progressive or disseminated forms of the disease are associated with depressed cellular immune responses and high levels of specific anti- bodies [5-7]. Our previous studies established an isogenic murine model of PCM. It was shown that A/SN and B10.A mice are respectively very resistant and susceptible animals to intraperitoneal (i.p.) infection with a virulent P. brasiliensis isolate (Pb18) [8] and that resistance was linked to a