Experimental paracoccidioidomycosis in the Syrian hamster. Morphology and correlation of lesions with humoral and cell-mediated immunity.

Male hamsters (105) received intratesticular injection of suspension of a live yeast phase culture of Paracoccidioides brasiliensis and were sacrificed weekly during 20 weeks. Humoral immunity was studied by the agar-gel immunodiffusion (ID) and indirect immunofluorescence (IF) tests. Cell-mediated immunity was determined by the macrophage migration inhibition test in the presence of phytohemagglutinin (PHA) and Paracoccidioides brasiliensis soluble antigen (PbAg). The morphology of the lesions was studied in the inoculation site, lymph nodes, lung, liver, spleen and kidneys. Disseminated paracoccidioidomycosis was observed in 100% of the animals after the first week. The lesions were initially made up of fungi surrounded by polymorphonuclear neutrophils and macrophages. Up to the 10th week the majority of the lesions appeared as compact confluent ephitelioid granulomas containing rare large fungi, some showing sings of degeneration. At this time, the specific antibody titers and the cellular immune response to PHA and PbAg were highest. From the 11th week on the granulomas became less compact, edematous with the epithelioid cells loosely arranged. This change was accompanied by an increase in the number of fungi showing reproductive activity and was associated with renal amyloidosis and progressive decline of cellular immune response both to PHA and PbAg. Contrariwise the titers of circulating antibodies were maintained. In the present model, disseminated paracoccidioidomycosis of the hamster was associated with depression of cellular immunity, change in the pattern of the granuloma, intense fungi proliferation and amyloidosis.