Impairment of cellular but not humoral immune responses in chronic pulmonary and disseminated paracoccidioidomycosis in mice

Abstract

Humoral and cellular immune responses were measured during the progression of chronic pulmonary and disseminated paracoccidioidomycosis in mice. The chronic disease was established by pulmonary infection of mice with different doses of the yeast form of Paraccidioides brasiliensis isolate GAP. Levels of antibodies to P. brasiliensis, detected in serum by immunodiffusion and enzyme-linked immunosorbent assay, directly correlated with the size of the infectious challenge. Significant delayed-type hypersensitivity (DTH) responses to antigen were largely restricted to week 1 after pulmonary infection with intranasally administered high doses (5.0 x 106 or 1.1 x 107 CFU per inoculum). In vitro lymphoproliferative of peripheral blood lymphocytes (PBL) to P. brasiliensis antigens were significant only at 2 weeks after infection with intranasally administered 1.1 x 107 CFU. Responses of PBL to concanavalin A were depressed (50% of control response) as early as 8 weeks and reached a nadir at 10 to 18 weeks after infection. Infected mice made antibodies to sheep erythrocytes (SRBC) (109 intravenously [i.v.]) normally at all times tested after infection. In contrast, infected mice sensitized to SRBC) (106 i.v.) had significantly depressed DTH responses to SRBC at 9 and 20 weeks postinfection compared with noninfected mice. These results indicated that in this model, normal humoral responses developed to homologous and heterologous antigens. In contrast, the T cellular immune responses were depressed with progression and chronicity of the disease. Thus, this model closely mimics the immunological findings in human paracoccodioidomycosis.