Macrophage expression of class II major histocompatibility complex gene products in Paracoccidioides brasiliensis-infected mice

C57B1/6 isogenic mice infected with Paracoccidioides brasiliensis strains s howed a disruption in the expression of la antigen. Expression slowly decre ased during the course of the infection with a slight variation dependent o n the route of inoculation and the fungal strain used, but production of in terferon-gamma and tumor necrosis factor-alpha were observed. Suppression o f Ia antigen expression and depression of the immunoproliferative responses of spleen cells were strongly correlated with nitric oxide levels. These p arameters were inhibited when the animals were treated with nitro-L-arginin e, which resulted in inhibition the activation of nitric oxide (NO) product ion. Analysis of the data showed that changes in the expression of the Ia a ntigen occur in P. brasiliensis infection and are strongly correlated with NO levels. These phenomena may be interrelated and reflect macrophage activ ation that contributes to the control of the disease and to the immunosuppr ession observed during the course of the infection.