Interferon-gamma-mediated effects upon immunity to coccidial infections in the mouse

The effect of treatment with a monoclonal antibody (MoAb) capable of neutralising interferon-gamma (IFN-gamma) on the course of coccidial infections in mice (C57BL/6 and NIH infected with Eimeria vermiformis or E. pragensis, and BALB/c infected with E. pragensis) was examined. The results differed with the species of parasite, the strain of mouse, the measure of infection and whether the infection was a primary or secondary one. The replication of E. vermiformis in primary infections was enhanced in both C57BL/6 and NIH mice, but less MoAb was required in NIH than in C57BL/6 to produce similar effects. In neither strain did treatment prevent priming or interfere with the complete immunity to challenge normally induced by moderate infection with E. vermiformis. The replication of E. pragensis in primary infections was not affected in any of the strains of mouse but the clinical effects were exacerbated. Priming with E. pragensis was unaffected by treatment but the partial immunity to challenge, normally induced by infection with this species, was reduced when MoAb was given 2 h before challenge. This reduction was evident as an increased faecal output of oocysts and loss of body weight. These results confirm the role of IFN-gamma in resistance to coccidiosis and further emphasise the complexity of the immune response in this disease.