Effect of Trichinella spiralis infection on delayed hypersensitivity to heterologous antigens.

Studies were initiated to determine the effects of the different phases of the nematode life cycle on the delayed-type hypersensitivity (DTH) capabilities of the host. Mice were injected intraperitoneally with 4 X 10(6) viable or heat-killed BCG at 0, 3, 7, 14 and 28 days after oral infection with 200 Trichinella spiralis larvae. Groups were tested for DTH 28 days after BCG inoculation by the footpad swelling assay. Infection with T. spiralis was found to suppress the response in mice administered viable BCG 0 or 3 days later. Mice injected with viable bacteria 7 days after T. spiralis regained the ability to develop in vivo DTH reactions against old tuberculin. Groups administered viable BCG 14 and 28 days after nematode infection yielded potentiated DTH responses, when compared with control mice. Animals infected with T. spiralis and later injected with heat-killed BCG required a longer interval to develop specific immunopotentiation. Maximum immunopotentiation seemed to be related to the presence of larvae in muscle tissue (28 days). These findings suggest that the effect of T. spiralis on the immune capabilities of the host is dependent on the different anatomical locations of the parasite.