Immune response to Trichinella spiralis in the rat. I. Development of cellular and humoral responses during chronic infection.

The immune response of rats to infection with Trichinella spiralis was studied serially for more than 1 year. Initial antigen-specific cellular reactivity, assessed by the lymphocyte transformation response, developed in the draining mesenteric nodes 3 days after infection. After 1 week reactive lymphocytes were detectable in the spleen and circulating blood, but the more 'remote' peripheral nodes did not harbor antigen-reactive cells until late in the second week. Thereafter, the patterns of antigen-responsiveness varied among the different lymphoid pools, but in all cases a decline in reactivity was seen after the first month. Serum hemagglutinating and homocytotropic antibodies, detectable by the tenth day, reached their peaks after 1 month of infection. Hemagglutinating titers persisted for more than 1 year but homocytotropic antibody was lost over this period. Comparisons are drawn between the evolution of the natural infection and the development of the host's immune response.