Kinetics of murine delayed-type hypersensitivity response to Eimeria falciformis (Apicomplexa: Eimeriidae).

Mice recovering from a primary infection with an intestinal protozoan parasite, Eimeria falciformis (Apicomplexa: Eimeriidae), showed a classic delayed-type hypersensitivity (DTH) reaction to oocyst antigen challenge. This reaction was characterized by a biphasic pattern of footpad swelling. The first swelling peaked at 2 h after antigen challenge, whereas the second swelling peaked at 24 to 48 h after challenge. The DTH reaction was transferable with a T-cell-enriched spleen cell population from mice that had recovered from E. falciformis infection. Cytotoxic depletion of immune T cells with anti-L3T4 antibody and complement abrogated DTH transfer, indicating that L3T4-positive T cells were required. A T-cell-enriched spleen cell population from acutely infected mice suppressed the transfer of DTH with immune cells from recovered animals, implicating the existence of infection-induced immunoregulatory cells controlling the parasite-specific immune response during infection. Immune spleen cells also transferred resistance to infection as measured by oocyst production and death rate of recipients. Together, these results indicate that the DTH reaction, induced by infection with E. falciformis, is mediated by L3T4-positive T cells and is associated with resistance to infection.