Lack of correlation between delayed-type hypersensitivity and host resistance to Plasmodium chabaudi infection.

C57B1/6J mice immunized with Plasmodium chabaudi antigen plus saponin exhibited strong delayed-type hypersensitivity (DTH) reactions to footpad injections of P. chabaudi antigen. However, when immunized mice were challenged with P. chabaudi parasites, DTH was significantly depressed after 3 days of infection. This DTH depression coincided with a steep rise in the titre of malarial antibody in these immunized challenged mice when compared to unchallenged immunized mice. Serum from mice recovering from P. chabaudi infection depressed DTH levels of immunized mice significantly, but spleen cells from convalescent mice only slightly reduced the DTH levels. These results are discussed with respect to the role of cell-mediated immunity in malaria infections.