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Infection and Immunity


Geisel School of Medicine


Cell-mediated immunity has been reported to play an important role in defense against Encephalitozoon cuniculi infection. Previous studies from our laboratory have underlined the importance of cytotoxic CD8+ T lymphocytes (CTL) in survival of mice infected with E. cuniculi. In the present study, immune response against E. cuniculi infection in CD4+T-cell-deficient mice was evaluated. Similar to resistant wild-type animals, CD4−/− mice were able to resolve E. cuniculi infection even at a very high challenge dose (5 × 107 spores/mouse). Tissues from infected CD4−/−mice did not exhibit higher parasite loads in comparison to the parental wild-type mice. Conversely, at day 21 postinfection, susceptible CD8−/− mice had 1014times more parasites in the liver compared to control wild-type mice. Induction of the CD8+ T-cell response in CD4−/− mice against E. cuniculi infection was studied. Interestingly, a normal antigen-specific CD8+T-cell response to E. cuniculi infection was observed in CD4−/− mice (precursor proliferation frequency, 1/2.5 × 104 versus 1/104 in wild-type controls). Lack of CD4+ T cells did not alter the magnitude of the antigen-specific CTL response (precursor CTL frequency; 1/1.4 × 104 in CD4−/− mice versus 1/3 × 104 in control mice). Adoptive transfer of immune CD8+ T cells from both CD4−/− and wild-type animals prevented the mortality in CD8−/− mice.E. cuniculi infection thus offers an example of an intracellular parasitic infection where CD8+ T-cell immunity can be induced in the absence of CD4+ T cells.