FIG. 1.

Magnitude and isotype profiles of serum antibody responses to i.m. immunization with inactivated PR8 virus in CD4⁺ T-cell-deficient and immunocompetent mice. CD4⁺ T-cell-deficient mice or C57BL/6 mice (16 weeks old) were immunized i.m. with 10 μg of inactivated PR8 virus per mouse. The mice were boosted with the same dose after 15 days. Con, unimmunized CD4⁺ T-cell-deficient mice (n = 5). CD4KO, CD4⁺ T-cell-deficient mice received inactivated PR8 virus (n = 5). C57B/6: C57BL/6 immunocompetent mice received inactivated PR8 virus (n = 5). Prime, samples were measured 15 days after first immunization. Boost, samples were measured 10 days after boost. Serum samples were assayed in 1:400 and 1:1,600 dilutions. Error bars in this and subsequent figures represent standard error.