Responses of athymic (“nude”) mice to sheep red blood cells

Abstract “Nude” (thymusless) mice immunized with sheep red cells gave rise to indirect PFC in numbers (per million spleen cells) that were comparable to those of normal animals for days 2 ‐ 4, but declined sharply thereafter. Hemolysin and hemagglutinin titers follow essentially the pattern of the direct PFC response. About two‐thirds of nude animals also formed some indirect hemolytic plaques which are interpreted as due to 7 S (IgG) globulins rather than to low efficiency 19 S (IgM) globulins. In the secondary response, nude mice failed to exceed their primary performance in any of the four parameters measured: direct PFC, indirect PFC, hemolysin titers and hemagglutinin titers, thus demonstrating the thymus dependence of immunological memory. The initial spurt of immunological reactions by nude animals, followed by premature decline suggest a failure of proliferation or recruitment of immunologically responding cell population in the absence of a thymus.