The systemic but not mucosal Th2 response to H. polygyrus is impaired in CD28KO mice

CD28KO mice exhibit a pronounced mucosal immune response after oral inoculation of the infectious parasite, H. polygyrus (HP), which is associated with elevations in: T cell cytokine production; spleen and mesenteric lymph node (MLN) germinal center (GC) formation; and serum IgG1 and IgE levels, comparable to that observed in HP-inoculated CD28+/+ controls. In this study we examined the systemic immune response to HP to examine whether parenteral administration of this antigen also elicits a T-dependent CD28-independent immune response. BALB/c CD28KO and control mice were intraperitoneally injected with HP larvae. Serum IgG1 and IgE, but not IgG2a, elevations were detected by day 13 after parenteral immunization, but were not as elevated as observed in HP-parenterally immunized CD28+/+ mice. Spleen GC formation was markedly increased at day 14 after HP-parenteral immunization of BALB/c CD28+/+ mice; however, and in striking contrast, increases in GC formation were blocked in HP-parenterally immunized CD28KO mice. These studies suggest differences in CD28 requirements following mucosal versus parenteral immunization during the Th2 in vivo immune response. In the absence of CD28, mucosal immunization leads to a pronounced T and B cell response while the response following systemic immunization with the same antigen is severely impaired.