Mechanism of enhanced antigen presentation by B cells activated with anti-μ plus interferon-γ: Role of B7-2 in the activation of naive and memory CD4+ T cells

B cells activated with anti-γ antibody plus interferon (IFN)-γ exerted strong antigen presentation activity for T cell proliferation. The enhanced antigen presentation function was shown to be due to the increase in B7-2 expression. When B cells were stimulated with anti-μ, expression of MHC major histocompatibility complex class II, heat-stable antigen (HSA), ICAM-1 and B7-2 was increased. The presence of IFN-γ further augmented the expression of B7-2 on anti-μ-stimulated B cells. B7-1 was not expressed on B cells under these conditions. The participation of B7-2 in the elicitation of the proliferative response of T cells was confirmed by the inclusion of anti-B7-2 antibody in cultures. The enhanced expression of either HSA or ICAM-1 was shown not to play a major role in the increased B cell antigen presentation capacity. The major T cell population responding to this activated B cell antigen presentation was shown to be CD44^low naive CD4⁺ T cells, whereas CD45RB^low memory CD4⁺ T cells responded only weakly. The difference in proliferative responses between naive and memory CD4⁺ T cells was explained by the different efficiency in IL-2 production of these cell populations in response to antigen presentation by B cells activated by anti-μ plus IFN-γ. These results suggest that IFN-γ plays an important role in recruitment of naive T cells for an immune response.