One must first emphasize that helper T cells can only respond to antigen presented by macrophage MHC class II antigens as a complex on APC cells. In turn, they recognize the same combination of antigen and class II MHC antigens on the corresponding B cells. It is only then that the helper T cell secretes its cytokines to activate the reaction. T cells recognize antigen in the context of their own MHC configuration. They will not cooperate with B cells and macrophages expressing antigens of a different genetic bacground.