In summary, while published studies indicate that B cells may have important role in the cooperative immune response against tumours, our use of MHC-restriction to isolate the in vivo effects of tumour-specific B cells on tumour-specific CD4+ T cells indicate that primary cognate interactions between CD4+ T cells and B cells are unlikely to serve as a major mechanism of CD4+ T cell activation. The gene discussed is CD4; the disease is neoplasm.