Expression of T cell receptor V beta 8 determinants on antigen-specific T helper factor.

The ability of cell-free T helper cell products to provide helper activity in B cell antibody responses has been studied. The supernatants of activated T helper cells were sufficient to support hapten-specific IgG antibody responses by B cells in the absence of intact T cells. Moreover, this help was both antigen-specific and major histocompatibility complex (MHC)-restricted: T cell clone supernatant helped only when the hapten recognized by B cells was covalently linked to the carrier protein for which the corresponding T helper cell was specific; and this help was effective in supporting responses of only those B cells which express an MHC type corresponding to the MHC specificity of the cloned T cell. Active T helper supernatants consisted of at least two components, both of which are necessary for B cell responses. One is the lymphokine interleukin 4 (IL-4). The other is an antigen- and MHC-specific product which has been affinity purified by binding to a monoclonal antibody specific for T cell alpha beta receptor V beta 8 determinants. It therefore appears that a shed or secreted factor with serologic and functional similarities to the alpha beta T cell receptor (TCR) has been isolated and shown to be capable of direct signaling of B lymphocytes.