Selected populations of alloreactive T cells contain helper T cells but lack ThId, an antigen-specific helper T cell required for dominant production of the T15 idiotype.

Isolated, alloreactive T cell populations were primed with protein carriers in vivo and tested for their ability to provide help for an anti-phosphorylcholine (PC) antibody response and for production of the T15 idiotype. It was found that alloreactive T cell populations would support anti-PC antibody response but did not selectively activate B cells capable of producing the T15 idiotype that normally dominates such responses. This failure to help for the production of the T15 idiotype was shown to be due to the absence of an antigen-specific helper T cell that is required for dominant idiotype production (ThId). These studies suggest that ThId cells have recognition structures for antigen and for self idiotype, but lack recognition structures for major histocompatibility complex-encoded antigens.