Helper T cell interactions.

Studies of the relationship between carrier-primed helper T cell dose and the antibody response to a hapten on that carrier reveal evidence for two synergistic T helper cells. One of these two T cells is absent in agammaglobulinemic mice. This finding is not due to suppression; instead, T helper cells from these mice interact synergistically with T helper cells from normal mice, as would be predicted if two populations of cells are present in normal mice, while only one is present in the agammaglobulinemic mice. These findings, taken together with studies in similar systems, suggest that one of the two T helper cells recognizes immunoglobulin on B cells, while the other is specific for carrier. It remains to be determined whether both cells show the phenomenon of major histocompatibility complex restriction, or whether this a property of one of the cells only. It is also not clear whether the Ig-recognizing T cell is also carrier specific, or whether its apparent carrier specificity in this system reflects an ability of the carrier to bring together Ig and an I region gene product into a unique configuration on the B cell surface.