We show that the IgD-induced augmentation of the immune response to trinitrophenylated keyhole limpet hemocyanin can be transferred to syngeneic mice with spleen cells from IgD-injected donors. The augmenting activity is present in the Lyt-1+2-, L3T4+ T cell population and is absent from B cells. The ability of transferred T cells to augment the immune response correlates with the presence of a high frequency of Lyt-1+2- T cells that form rosettes with IgD-coated sheep erythrocytes (T delta cells). Such rosette-forming cells can also be induced by incubation of spleen cells from normal donors in IgD-coated petri dishes. Injection of normal spleen cells exposed to IgD-coated petri dishes together with antigen also augments the immune response of recipients. The existence of a regulatory circuit based upon interactions between T delta cells, antigen, B cell surface IgD, and serum IgD, is proposed.

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