Memory T cells enhance the expression of high-avidity naive B cells

The secondary immune response classically differs from the primary response in magnitude, avidity, and isotype of the antibodies produced. Cell transfer studies to assess the contribution of memory B and memory T cells to each of these parameters are described. Avidities of the anti-DNP plaque-forming cells (PFC) generated in lethally irradiated recipients of naive B cells and keyhole limpet hemocyanine (KLH)-primed T cells, followed by immunization with soluble DNPKLH, are medium to high, and do not differ significantly from the avidities of anti-DNP PFC in recipients of DNP-primed B cells and KLH-primed T cells. However, the number of indirect (I)-PFC and the ratio of I-PFC to direct (D)-PFC are significantly greater in the recipients of primed B and primed T cells. The results suggest that carrier primed T cells can selectively activate virgin B cells which are committed to produce medium- and high-avidity antibodies, and/or enhance the generation of somatic mutation which leads to antibodies of higher avidity. Priming of B cells is necessary for the increased magnitude of the I-PFC.