Guinea pigs immunized with 2,4-dinitrophenyl-guinea pig albumin (DNP-GPA) possess lymphocytes which specifically bind sufficient DNP-GPA-125I to their surface to be detected by radioautography. These lymphocytes are present in the draining lymph nodes in a frequency of ∼50/1000 lymphocytes in animals immunized 2–4 wk earlier with DNP-GPA in complete Freund's adjuvant. Nonimmunized animals have ∼0.4 DNP-GPA antigen-binding cells (ABC) per 1000 lymphocytes. An increase in the frequency of DNP-GPA ABC in peripheral blood is detectable by 5 days after immunization, which is before the time that serum anti-DNP antibody is measurable.

The receptors of these ABC are hapten specific in that free ϵ-DNP-L-lysine, at low concentration, inhibits the binding of DNP-GPA-125I; DNP bovine serum alumbin (DNP-BSA) is equivalent to DNP-GPA in the inhibition of binding of DNP-GPA-125I to ABC; and both DNP-GPA agarose beads and DNP-BSA agarose beads specifically adsorb DNP-GPA-125I ABC. Anti-immunoglobulin antisera, particularly anti-γ2 sera, inhibit the binding of DNP-GPA-125I to these cells implying that the receptors are immunoglobulin, primarily of the γ2 heavy chain class.

DNP-GPA-125I ABC appear to represent precursors of antibody-secreting cells and have specificity characteristics which are very different from cells, of similarly immunized guinea pigs, which mediate a cellular immune response to DNP-GPA.

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