Lyb-2 system of mouse B cells. Evidence for a role in the generation of antibody-forming cells

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Abstract
The Lyb-2 cell-surface alloantigens of the mouse are selectively and perhaps exclusively expressed in the B lymphocyte lineage, but not on antibody-forming cells. Thus if the Lyb-2 molecule is concerned in specific B cell function, it must participate in the antibody response generative phase. Monoclonal Lyb-2 antibody was found to depress the plaque-forming cell (PFC) response to sheep erythrocytes in 5-day Mishell-Dutton assays when added within the first 3 days of culture, but not later. The PFC generation rate was not affected, signifying an absolute reduction in the number of PFC generated. Because reduction of PFC counts by Lyb-2 antibody was not affected by exclusion of Lyt-2+ T cells, it is unlikely that the reduction depends on augmented suppression by T cells. Augmented B cell-mediated suppression is also unlikely, because the PFC response of serial combinations of congenic Lyb-2.1 and Lyb-2.2 cells, in the presence of monoclonal Lyb-2.1 antibody, was reduced only in direct proportion to the number of Lyb-2.1 cells present. The PFC response of Lyb-2.1/Lyb-2.2 heterozygous cells was not reduced by Lyb-2.1 antibody, presumably because PFC generation is impeded only if most Lyb-2 sites are blocked. Further evidence that the molecule identified by Lyb-2 plays a critical role in antibody-forming cell (AFC) generation in response to T-dependent antigen is that Lyb-2 antibody does not reduce the PFC response to the T-independent antigens trinitrophenylated (TNP) Brucella abortus and TNP-Ficoll, although elimination of Lyb-2+ cells from the starting population by Lyb-2 antibody and complement reduces the PFC response to T-dependent and T-independent antigens alike.