Lyb3: a B cell surface antigen associated with triggering secretory differentiation

The results discussed in this review show that the TNP-specific IgA lambda 2-secreting BALB/c plasmacytoma MOPC-315 is partially composed of small lymphocytoid, presecretory cells which express the Lyb3 determinant. It is shown that MOPC-315 cell secretory differentiation, but not clonal proliferation, can be modulated by anti-Lyb3. Anti-Lyb3 serum has been shown to: 1) augment secretory differentiation enhancement by suboptimal numbers of secretory differentiation-enhancing, IgA315-specific helper T cells; 2) replace this secretory differentiation-enhancing T cell population as long as clone growth helper T cells are present; and 3) block suppression of secretory differentiation mediated by carrier-immune Ts cells. These results demonstrate that whether anti-Lyb3 serum enhances immune responses by replacing or augmenting a helper signal or by counteracting suppressor signals, the effects are focused on secretory differentiation events and have no effect on clonal proliferation.