NEGATIVE SELECTION OF HUMAN GERMINAL CENTER B-CELLS BY PROLONGED BCR CROSS-LINKING

The antigen receptors on T and B lymphocytes can transduce both agonis t and antagonist signals leading either to activation/survival or aner gy/death. The outcome of B lymphocyte antigen receptor (BCR) triggerin g depends upon multiple parameters which include (a) antigen concentra tion and valency, (b) duration of BCR occupancy, (c) receptor affinity , and (d) B cell differentiation stages. Herein, using anti-immunoglob ulin kappa and lambda light chain antibodies, we analyzed the response of human naive, germinal center (GC) or memory B cells to BCR crossli nking regardless of heavy chain Ig isotype or intrinsic BCR specificit y. We show that after CD40-activation, anti-BCR(kappa+lambda) can elic it an intracellular calcium flux on both GC and non-GC cells. However, prolonged BCR cross-linking induces death of CD40-activated GC B cell s but enhances proliferation of naive or memory cells. Anti-kappa anti body only kills kappa(+) GC B cells without affecting surrounding lamb da(+) GC B cells, thus demonstrating that BCR-mediated killing of GC B lymphocytes is a direct effect that does not involve a paracrine mech anism. BCR-mediated killing of CD40-activatcd GC B cells could be part ially antagonized by the addition of IL-4. Moreover, in the presence o f IL-4, prestimulation through CD40 could prevent subsequent anti-Ig-m ediated cell death, suggesting a specific role of this combination in selection of GC B cells. This report provides evidence that in human, susceptibility to BCR killing is regulated along peripheral B cell dif ferentiation pathway.