B-CELL ACTIVATION AND IG, ESPECIALLY IGE, PRODUCTION IS INHIBITED BY HIGH CD23 LEVELS IN-VIVO AND IN-VITRO

The capacity of CD23 to regulate IgE production was evaluated in both an in vitro and an in vivo system. The decreased IgE response seen in CD23 transgenic mice was confirmed and observed to occur at all anti g en doses used. In addition, purified B cells from the Tg animals in ge neral exhibited lower IgE production when stimulated with CD40L and IL -4. To examine this down-regulating activity of CD23 an in vitro model system was developed. CHO cells were transfected with CD23, ICAM-1, o r both CD23 and ICAM-1. ICAM-1 was chosen to enhance B cell-B cell int eraction. Purified resting B cells were placed into culture with the m itomycin C-treated transfected or control CHO cells and activated with IL-4, IL-5, and CD40L-CHO. A dose-dependent decrease in IgE productio n was observed with increasing cell numbers of the CHO transfectants t hat expressed CD23. The effect lasted up to Day 3 of culture. B cell p roliferation was also inhibited in a dose-dependent fashion by increas ing numbers of CD23-expressing cells suggesting a potential effect of CD23 on B cell apoptosis. In contrast, ICAM-1-transfected or CHO contr ol cells had minimal effects on either Ig production or B cell prolife ration. While IgE production was inhibited up to 95% by high numbers o f CD23-transfected CHO cells, some inhibition of IgG and IgM productio n was also seen. Finally, the mechanism of CD23-mediated inhibition of IgE production was compared with the inhibition in IgE production see n when B cells were coactivated with multivalent anti-IgD in conjuncti on with CD40L plus optimal IL-4. To this end we used RT-PCR to compare the relative levels of epsilon-germline transcripts in control cultur es and cultures coactivated by anti-IgD, CD40L, and IL-5 or activated in the presence of high levels of CD23-expressing cells. CD22 was used as an internal standard since levels change little with B cell activa tion. Coactivation strongly inhibited epsilon-germline transcript leve ls but the presence of CD23-expressing cells did not. Thus, coactivati on potentially operates prior to isotype switching, while high CD23 co culture blocks either recombination or more likely B cell differentiat ion to high Ig producers stage. Our data support the hypothesis that I L-4 induces both IgE and a controlling agent for IgE, namely, CD23. (C ) 1997 Academic Press.