LOW IGG PRODUCTION BY MONONUCLEAR-CELLS FROM MARROW TRANSPLANT SURVIVORS AND FROM NORMAL NEONATES IS DUE TO A DEFECT OF B-CELLS

Low IgG production is a characteristic feature of both the immunodefic iency of recipients of bone marrow transplant (BMT) and the physiologi c immunodeficiency of newborns, We tried to determine whether this is due to a B cell defect and whether this can be corrected in vitro by I gG production-promoting cytokines CD40 ligand (CD40L) and interleukin 10 (IL-10). Highly purified circulating B cells from patients at 1 yea r after transplant, normal neonates and normal adults were cultured,vi th and without anti-mu plus CD40L plus IL-10. Proliferation was measur ed on day 4 and IgM and IgG production were measured on day 9. Prolife ration and IgM production of B cells from patients and from neonates w ere somewhat low (43-67% of normal), In contrast, IgG production by B cells from patients and from neonates was markedly low (less than or e qual to 13% of normal), Decreased IgG production correlated with decre ased percentage of B cells negative for membrane IgD (mIgD). We conclu de that the low IgG production of normal neonates and patients at 1 ye ar after transplant is, at least in part, caused by a defect of circul ating B cells and that this defect cannot be corrected by CD40L and IL -10, Quantitative deficiency of switched (mIgD(-)) B cells probably ac counts for this defect.