IgD-Fc receptors on normal and neoplastic human B lymphocytes

Lymphocytes from normal peripheral blood and human lymphoid tumours were studied for AggIgD binding. In normal blood, 2.0-3.7% of lymphoid cells bound to IgD aggregates. Using double labelling and, enrichment and depletion experiments, a subset of normal B but not T lymphocytes exhibited IgD binding. In blocking experiments, AggIgD binding was shown to be specific and Fc dependent. Likewise, B but not T derived neoplastic lymphoid clones expressed Fc delta receptors. Fc delta receptors were exclusively present on neoplastic clones that also expressed SmIgD. Neoplastic lymphoid cells expressing SmIgM alone did not express Fc delta. The chronic lymphocytic leukaemia cell which typically bore membrane SmIgM and SmIgD expressed multiple FcR with specificities for IgM, IgD and IgG. In sequential surface redistribution experiments, Fc delta and Fc mu receptor-ligand binding produced the 'co-capping' phenomenon which was bidirectional in nature suggesting membrane association.