Growth inhibition of Epstein-Barr virus-transformed B cells by anti-HLA-DR antibody L243: possible relationship to L243-induced down-regulation of CD23 antigen expression

Among five anti-HLA class II monoclonal antibodies (mab's) tested, the anti-HLA-DR mab L243 selectively inhibited the in vitro proliferation of Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL). Saturating amounts of L243 mab induced 50% suppression of LCL growth as revealed by measuring [3H]thymidine incorporation or counting cell numbers. Preincubation for 20 hr at 37 degrees C in the presence of L243 mab dramatically reduced the expression of certain B cell-specific antigens on LCL, notably CD23 (BLAST-2, low affinity Fc epsilon receptor). In view of the known function of the CD23 antigen as a B cell growth factor receptor, we discuss the possibility that the suppressive effect of L243 mab on LCL proliferation is due to down-regulation of CD23 antigen expression.