AbstractThe accessory function (AF) of various B cell lines has been investigated by studying their ability to replace monocytes inducing the proliferation of highly purified T lymphocytes in the presence of phytohemagglutinin. AF could be exerted by B cells from different origin, including Epstein‐Barr virus (EBV) transformed lymphoblas‐toid cell lines (LCL), Burkitt's lymphoma (BL)‐derived lines, either EBV‐positive or not, pre‐B and B leukemias and lymphomas. The EBV‐converted BJAB‐B95 BL cells could exert an AF as efficient as BJAB cells, their EBV‐negative counterparts, which demonstrates that EBV itself does not play any role in this function. The HLA‐DR antigen‐negative BL‐K562 hybrids PUTKO and DUTKO, T51.4.1.6 cells which derived from an HLA‐DR‐negative variant of the T51 LCL and 721.84.5 cells from a mutagenically dissected HLA‐DR‐negative clone of the 721 LCL, also exerted very efficient AF. 721 LCL, PUTKO and DUTKO hybrids could produce interleukin 1 activity when triggered with 12‐0‐tetradecanoyl‐phorbol 13‐acetate (TPA). Furthermore, addition of anti‐DR monoclonal antibodies which blocked completely the AF of the B cell lines in mixed lymphocyte‐tumor cell reaction did not affect the mitogen‐triggered AF exerted by the same B cell lines. The induction of cellular differentiation with TPA markedly reduced the AF exerted by all B cell lines studied as well as by the hybrid cells DUTKO. By contrast, the PUTKO hybrid was unsensitive to sodium butyrate and TPA treatments, which were unable to abrogate its AF. Taken together, these data indicate that the AF in mitogen‐induced T lymphocyte responses is dependent upon some precise maturational stages of accessory cells and HLA‐DR antigen expression is not required
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