Differential effect of monoclonal anti-DR antibody on monocytes in antigen- and mitogen-stimulated responses: mechanism of inhibition and relationship to interleukin 1 secretion.

A differential role for DR antigens on monocytes in antigen-stimulated as opposed to mitogen-stimulated human lymphocyte responses has been observed. A monoclonal anti-DR antibody used to treat monocytes caused inhibition of antigen-induced T-cell responses and of T-cell-dependent B-cell responses. However, anti-DR antibody treatment of monocytes did not inhibit mitogen-induced responses. Anti-DR treatment of monocytes did not induce suppression, as antigen-induced responses could be reconstituted with untreated monocytes. Anti-DR treatment of monocytes did not merely block interleukin 1 (IL-1) secretion since addition of IL-1 could not restore antigen-induced responses. Monoclonal anti-DR antibody did not directly inhibit monocyte secretion of IL-1. DR-negative monocytes, selected by antibody and complement, could not present antigen, even though they were capable of secreting IL-1. Thus, this monoclonal anti-DR antibody sterically blocks antigen presentation by monocytes without induction of suppression or inhibition of IL-1 secretion. Monocyte DR antigens appear essential for stimulation of antigen-induced responses, but DR antigens on monocytes may not be essential for mitogen-stimulated responses and do not appear to be related to the ability of monocytes to secrete IL-1.