Increase in the complement-fixing ability of murine IgG anti-lymphocyte antibodies by addition of monoclonal IgM rheumatoid factors.

Mouse monoclonal IgM anti-IgG autoantibodies (rheumatoid factors) markedly enhanced the complement fixing ability of 2 murine IgG1 monoclonal antibodies against human lymphocytes (anti-Leu 4 and T305). The IgM rheumatoid factors were effective when added simultaneously with the monoclonal anti-lymphocyte antibodies, and were not themselves toxic towards human lymphocytes. Monoclonal IgM rheumatoid factors are simple reproducible reagents for amplifying complement fixation by murine IgG hybridoma antibodies.