Demonstration of a helper factor(s) with T-cell-replacing activity in synovial fluid

Cell-free synovial fluid (SF) obtained from patients with rheumatoid arthritis contains a helper factor(s) capable of augmenting the generation of plaque-forming cells (PFC) in pokeweed mitogen (PWM)-stimulated normal peripheral blood mononuclear cells (PBMC). This helper factor behaves like a polyclonal B-cell activator, in that it triggers the formation of IgM, IgG, and IgA PFC. However, SF has little or no effect on the proliferation of PWM-activated PBMC. Furthermore, SF was capable of replacing T cells for PWM-induced differentiation but not proliferation of enriched human blood B lymphocytes. No helper factor or T-cell-replacing activity was found in SF from patients with traumatic synovitis. Fractionation of SF containing helper activity on staphylococcal protein A column indicated that the activity is induced by biologically active molecules distinct from materials that preferentially bind to protein A such as IgG immune complexes. We conclude that the present activity has striking similarities to the recently described B-cell differentiation factor that is produced by specifically activated T-cell lines in vitro.