Abstract
Using a potent in vitro limiting dilution culture system, we have activated human peripheral blood B cells to proliferate and to differentiate into antibody-secreting cells (ASC). Under these conditions 25-100% of B cells are clonally expanded and produce IgM, IgG or IgA. Culture supernatants were tested for antibodies binding to human IgG-Fc fragments (RF), the 65-kD heat shock protein of Mycobacterium bovis (hsp60), human collagens type I, II, IV, V, transferrin, lactoferrin, albumins, and gelatine. All blood samples contained precursors of ASC (p-ASC) able to produce IgM binding to these antigens in frequencies above 0.03% of B cells. Most interestingly, a significant difference exists between rheumatoid arthritis (RA) patients and controls, concerning the relative frequencies of p-ASC able to produce monospecific or multireactive RF. Whereas most p-ASC(RF) in RA patients are monospecific (mean ratio 3.7), most p-ASC(RF) in healthy control persons are cross-reactive with at least one of five other antigens tested (mean ratio 0.2). The data suggest a disease-specific expansion of p-ASC committed to the production of monospecific rheumatoid factors.