Vischer TL Werner-Favre CF Wen L Zubler RH 1988 Recently, a new culture system has been devised which leads to activation, proliferation and differentiation into antibody secreting cells of at least 90% of human peripheral blood B-lymphocytes. The system uses mutant EL-4 thymoma cells of mouse origin for B cell activation and T cell/macrophage supernatant as source of cytokines (L. Wen et al., Eur. J. Immunol. 17, 887, 1987). By an ELISA system with Fc fragments as antigen and the F(ab)2 fragment of antibodies against human IgM labelled with alkaline phosphatase, we analysed the frequencies of B cells producing IgM-RFs. The mean frequency of IgM-RF producing cells in normal controls was 1/3100 (s.d. = 0.2 log; n = 5) of circulating B cells. In 2 patients with seropositive rheumatoid arthritis (RA) the frequencies were higher (1/492; 1/262), but in 2 other seropositive patients a normal (1/5540) or even a decreased (1/20000) frequency was observed. The possible relation between circulating and synovial RF producing B cells is currently being investigated. https://sonar.ch/global/documents/230157 eng info:eu-repo/semantics/altIdentifier/doi/10.3109/03009748809096752 info:eu-repo/semantics/altIdentifier/pmid/3266359 Scandinavian journal of rheumatology. Supplement. - 1988 B-Lymphocytes Cell Count Enzyme-Linked Immunosorbent Assay Humans Immunoglobulin Fc Fragments Immunoglobulin G Immunoglobulin M Lymphocyte Activation Reference Values Rheumatoid Factor Stem Cells Quantitative analysis of precursors frequency of rheumatoid factor (RF) producing human B cells. http://purl.org/coar/resource_type/c_6501