A human monoclonal IgA rheumatoid factor using the VkIV light chain gene.

A human hybridoma stably secreting IgA rheumatoid factor (RF) was produced by cell hybridization with peripheral blood lymphocytes of a patient with rheumatoid arthritis. The RF was of the IgA1 isotype with kappa-light chains and was useful for standardization or specificity controls in class-specific RF assays. RF activity was detected only when the IgA molecular were in a polymeric state, and could be measured by enzyme linked immunosorbent assay as well as in conventional agglutination based tests. The RF had the modified Ga fine specificity described previously for several RFs and for protein A. The immunoglobulin V genes used were isolated and sequenced. The light chain was encoded by the VkIV gene rearranged to Jk2; compared to the published VkIV germ line gene there was 90% nucleotide homology. The heavy chain gene used belonged to the VHI family and was rearranged to JH4. Comparisons with published sequences revealed 90% homology with the recently characterized VH gene expressed by RF-TS3, a rheumatoid synovia RF hybridoma.