MOLECULAR CHARACTERIZATION OF MONOCLONAL IGM DERIVED FROM HUMAN B-CELL LINES EXPRESSING THE 4C9 RHEUMATOID-FACTOR ASSOCIATED IDIOTYPE

Ten human monoclonal B cell lines that express the RF associated Id 4C 9 were analyzed using an immunogenetic approach. Five of eight tested lines were also strongly positive for the 6B6.6 Id. We found that all the 4C9/6B6.6 positive lines expressed VkIIla light chain genes. In co ntrast, 4C9 reactivity was also found on a cell line expressing a VkII Ib light chain gene and on a line expressing a V light chain gene. The two anti-ids recognized a linear light chain determinant on Humkv328 encoded light chains but also a conformational determinant on Vg encod ed light chains that appeared to be dependent on the presence of a hea vy chain. Idiotypic reactivity occurred on both RF positive and RF neg ative antibodies. Within this idiotypic system, the basis for idiotypi c reactivity and RF reactivity is complex, subject to both heavy and l ight chain gene usage and sensitive to small numbers of somatic mutati ons.