Synthesis of specific IgG idiotypes by rheumatoid synovium

Synovial tissue samples from 6 patients with rheumatoid arthritis were cultured, and the IgG antibodies isolated from the synovial culture supernatants were used to immunize rabbits to make 6 antiidiotypic (anti-Id) antibody preparations. After extensive adsorption, the rabbit anti-Id were tested in a solid-phase enzyme-linked immunosorbent assay (ELISA). Each anti-Id reacted predominantly with the immunizing synovial IgG and showed almost no reactivity with either pooled normal human serum IgG or with IgG from 50 normal donors. When identical amounts of matched rheumatoid arthritis serum IgG and synovial culture supernatant IgG were probed simultaneously with the corresponding rabbit anti-Id in an ELISA, 3 of 6 pairs demonstrated an increased concentration of specific idiotypes in the synovial culture supernatant IgG. Furthermore, when these 6 matched samples were subsequently analyzed by isoelectric focusing, individual IgG antibodies in 5 of 6 synovial IgG samples revealed enhanced reactivity with the corresponding rabbit anti-Id preparations, when compared with matched serum IgG. This increased synovial concentration of specific idiotypes detected by both the ELISA and isoelectric focusing was compatible with enhanced synovial tissue synthesis of the antibodies involved. These specific Id/anti-Id reactivities were not blocked by excess normal human Fc, Fab, or F(ab')2 fragments, indicating a lack of association of the stimulating synovial antibodies with rheumatoid factors or antibodies against other IgG fragments (pepsin agglutinators).