Monoclonal antibody 6b6.6 defines a cross‐reactive kappa light chain idiotope on human monoclonal and polyclonal rheumatoid factors

Abstract

Mouse monoclonal antibody (MAb) 6B6.6 was raised against a cross-reactive idiotope (CRI) present on the light chains of 2 human IgM paraproteins with rheumatoid factor (RF) activity. The MAb inhibited the IgG-binding activity OF these proteins, and thus appears to react with an epitope located at or near the RFbinding site. Enzyme-linked immunosorbent assay (ELISA) and Western immunoblotting studies indicate that the 6B6.6 CRI is associated with d I I a subsubgroup light chains, is not related to the Wa, Po, and Bla RF cross-idiotypic specificities, and is clearly distinct from the dIIb-associated CRI detected by MAb 17.109. Using an ELISA, we detected 6B6.6 CRI in 59% of 107 sera and 48% of 50 synovial fluids From patients with seropositive rheumatoid arthritis (RA). However, the quantities OF CRI-positive RF were small, and the amount of CRI-positive RF did not correlate with the amount of IgM-RF. The 6B6.6 CRI was shown to occur primarily id the IgM fraction of RA sera by both chromatographic studies and isotype-specific ELISA, although small quantities appeared to be associated with IgA and IgG in some sera. The presence of 6B6.6 CRI on both monoclonal and polyclonal RF is consistent with

A somatically mutated VκIV gene encoding a human rheumatoid factor light chain

“…These investigations extend and support earlier serologic studies of fine specificities and cross-reacting idiotypes of hybridomas and serum immunoglobulins of patients with RA and healthy controls [6][7][8][9]28,29].…”

“…The cross-reacting idiotypes that characterize the light and heavy chains of paraproteins with RF activity have been demonstrated at significantly lower frequencies among RF produced by hybridomas established from synovial B cells of RA patients [6][7][8]. A greater heterogeneity of RF from RA patients is further shown by their use of different isotypes and lambda light chains in addition to kappa chains [9].…”

Structural characterization of the second major cross‐reactive idiotype group of human rheumatoid factors. Association with the VH4 Gene Family

“…To investigate the H chains used by the 6B6.6 CRIpositive RF, 5-14 and 6-10 were generated following immunization with H chains of the 6B6.6 CRI-positive RF, COR and LEW. In initial testing, both antibodies bound to intact COR and LEW, but not to a control IgM, DAU (dIIa-V,3) (8). The 2 MAb also reacted with isolated H chains, but not L chains, of the immunizing proteins, by ELISA (Figure 1).…”

“…The generation and characterization of the IgG1 MAb, 6B6.6, G6, and LCl, and the IgG2b MAb, 17-109, have been described previously (7,8,15,16). The G6 antibody (17) was donated by Drs.…”

“…These RF use a separate set of structurally related KIIIa L chains, identified by the 6B6.6 monoclonal antiidiotype (8). Based on sequence comparison, these L chains likely derive from the Humkv328 gene (9), which is preferentially rearranged in the fetal liver (10).…”