Light Chain Variable (VL) Sequences of Rheumatoid Factors (RF) in Patients with Primary Sjögren's Syndrome (pSS): Moderate Contribution of Somatic Hypermutation

Abstract

We have characterized and sequenced the variable (V) region genes of the light (L) chains of 10 immunoglobulin (IgM) rheumatoid factor (RF) monoclonal antibodies (MoAb) derived by the hybridoma/Epstein-Barr virus (EBV) technique from the peripheral blood of patients with primary Sjögren's syndrome (pSS). Six out of 10 RFs used lambda (λ) L chains, while four RFs used kappa (κ) L chains. Five out of the six λ RFs were encoded by V_λ3 gene segments, the sixth one was encoded by a V_λ1 gene segment. This preferential utilization of the V_λ3 family genes suggests selective expansion of the B cell in pSS. Three of the κ RFs used V_κ3 gene segments, while the fourth used a V_κ2 gene segment. Half of the RFs were found as unmutated copies of their closest germline (GL) gene. Interestingly these RFs were previously shown to use heavy (H) chains in GL gene configuration. Three RFs have very few mutations (2–3) and only two RFs have substantial numbers of mutations (6 and 11). This also correlated with the number of mutations in the respective H chains. In contrast to RFs in normal and RA these results further suggest the somatic mutation to be of moderate importance in the generation of RF from the peripheral blood of pSS patients.