Rheumatoid factors in primary Sjögren's syndrome (pSS) use diverse VH region genes, the majority of which show no evidence of somatic hypermutation

Abstract

Rheumatoid factor (RF) is the most common autoantibody found in patients with Sjögren's syndrome (SS). To study the genetic origin and the mechanisms acting behind its generation we have characterized and sequenced the immunoglobulin VH genes used by 10 IgM RF MoAbs derived from peripheral blood of six female patients with pSS. We compared the structure of the RF immunoglobulin VH genes with those obtained previously from rheumatoid arthritis (RA) patients and healthy immunized donors (HID). VH1 and VH4 were each used by four RF clones, one clone was encoded by VH3 family gene and one by VH2 family gene. This distribution frequency was different from that observed in RA, where VH3 was the dominant family, followed by VH1. Eight different germ-line (GL) genes encoded the clones and all of these genes were seen previously in RA and/or HID RF. Five clones rearranged to JH6, four rearranged to JH4 and one to JH5, in contrast to RF from RA and HID, where JH4 was most frequently used. D segment use and CDR3 structure were diverse. Interestingly, three out of four VH4 clones used the GL gene DP-79 that was seen frequently in RA RF. The degree of somatic mutation in the pSS RF was very much lower than seen in RA and HID RF. All the pSS RF clones except three were in or very close to GL configuration. This indicates that there is little role for somatic hypermutation and a germinal centre reaction in the generation of RF from peripheral blood in pSS.

Fig. 1

Amino acid sequences of the V_H gene region of IgM rheumatoid factor (RF) from pSS. Closest identified germ-line genes in the V BASE and DNAPLOT are shown. Dashes denote homology, uppercase letters denote replacement mutation, whereas lower case letters denote silent mutation. The codons are numbered according to the definition of Kabat [51].

Fig. 2

Nucleotide sequences of D segment of pSS rheumatoid factors (RF) compared with the closet germ-line (GL) D segment. Upper case denotes mismatches with the GL.