DIFFERENCES IN MUTATIONAL PATTERNS BETWEEN RHEUMATOID FACTORS IN HEALTH AND DISEASE ARE RELATED TO VARIABLE HEAVY-CHAIN FAMILY AND GERM-LINE GENE USAGE

The sequences of the heavy chain variable (V-H) Segment and dissociati on constants (K-d) Of 14 IgM rheumatoid factors (RF) derived from 11 d ifferent germline gene segments from five healthy immunized donors (HI D) are described. We extend a previous analysis of two clones from one donor using only the germline segment DP-10. In the present study, th e mutation patterns of these new RF and the two earlier reported HID R F clones are analyzed in relation to V-H family, germ-line origin, and K-d. The panel of HID RF is further compared with 33 previously descr ibed IgM RF from patients with rheumatoid arthritis (RA). These is a h igh rate of mutation in the panel of HID RF (mean of ten mutations/V-H ) RF originating in RA patients have a comparable mutation rate (mean of 11 mutations/V-H), suggesting that hypermutation of IgM RF is not d isease related. The HID RF have, however, a significantly lower affini ty for IgG than the RA RE We found that the structural basis of the di fferences between HID and RA RF is related to V-H family usage. RF of the V(H)1 family use very similar germ-line genes in HID and RA patien ts. HID RF of the V(H)1 family have, however, a low ratio of replaceme nt-to-silent (R:S) mutations of only 0.41 in the heavy chain complemen tarity region (CDR(H)) 1 and 2. This is statistically significantly lo wer than the corresponding ratio of 3.14 in the V(H)1 RA RE In contras t, RF of the V(H)3 family from HID and RA patients have very similar R :S ratios of 1.75 and 1.71 in CDR(H)1 and 2, respectively. The V(H)3 R A RF are, however, predominantly encoded by genes not encoding any HID RE Thus, both repertoire differences and hypermutation resulting in s ignificantly lower R:S ratios can be observed in RF from HID compared with RA RF.