The variable regions of immunoglobulin (Ig) k and λlight chain genes of the B-cell lines derived from peripheral blood of a rheumatoid arthritis patients were investigated. B-cell lines, C1, D4, E2, E5 and G7 were generated and variable regions
of
Ig
light chains were amplified by an C1.2, D4.5 and E5.3 were 95.9% and 98.8% identical to Vd, O2/O12 and L12 a germline genes of the VkI subgroup, respectively. The Jk2 joining segment was utilized in the C1.2 and the Jk1 in D4.5 and E5.3. An
interesting
finding is that there was a 6 nucleotide insertion in the leader sequence of D4.5 compared tot he O2/O12 gene. The 6 nucleotides are probably derived from the leader intron sequence at the 3' intron-exon border.
E2 and G7 produced λlight chains. The VL region of E2.4 and E2.6 clones had the highest homology (96.1% and 97.2%, respectively) to the IGLV6S1 germline gene and each VL gene segment was juxtaposed with the Jλ2/Jλ3 gene. In the G7.1 λ light
chain
the Humlv117d germline gene of a VλI subgroup and the Jλ2/Jλ3 joining segment were utilized without any mutation. In the G7.4, there were 7 base differences when compared with the germline sequence (98.2% homology).
Among seven analyzed VL clones, six were mutated. Overall mutation rates of VL regions in the 6 mutated clones, C1.2, D4.5, E2.4, e2.6, E5.3 and G7.1, varied from 0.3% to 2.8%, and the extent of mutation in CDR was higher than that in FR(average
4.0% vs
0.9%). Especially, in E2.4 and E2.6 VL regions, the mutation rates in CDR(5.7%~6.9%) were over 15 fold higher than that in FR(0.4%). In these clones, R/S ratios in CDR were 4-5, indicating that the E2.4 and E2.6 VL regions underwent the process
of
affinity maturation. However, the R/S ratio in CDR of other VL clones were less than 2.9, suggesting that these VL clones did not undergo the process of affinity maturation.
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