B-LYMPHOCYTIC CLONAL EXPANSION IN RHEUMATOID-ARTHRITIS

Objective, To learn whether rheumatoid factor (RF), HLA-DR4, or curren t therapy influences clonal expansion of B lymphocytes (B cells) in pe rsons with rheumatoid arthritis (RA), Methods. We measured clonal expa nsion by analysis of cell surface staining for immunoglobulin light ch ains, Double staining methods detected a B cell marker (CD 19) plus ei ther kappa or lambda on peripheral blood lymphocytes from subjects wit h RA (n = 26) and controls (n = 26), The difference between frequency histograms of surface kappa and lambda staining was determined by the Kolmogorov-Smirnov statistic D that represents the fraction of clonall y expanded B cells. Results, The mean D value in RA was over 50% highe r than in the controls [0.225 +/- SD 0.155 versus 0.144 +/- 0.025 (p < 0.0001)]. Ten subjects with RA had values exceeding mean + 2 SD for co ntrols (p = 0.0007). Mean D correlated with RF titer (Spearman's rank correlation coefficient r(Sp) + 0.53, p = 0.006). All 10 high D values were found in the RA subgroups with positive serum tests for RF and w ith the HLA-DR4 positive genotype. The channel of maximal difference b etween kappa and lambda staining was higher in the RA group than in co ntrols, showing that clonal expansion was most marked among brightly s taining cells. Patients with RA currently receiving low dose methotrex ate (MTX) tended to have higher D values than those not receiving MTX (mean 0.29 versus 0.18, respectively, p <0.025). The RA group currentl y receiving MTX had a higher frequency of abnormal D values (7 of 11 v ersus 3 of 15 not currently receiving MTX, p = 0.03), This probably re flects preferential use of MTX for severely affected individuals, Conf irmatory studies to detect clonal immunoglobulin gene rearrangements w ere attempted in selected individuals with high D values, but none was demonstrated in total leukocytic or B cell enriched fractions, Conclu sion, Findings consistent with B cell clonal expansion occur in about 40% of persons with RA, particularly in the subgroups with positive se rum tests for RF and with the HLA-DR4 genotype. However, the clonal ex pansion level must be below the sensitivity of confirmatory methods.