B lymphocyte subsets in Hashimoto's thyroiditis

Two B lymphocyte subsets are identified on the basis of possession or lack of a surface molecule, CD5. The CD5+ B lymphocytes synthesize autoantibodies and in the process rearrange proximal variables of immunoglobulin genes. We have here studied the proportion and absolute counts of CD5+ B lymphocytes in the peripheral blood of 31 patients with Hashimoto's thyroiditis and related the findings to their HLA phenotypes and clinical features. Although the percentage and absolute number of surface immunoglobulin-positive (B) lymphocytes was comparable in patients to those in twenty controls, % CD5+ was significantly higher in the patient group (38.1 +/- 11.6 [+/- S.D.] vs. 27.9 +/- 10.1, p = 0.009). The absolute CD5+ cells (microliters) were also higher in patients with Hashimoto's thyroiditis (77.90 +/- 37.50 vs. 55.1 +/- 29.8, p = 0.020). The proportion of CD5+ cells was even higher in HLA-DR3 positive patients (43.1% +/- 7.2, n = 13) compared to six DR3+ controls (26.17% +/- 9.7, p = 0.0005). The difference between DR3- patients and controls was not significant (28.6% +/- 10.5 vs. 34.4% +/- 13.0). As the CD5 molecule may be induced on activated B lymphocytes, this study suggests that Hashimoto's thyroiditis is associated with an increase of activated B lymphocytes engaged in autoantibody synthesis. This defect is particularly obvious in DR3+ patients.