Thyroid-infiltrating B lymphocytes in Graves' disease are related to marginal zone and memory B cell compartments

B lymphocytes that infiltrate the thyroid (Thy-B cells) in Graves' patients appear to be implicated in the patho-physiology of this disorder. The goal oi the present study was to examine the nature of these Thy-B cells. To th is end, Thy-B lymphocytes were isolated from surgical thyroidal samples, an d their phenotype was determined by using mouse monoclonal antibodies (mAb) directed against a wide variety of surface markers, followed by flow cytom etry multicolor analysis. The results show that most Thp-B cells (congruent to 60%) exhibited IgM(+) IgD(low) (to-) surface immunoglobulin (Ig) profil e, whereas the minor cell fraction (congruent to 30%) consisted of switched IgG(+) memory B lymphocytes. Thy-B cells expressed low levels of CD5, CD23 , and CD62L, which distinguished them from the resting B-cell pool, the maj or B-cell subset in the blood. In addition, they lacked CD38, CD10, and CD7 1, characteristic molecules for the germinal center B lymphocytes. In addit ion, Thy B lymphocytes showed peculiar patterns both of adhesion molecules (CD62L(-), CD44(intermediate)), and of activation molecules (CD69(+), CD80( +), and, in part, CD95(+)). Taken together, these results suggest that the Thy-B lymphocyte subset consists of a combination of IgM(+) B cells resembl ing marginal zone B lymphocytes, and isotype-su itched memory B cells.