Physiological significance of thymic B lymphocytes: An appraisal

Recent observations suggest that minor cell populations located in the thymus play critical roles in T-cell development and T-cell repertoire selection (Moller, 1988). Although known for a long time (Miller and Osoba, 1967), little attention has been paid to intrathymic B lymphocytes (TBL). This subpopulation is found throughout life, and represents 0.1–1% of all “thymocytes” and up to 30–60% of the intrathymic cells left after negative selection with anti-Thy-1 antibodies (Isaacson et al., 1987; Miyaba-Inaba et al., 1983; Andreu et al., submitted). In the past, thymic B lymphocytes (TBL) have been considered as “recirculating” B cells, and their thymus localization as being devoid of particular significance. However, their presence at very early ontogenic stages, as well as the appearance of subclasses of antibody-secreting cells in newborn thymuses before any other lymphoid tissues (table I), and other findings discussed below suggest their specific localization and physiological role inside the thymus.