PHENOTYPIC AND FUNCTIONAL-HETEROGENEITY OF THE IGD- B-CELL COMPARTMENT - IDENTIFICATION OF 2 MAJOR TONSILLAR B-CELL SUBSETS

Two major B cell subpopulations were identified in the IgD- compartmen t of tonsils and subsequently isolated. They displayed the following p henotypes: CD10+CD38+CD44- (CD38+ B cells) and CD10-CD38-CD44+ (CD38- B cells). Of the CD38- B cells, 70% also expressed CD24 and CD39, wher eas CD77 was specifically distributed on 40% of CD38+ B cells, suggest ing an additional level of heterogeneity in the cellular composition o f these two B cell types. Whereas the majority of CD38+ B cells were i n cycle, most CD38- B cells were quiescent. Conversely, Bcl-2 was expr essed in CD38- B cells but was not detected in CD38+ B cells. Of the C D38- B cells, 30% bore the homing receptor Leu-8/Mel-14, whereas CD38 B cells lacked this marker. Thus, CD38- B cells have both survival ca pacity and migratory competence. Both subsets expressed surface (s) Ig s which were mainly of the IgG class, implying that most of these cell s have already undergone isotype switching. CD38- B cells proliferated vigorously and produced large amounts of IgG in response to cytokines , following ligation of slgs or CD40. In contrast, CD38+ B cells were only stimulated for DNA synthesis by a combination of IL-4 and anti-CD 40 antibodies, and failed to differentiate into Ig-secreting cells reg ardless of the stimulus applied. We propose that CD38- B cells represe nt an extra-follicular mature B cell population which has been positiv ely selected and rescued from apoptosis, whereas the CD38+ B cell subs et is composed of germinal centre B cells.