Human germinal centre B cells inhibit mitogen-induced proliferation of mantle zone B cells

Lymphoid follicles are the main B-cell areas in peripheral lymphoid tissues. These structures commonly consist of germinal centre (GC) and mantle zone (MZ) regions. In the present work, human tonsillar B cells belonging to these two compartments were purified by a combination of density centrifugation and separation techniques involving the recognition by monoclonal antibodies of specific surface molecules followed by panning and magnetic bead selection. These purified populations were identified as GC and MZ cells by three different criteria: (1) GC cells showed the phenotype IgD- CD20+bright CD38+ CD44- and peanut agglutinin (PNA)+, and MZ cells were IgD+ CD20+dim CD38- CD44+ and PNA-; (2) morphologically, MZ cells appeared as small resting lymphocytes whereas GC cells consisted of large blastic cells of the germinal centre; (3) functionally, most GC, but not MZ, cells underwent apoptosis early in culture. The isolation of GC and MZ cells allowed the study of their proliferative response. As a result of these studies, GC cells were demonstrated to inhibit the proliferation of MZ cells in response to B-cell mitogens (Staphylococcus aureus Cowan I and anti-mu plus BCGF) in a concentration-dependent way; 50% inhibition was reached at a GC/MZ cell ratio of 1/2. This effect did not require GC-cell DNA synthesis since similar results were obtained with irradiated GC cells. Neither was it due to a non-specific toxic effect since GC cells did not alter the proliferative response of autologous T cells to mitogens (phytohaemagglutin and anti-CD3). The inhibition required cellular contact between GC and MZ cells, and was not restricted by histocompatibility barriers. These data suggest the possible existence of a new regulatory pathway within peripheral B-cell areas.