384 Subpopulation of B Cells

The functional properties of T and B lymphocytes and the nature of their participation in the immune response have been elucidated to a large extent in recent years (1). Evidence of functional heterogeneity within the T-cell compartment has been garnered by utilizing surface markers which distinguish subsets of cells (2). Although B cells also carry distinctive surface markers, evidence of functional subpopulations in the B-cell compartment is scant. B-cell heterogeneity was initially suggested by Playfair and Purves (3), who reported a differential capacity of B cells from diverse anatomical regions to synergize with T cells. Additional support can be found in fractionation studies in which cells capable of responding to T-dependent and T-independent forms of hapten-carrier conjugates were separable by velocity sedimentation (4). Our laboratory has been engaged in studies of the immune response to the azobenzenearsonate epitope in mono-, bi-, and polyfunctional forms (5, 6). Previous efforts have utilized the guinea pig as the laboratory model, since guinea pigs make vigorous cellular immune responses to small monoand bifunctional azobenzene-p-arsonate (ABA) 1 derivatives. The present communication describes the initial phases of an investigation of the murine response to polyfunctional ABA conjugates. The findings indicate that strain A/J mice make plaque-forming cell (PFC) responses to the ABA epitope only when it is presented in a T-dependent form, and that the C3 receptor is a functional marker for murine B cells which respond to many T-dependent antigens (hapten-protein conjugates). Further, C3 may be an obligatory component in the pathway that leads to these T-dependent antibody responses, but the C3 receptor is apparently unexpressed on the surfaces of B cells which make T-independ-