Characterization of a novel monoclonal antibody, EIV-E12, raised against enriched splenic ellipsoid-associated cells

A monoclonal antibody, EIV-E12, was produced against ellipsoid-associated cells. In postnatal chicks, the antigen defined by EIV-E12 associated with about 90% of bursal cells and accumulated in B cell-rich areas of lymphoid organs. The antigen was expressed by many splenic cells on day 9 of embryogenesis and about 1 day later in the bursal anlage, where the cells positive for the antigen localized in close proximity to the plical epithelium. In the bursa, these early EIV-E12 cells appeared before Bu-1-positive cells and may represent a dendritic cell precursor. B cells within the developing bud acquired the EIV-E12 antigen. Immunoprecipitation studies revealed a molecular weight of 233 (nonreduced) and 205 (reduced) for the EIV-E12 antigen. These values were markedly different from the molecular weight of the antigen identified by Bu-1 but similar to that of a CB10 antigen. The CB10 and EIV-E12 MAbs exhibited some differences in cellular staining. Taken together these data suggest that EIV-E12 MAb recognizes a unique cellular population during embryogenesis.