Density distribution analysis of a primary antibody forming cell response.

The technique of equilibrium density gradient centrifugation has been used to study the antibody forming cells (AFC) produced in the Lewis rat and the toad in response to polymerized flagellin protein antigen. In both animals the AFC at the peak of the response were heterogeneous in density, and formed many separate peaks, as has been observed previously with sheep erythrocyte antigen. Two lines of evidence suggested the various peaks were of biological significance. The earliest AFC found in the rat spleen were simpler in density profile than the AFC at the peak, although a complex `steady-state' situation developed soon after. In the toad, a definite sequence of density peaks appeared progressively during the whole response. In the rat, the AFC making different classes of antibody gave different density profiles, and could be partially separated from each other. The density separation technique may be useful for studying the differentiation and maturation of antibody forming cells.