Plasma cells and their precursors. I. Preexistent antibody-forming cell precursors dominate the anti-sheep red blood cell and anti-human gamma globulin IgG antibody response.

Rabbits were immunized by a single i.v. injection of SRBC or HGG and were bled serially. Sera were analyzed by IEF using the gel overlay technique to investigate clonal patterns of circulating IgG antibodies. Clonal patterns of primary-response IgG antibodies were quite stable over a period of months, showing that this response is dominated by plasma-cell precursors already present at the time of antigenic stimulation. In the late phase of the primary IgG response, new bands were occasionally observed in the antibody spectra, suggesting the presence and triggering of newly formed plasma-cell precursors. Primary-response antisera had individually unique clonal patterns. In secondary-response antisera elicited by a second single i.v. injection, the IEF spectra were found to be more complex and could be individually distinguished only with difficulty.