Antibody to horseradish peroxidase was localized by electron microscopic immunocytochemistry in cells of the popliteal lymph nodes of the rabbit after a single injection of antigen with complete Freund's adjuvant and after a second antigen administration. Synthesis of antibody, chiefly of 7S type, occurred simultaneously in two types of cells: large, clear, fixed, typical plasma cells, and small, dense, circulating cells which exhibit morphological characteristics of both small lymphocytes and plasma cells. We call the latter "lymphoplasmacytes" and propose that they arise from small lymphocytes. They secrete antibody by clasmatosis and continue to develop an elaborate endoplasmic reticulum after specific antibody synthesis ceases. In the presence of an additional antigenic stimulation, a second cycle of antibody synthesis may begin around the nucleus in the same cell, with antibody accumulating in the perinuclear space sometimes even before the previously synthesized antibody has been entirely secreted at the cell periphery. On this basis, we propose that the lymphoplasmacyte is a memory cell and that memory and antibody synthesis are two different activities of the same cell. The appearance of a small amount of 19S antibody may be correlated with the presence of a small number of antibody-containing, large lymphocytes.

This content is only available as a PDF.