The relationship between storage and secretion of specific antibody by immune lymphoid cells: ultrastructural localization of anti-peroxidase antibodies in plaque-forming cells of the rabbit popliteal lymph node.

The ultrastructure of antibody-forming cells (AFC) has been studied in the lymph node cell population from rabbits locally immunized with horseradish peroxydase (PO) incorporated in complete Freund's adjuvant, and the kinetics of AFC development followed from day 7 to day 18 after one injection of PO. Identification of the AFC was done by local hemolysis assay, using carboxymethyl cellulose solidifying medium and PO-coated sheep erythrocytes. AFC were thereafter transferred by micromanipulation into a Beem capsule, fixed, treated by PO for fine ultrastructure detection of anti-PO antibodies, included, sectioned and studied by electron microscopy. It was found that the AFC were essentially of three categories: lymphocytes, proplasmacytes and plasmacytes, with (+), or without (-), intracellular antibody. The proportion of these categories varies with the time elapsed since the injection of antigen and with the plaque-forming activity of the population: lymphocytes (-) are relatively more numerous (over 30%) at the early stages of immunization (day 7). The number of plasmacytes increases with immunization. If most of them contain intracellular antibody at the early stages (up to day 9), the proportion of plasmacytes (+) decreases markedly afterwards. The cell type distribution is compatible with the idea that the lymphocytes are the precursors of plasmacytes, proplasmacytes being transitional forms, but no direct filiation scheme can actually be deduced from these experiments.