An ultrastructure study on antibody production of the lymph nodes of rats with special reference to the role of germinal centers.

Antibody-containing cells in lymph nodes, expecially in germinal centers, and in thoracic duct of rats sensitized by injection of horseradish peroxidase were studied with the immunoperoxidase method. In the primary response the large germinal center cells began to produce antibody on the 9th day and predominated thereafter in germinal centers ,added by intercellular antibody deposition in its late stage. The "ordinary" medium-sized germinal center cells were a minor component. In the secondary response, the intracellular antibody positivity disappeared immediately after the antigenic rechallenge but reappeared from 6 hours later in the large germinal center cells which further transformed from 48 to 72 hours into the "specifically differentiated" medium-sized germinal center cells that disappeared by 96 hours after the secondary injection to enter the thoracic duct. Antibody-containing cells outside the germinal centers appeared 5 to 6 days after the primary injection and were mainly comprised of plasmocytic cell series which was classified into interfollicular large cells, proplasmocytes and plasmocytes. Some results conflicting with the cytological identity of both cell series were presented.