Staining patterns for the anti-horseradish peroxidase antibody reaction in proplasma cells developing in the medulla of rat popliteal lymph nodes during the secondary response.

The development of plasma cells from lymphocytes was studied in the medulla of popliteal lymph nodes of rats during the secondary response to horseradish peroxidase (HRP). Changes in the microscopic appearance of proplasma cells were compared with changes in the intensity of the anti-HRP antibody reaction in these cells. Early proplasma cells, appearing 2 to 3 days after the injection of HRP into the footpads, were relatively small cells similar in size to lymphocytes. Their small nuclei were eccentrically located due to the one-sided enlargement of the pyroninophilic cytoplasm. The reaction for the anti HRP antibody in these cells was weak or negative. Other proplasma cells located in the same medullary cord regions showed a more intense antibody reaction. This change was correlated, in many cases, with an enlargement of the nucleus, giving the cells a blast-like appearance. Three to 6 days after the reinjection of the antigen, the medullary cords contained many mature plasma cells characterized by an intense antibody reaction. The mature plasma cells were always accompanied by proplasma cells, the latter varying in microscopic appearance (stage of development) asd staining intensities (antibody contents). The staining intensities and the microscopic appearance of proplasma cells, and the proportion of proplasma cells to plasma cells, varied in different medullary cord regions of the same lymph nodes. The staining patterns, together with the microscopic appearance of the cells, seemed to show whether antibody formation was inhibited or stimulated.