Intracellular distribution of antibody in immunocytes responding to secondary challenge with horseradish peroxidase

A new improved immunoperoxidase method was used to study the antiperoxidase antibody-forming cells (AFC) in the medullae of mouse popliteal nodes after a second challenge with horseradish peroxidase (HRP). Two populations of AFC were found: a) A stable nondividing background population of mature plasma cells whose content of antibody increased 3 days after challenge and b) A new population of cells which increased in number exponentially between 18 hours and 5 days after challenge. In contrast with the first response, the new AFC included many stimulated lymphoid cells, significant numbers of small lymphocytes, and plasma cells. The results suggest that the morphology of the AFC found in the first and second responses reflects the stage in their developmental cycle at which the precursor cells are recruited into the AFC population. More than 90% of the AFC arising between 18 hours and 3 days after challenge had antibody in their perinuclear cisternae, and their cisternae of rough endoplasmic reticulum were rapidly filled with antibody. The striking differences between the intracellular localisation of antibody during the first and second responses are discussed.