Ultrastructural examination of the spleen after respiratory and general antigenic stimulation

An ultrastructural study was carried out on the spleen of white rats stimulated repeatedly by respiratory and intramuscular ways with suspensions of living pneumococci and respectively with killed germs in complete Freund adjuvant. A high number of immunoblasts rich in polyribosomes populate the periphery of hypertrophied lymphoid follicles organized in multiple layers. Around the periarteriolar sheaths, mainly in systemically stimulated animals, there were evidenced activated lymphocytes with clear cytoplasms, dispersed monoribosomes and moderately developed mitochondria, concentrated at a cell extremity. Clusters of blastic and mature plasma cells, the cytoplasm of which is almost entirely occupied by rough endoplasmic reticulum, dominate the red pulp structure. Contacts between lymphocytes and histiocytes and an intense activity of macrophages complete the electron microscopic picture of the spleen immune response.