Comparative study of the histologic reactions to intravenous injections of heat-killed Pseudomonas aeruginosa and of BCG.

Intravenous injection (i.v.) of heat-killed Pseudomonas aeruginosa in mice produced histologic changes in the thymic cortex, some of which resembled, while others differed from, those produced by i.v. injection of living BCG. The changes that were similar consisted of pyroninophilia of cortical lymphocytes and hyperplasia of epithelial cells in the medulla and at the corticomedullary junction with increased PAS positive cells and secretions. Major differences, however, in the sequence and nature of the histologic events were observed. Pseudomonas injections produced thymic epithelial cell hyperplasia with increased PAS positive cells and secretions and pyroninophilia of thymic cortical lymphocytes earlier than did i.v. BCG (day 1 versus day 7). Corticomedullary inversion of thymic structure and early transient hyperplasia of the thymus dependent areas in the lymph nodes and spleen occurred after Pseudomonas but not after BCG injections. Hyperplasia in the B cell areas and germinal centers started to appear at day 10 after injection of Pseudomonas and persisted up to day 21 (compared to day 7 and day 14, respectively, for BCG). In contrast to i.v. BCG, Pseudomonas injections did not produce granulomas or macrophage proliferations.