Splenic and Hassall's corpuscles modifications following injection of fresh BCG in the guinea-pig

The results indicated that i.v. injection of fresh BCG induced in the guinea-pig thymus a transient increase of lymphocyte mitosis associated with an epithelial hyperplasia in the cortex on day 10. Changes in the medulla were more obvious on day 15. The hyperplasia of Hassall's corpuscles and epithelial cells in the medulla reached its maximum level at a time when many lymphocyte masses appeared in the splenic red pulp and in the T area of the spleen. Evidence suggesting an active secretory function in their external cells was recorded. These findings were consistent with the hypothesis that BCG produces an increase of new lymphocytes input into the T lymphocyte cycle.