Detection of thymosin 5 in calf and mouse thymus and in nude mouse dysgenetic thymus.

Thymosin 5 was traced in calf and mouse thymuses by fluorochrome-labelled rabbit anti-calf thymosin. The presence of thymosin 5 or its individual components was found 1. in groups of cortical epithelial cells in calf thymuses and in single cortical epithelial cells in mouse thymuses. 2. In some marginal (blastema) cells of the thymus cortex of calves and 14-day-old mice. 3. In perivascular epithelial cells of the calf thymus. 4. In occasional medullary epithelial cells of the calf and mouse thymus. In all cases there was a marked alternation of entirely negative and positive cell-containing thymic lobuli. In 4 of 13 cases comparatively strong positivity was found in tightyly arranged epithelial cells in an individual acinus in the dysgenetic thymus of nude mice, the positive cases being concentrated among the youngest mice studied.