Thymosins, which act on the immune system, are secreted by the

1. The thymus is one of the endocrine glands listed here. 2. It secretes the peptide hormones called thymosins. 3. Thymosins play a major role in the differentiation of T lymphocytes. 4. That gives the immune system its cell mediated arm. _Source: syllabus Biology Ch19 'Chemical Coordination and Integration', section 19.2.6_