Thymosin is a thymic hormone that regulates pre-T cell development. It is not released from the pituitary. Antithymocyte antibodies are not thymosin but are useful in transplantation rejection therapy. Lymphokines are released from T cells, but thymosin is a thymic hormone, not a lymphokine. Ref: Kipps T.J. (2010). Chapter 5. The Organization and Structure of Lymphoid Tissues. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.