Thymulin (also known as Facteur Thymique Serique or FTS) is a naturally occurring nonapeptide (pyro-Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) produced exclusively by thymic epithelial cells. It is the only thymic hormone that requires zinc for biological activity — thymulin circulates in a zinc-bound active form and a zinc-free inactive form, and the balance between these forms reflects both thymic function and zinc nutritional status. Thymulin is a key regulator of T-cell maturation and function, and its production declines progressively with age as the thymus undergoes involution (shrinkage), contributing to the immunosenescence that characterizes aging.

Thymulin binds to specific receptors on T-cell precursors and mature T-cells, modulating their differentiation, maturation, and functional competence. In the thymus, it guides the differentiation of CD4+ and CD8+ T-cell lineages, ensuring proper MHC restriction and self-tolerance. In the periphery, thymulin enhances mature T-cell cytotoxicity, natural killer (NK) cell activity, and cytokine production. It also modulates the CD4+/CD8+ T-cell ratio — a critical parameter of immune competence that shifts unfavorably with age and physiological stress. Research has identified additional effects on the hypothalamic-pituitary-adrenal (HPA) axis: thymulin modulates ACTH and cortisol production, suggesting a bidirectional communication between the thymus and the neuroendocrine system.

The research literature documents thymulin's effects on immune reconstitution, infection resistance, and immunosenescence reversal. Studies in aged animal models show restoration of T-cell-mediated immune responses, improved vaccination efficacy, and enhanced clearance of intracellular pathogens. Research in the context of physiological stress (intensive training, caloric restriction, chronic illness) demonstrates that thymulin supplementation can counteract the immunosuppression associated with these states. The zinc-dependency of thymulin also means that zinc-deficient individuals (a common micronutrient deficiency) may have functionally low thymulin activity even with adequate thymic tissue.

Thymulin is suited for researchers investigating immune optimization, thymic function, immunosenescence, T-cell biology, and neuroimmune communication. It is particularly relevant for researchers studying immune function in the context of aging, intensive physical training, or chronic stress — conditions where thymic output and T-cell competence are compromised.

Reconstitute the 10mg vial with 1-2ml bacteriostatic water. Administer via subcutaneous injection, typically 1-5mg per day. Ensure adequate zinc intake in research protocols, as thymulin requires zinc for activation. The half-life of thymulin is approximately 20-30 minutes in plasma, supporting once-daily dosing for sustained immune modulation. Protocols typically run 4-12 weeks. Store at 2-8C after reconstitution. Lyophilized powder should be refrigerated and protected from moisture.