Thymulin
A nonapeptide (9 amino acids) naturally secreted by thymic epithelial cells that requires zinc binding for full biological activity. Distinct from Thymalin (which is a thymic extract mixture). Plays a central role in T-cell maturation, immune system regulation, and maintenance of the zinc-thymulin axis that declines with aging. Thymulin levels decrease as the thymus involutes with age, contributing to immune senescence.
Typical Dosage
Research: 1-5 mg subcutaneous once daily. Anti-aging protocols: 1 mg subcutaneous once daily for 10-20 day courses. Zinc supplementation (15-30 mg zinc daily) recommended for full biological activity. Courses repeated 2-3 times yearly.
Administration
Subcutaneous injection
Mechanism of Action
Thymulin (also known as facteur thymique sérique, FTS) is a nonapeptide (Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) that is unique among thymic hormones in requiring a zinc ion for biological activity. The zinc ion is coordinated by the asparagine (position 9), serine (position 4), and the N-terminal glutamic acid, creating a metallopeptide complex where the zinc is essential for the correct three-dimensional conformation needed for receptor binding. Without zinc, thymulin is biologically inactive — this zinc dependency has important implications for immune function in zinc-deficient individuals.
Thymulin is produced exclusively by thymic epithelial cells and is the only thymic hormone that is truly thymus-specific — its serum levels become undetectable after thymectomy (surgical thymus removal). It binds to high-affinity receptors on T-cell precursors (thymocytes) and mature T cells, promoting several key aspects of T-cell biology. It induces the expression of T-cell differentiation markers (CD2, CD3, CD4, CD8), driving immature thymocytes through the stages of T-cell maturation. It enhances the cytotoxic function of CD8+ T cells and the helper function of CD4+ T cells. It modulates the balance between T-helper and T-suppressor (regulatory) cell populations, promoting appropriate immune regulation.
Thymulin also modulates cytokine production — it promotes IL-2 secretion (essential for T-cell proliferation and the generation of effector T cells), enhances IFN-γ production (important for Th1 cellular immunity), and influences the balance of pro-inflammatory versus anti-inflammatory cytokines. Serum thymulin levels peak around puberty and decline progressively with age, becoming virtually undetectable by age 60 — mirroring the age-related involution of the thymus gland. This decline correlates closely with immunosenescence markers: reduced naive T-cell output, skewed CD4/CD8 ratios, impaired vaccine responses, and increased susceptibility to infections and cancer. Zinc supplementation alone can partially restore thymulin activity in zinc-deficient elderly individuals, highlighting the clinical importance of the zinc-thymulin interaction.
Regulatory Status
Not FDA approved. Naturally occurring hormone. Research-grade available from peptide suppliers. Studied for immune reconstitution and anti-aging applications.
Risks & Safety
Common: injection site reactions, mild fatigue. Serious: very limited human clinical data for supplemental use, requires adequate zinc status for activity (inactive without zinc), potential immune overstimulation in autoimmune conditions. Rare: allergic reactions. Generally well tolerated in available data. Not FDA approved.
Research Papers
3Published: December 11, 2025
Abstract
Development of neutralizing anti-factor [F]VIII antibodies (inhibitors) follows recognition by CD4+ T cells of epitopes that are presented on the individual's human leukocyte antigen (HLA) class II. Limited blood volumes have presented a major challenge in mapping T-cell epitopes in FVIII, especially as these immune responses typically develop in early childhood.
Published: October 30, 2025
Abstract
Osteoporosis is a prevalent metabolic bone disorder that significantly impairs patients' quality of life. Mounting evidence suggests a close relationship between systemic inflammation and bone metabolism, yet the causal nature of this association remains unclear. This study aims to elucidate potential causal links between circulating inflammatory factors and osteoporotic pathological fractures. We employed a bidirectional 2-sample Mendelian randomization (MR) approach, utilizing large-scale genetic data from the FinnGen biobank (1822 osteoporosis cases and 3,11,210 controls) and the genome-wide association study catalog to analyze 91 circulating inflammatory factors. Instrumental variables were selected using a threshold of P < 1 × 10-5, followed by stringent linkage disequilibrium pruning (R2 < 0.001). The inverse variance weighted method served as the primary analytical tool, supplemented by MR-Egger, weighted median, and mode-based estimator methods. Sensitivity analyses, including leave-one-out analysis, Mendelian Randomization Pleiotropy RESidual Sum and Outlier, and Cochran's Q test, were conducted to assess the robustness of the results. Forward MR analysis identified potential causal associations between 7 inflammatory factors and the risk of osteoporotic pathological fractures. Notably, Artemin levels were negatively correlated with fracture risk (OR = 0.7954, P = .0167), while elevated levels of β-nerve growth factor (OR = 1.2375, P = .0398), C-X-C motif chemokine 10 (OR = 1.2675, P = .0183), CXCL6 (OR = 1.2623, P = .0026), interleukin-10 receptor α subunit (OR = 1.2828, P = .0204), interleukin-10 receptor β subunit (OR = 1.1463, P = .0386), and latency-associated peptide transforming growth factor β1 (OR = 1.2481, P = .0206) were associated with increased fracture risk. Reverse MR analysis suggested that fractures might lead to decreased levels of C-X-C motif chemokine 11 (OR = 0.9574, P = .0104), interleukin-1α (OR = 0.9591, P = .0263), and thymic stromal lymphopoietin (OR = 0.9625, P = .0439), as well as elevated levels of tumor necrosis factor-β (OR = 1.0519, P = .0111). This study unveils a complex bidirectional relationship between circulating inflammatory factors and osteoporotic pathological fractures. These findings provide novel insights into the pathogenesis of osteoporosis and offer important clues for potential preventive, diagnostic, and therapeutic strategies.
Published: May 20, 2025
Abstract
Myasthenia gravis (MG) is an autoimmune disease most frequently caused by autoantibodies (auto-Abs) against the acetylcholine receptor (AChR) located at the neuromuscular junction. Thymic follicular hyperplasia is present in most of the patients with early-onset AChR-Ab+ MG (EOMG), but its cellular and molecular drivers and development remain poorly understood.
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