Vitamin D Modulates Humoral Responses to SARS-CoV-2 Vaccination in Autoimmune Thyroiditis: An Endocrine–Immune Perspective Supported by Network Pharmacology, Molecular Docking, and Molecular Dynamics Simulations

Autoimmune thyroiditis (AIT) is characterized by dysregulated endocrine-immune interactions, and vitamin D has been proposed as a potential immunomodulatory factor influencing vaccine-induced immune responses. This study investigated the association between serum vitamin D status and humoral responses to SARS-CoV-2 vaccination in patients with AIT, while exploring potential molecular mechanisms using network pharmacology, molecular docking and Molecular Dynamics (MD) simulations. Patients were stratified according to serum 25-hydroxyvitamin D levels as deficient, insufficient, or sufficient. Anti-spike receptor-binding domain (RBD) IgG titers, thyroid autoantibodies, and thyroid-stimulating hormone levels were measured. In parallel, vitamin D₃ related molecular targets were integrated with AIT-associated genes, followed by protein-protein interaction analysis, molecular docking and MD simulations were performed to assess the interactions between vitamin D₃ (cholecalciferol) and selected key proteins. An inverse correlation was observed between serum vitamin D levels and anti-RBD IgG titers (<i>p</i> = 0.0013), with higher antibody responses detected in vitamin D-deficient patients. Network pharmacology analysis highlighted CYP19A1, CYP17A1, and ESR1 as prioritized targets associated with steroid hormone biosynthesis and endocrine signaling pathways. Molecular docking showed compatible binding of vitamin D₃ to these proteins, while MD simulations supported the structural stability of the complexes over time. Collectively, these findings suggest that vitamin D status may influence post-vaccination humoral immune responses in AIT, potentially through modulation of endocrine-immune crosstalk. Further longitudinal and mechanistic studies are required to clarify causality and clinical relevance.