Rat APRIL (A Proliferation-Inducing Ligand), also known as TNFSF13, is a member of the tumor necrosis factor (TNF) superfamily that plays an important role in B cell survival, plasma cell maintenance, and regulation of humoral immunity in rats (Rattus norvegicus). APRIL is produced primarily by monocytes, macrophages, dendritic cells, and certain epithelial and stromal cells, and it signals through the receptors TACI (TNFRSF13B) and BCMA (TNFRSF17) to promote B cell maturation, immunoglobulin class switching, and long-lived plasma cell persistence. In rats, APRIL contributes to mucosal immunity, IgA production, and maintenance of antibody-secreting cells within lymphoid tissues and bone marrow. Dysregulated APRIL expression has been implicated in autoimmune and inflammatory disease models, including experimental arthritis, lupus-like disease, and transplant rejection studies. In biomedical research, rat APRIL is of particular interest in models of antibody-mediated autoimmunity, chronic inflammation, and B cell–related malignancies, where modulation of APRIL signaling is investigated as a strategy to regulate pathological B cell activation and antibody production.