Tumor necrosis factor beta (TNF-β), also known as lymphotoxin alpha, is a cytokine secreted by lymphocytes.TNF-β mediates many inflammatory, immunostimulatory, and antiviral responses. During developmental stages, TNF-β is also involved in the formation of secondary lymphoid organs and plays a role in apoptosis. In TNF-β knockout mice, all Peyer’s lymphoid aggregates and lymph nodes failed to develop, demonstrating the importance of TNF-β in immune development.