Tumor necrosis factor-beta (TNF-β), also known as Lymphotoxin-alpha (LT-α), is a cytokine produced by lymphocytes. TNF-β mediates a large variety of inflammatory, immunostimulatory, and antiviral responses. TNF-β is also involved in the formation of secondary lymphoid organs during development and plays a role in apoptosis. In TNF-β knockout mice, all Peyer’s patches and lymph nodes will fail to develop indicating TNF-β’s importance in immunological development.