Tumor necrosis factor (TNF) and lymphotoxin-alpha (LT-alpha, also known as TNF?beta) are members of a family of secreted and cell surface cytokines that participate in the regulation of immune and inflammatory responses. LT-beta (lymphotaxin-beta or tumor necrosis factor C) is a type II membrane protein with significant homology to TNF, LT-alpha, and the ligand for the CD40 receptor. LT-alpha is present on the surface of activated T, B, and LAK cells as a complex with the 33 kda glycoprotein, LT-beta. LT-beta, also expressed by active lymphocytes, forms a heterotrimer with LT-a on the cell surface and anchors LT-alpha to the cell surface. A TNF receptor-related protein, the LT-beta receptor (also known as TNFC receptor), is the human receptor for the LT-alpha/LT-beta heterotrimer. There are two LT-beta isoforms expressed in human lymphoid cell lines and non-Hodgkin's lymphomas. The gene which encodes LT-beta maps to the major histocompatibility complex region on human chromosome 6p21.3.