Lymphotoxins - a multicomponent system of growth inhibitory and cell-lytic glycoproteins

Activated lymphocytes from experimental animals and man can release materials, termed lymphotoxins , which cause growth inhibition and cell lysis in vitro. These molecules, from human lymphocytes, are glycoproteins which can be divided into five molecular weight classes. These forms are heterogeneous, for each MW class can be further subdivided into multiple charge subclasses. It is now clear certain MW classes are interrelated and form a system of cell toxins. The larger classes (greater than 140,000 d) are associated with nonclassical antigen-binding receptors (R), which can be of T cell origin. The smaller forms (less than 90,000 d) do not express R function and are derived from the larger forms, possibly by enzymatic action. Two MW classes, one receptor-associated and one non-receptor associated, have been purified to homogeneity and their peptide composition is being studied. Functional studies reveal the larger MW forms derived from alloimmune cell populations; can induce selective and nonselective destruction of cells in vitro. Antibodies which inhibit the in vitro cell lytic ability of various human LT forms can block different classes of human lymphocyte cell killing reactions in vitro.