The lymphotoxin (LT)-beta heterotrimer was recently identified as a molecule containing LT-alpha subunits, tethered to the cell through non-covalent association with an integral plasma membrane protein, derived from the LT-beta gene. Since knockout mutations of the LT-alpha gene yield animals that lack lymph nodes, whereas animals lacking either or both of the receptors for tumor necrosis factor (TNF) and LT-alpha homotrimers have normal lymph nodes, it has been inferred that the association between the LT-beta heterotrimer and its cognate receptor is required for lymph node ontogeny. Similarly, LT-beta and its receptor are thought to be important for development of the spleen. Since LT-alpha deficient mice lack lymph nodes, it is difficult to assess the extradevelopmental contribution of LT-beta to immune competence. To this end, we employed a strategy for the conditional blockade of LT-beta heteromer activity in normal mice. The interaction between LT-beta and its receptor is essential for the destruction of intracellular Listeria monocytogenes.