We recently reported that the single nucleotide polymorphisms of the lymphotoxin-(LT)alpha gene, a member of the tumor necrosis factor (TNF) family, are closely related to acute myocardial infarction; however, the precise mechanism of LTalpha signaling in atherogenesis remains unclear. We investigated the role of LTalpha3, a secreted homotrimer of LTalpha, in monocyte-endothelial cell adhesion using cultured human umbilical vein endothelial cells (HUVEC). We found that LTalpha3 induced cell adhesion molecules and activated NF-kappaB p50 and p65. LTalpha3 also induced phosphorylation of Akt, phosphorylation and degradation of IkappaB, nuclear translocation of p65, and increased adhesion of THP1 monocytes to HUVEC. These effects were mediated by TNF receptor (TNFR) I and attenuated by the phosphatidylinositol triphosphate-kinase (PI3K) inhibitors LY294002 and Wortmannin. Thus, LTalpha3 mediates the monocyte-endothelial interaction via the classical NF-kappaB pathway following TNFR I/PI3K activation, indicating it may play a role in the development of coronary artery disease.