In dendritic cells a unique signaling pathway gives human immunodeficiency virus (HIV) a distinct advantage for its replication and subsequent infection of CD-4-positive T cells. Dendritic cells capture foreign antigens with their diverse surface receptors and present the antigens to T cells. One receptor, DC-SIGN, is both an adhesion receptor that brings dendritic cells and T cells together and the recognition receptor for HIV, yet its downstream signaling pathway is unknown.