The Accessory Molecules CD5 and CD6 Associate on the Membrane

CD5 and CD6 are closely related lymphocyte surface receptors of the scavenger receptor cysteine-rich super-family, which show highly homologous extracellular regions but little conserved cytoplasmic tails. Both mol-ecules are expressed on the same lymphocyte popula-tions (thymocytes, mature T cells, and B1a cells) and share similar co-stimulatory properties on mature T cells. Although several works have been reported on the molecular associations and the signaling pathway medi-ated by CD5, very limited information is available for CD6 in this regard. Here we show the physical associa-tion of CD5 and CD6 at the cell membrane of lympho-cytes, as well as their localization at the immunological synapse. CD5 and CD6 co-immunoprecipitate from Brij 96 but not Nonidet P-40 cell lysates, independently o