Since the putative primary cleavage site of human CD62L was identified, we cloned wild type and a shedding resistant mutant dK-S into lentiviral vectors to directly test for an association between CD62L and CD107a. In all of our assays, the dK-S mutant was almost Z-VAD-FMK completely resistant to activation induced shedding. The cytoplasmic tail of CD62L is highly basic and consists of only 17 amino acids that have been reported to regulate shedding, microvillus positioning and the tethering/rolling. Specifically, the cytoplasmic tail of CD62L has been reported to interact with at least three different proteins including calmodulin, a-actinin family of membranecytoskeleton cross-linkers), and protein kinase C isoenzymes. Disruption of these interactions may reduce the shedding or inhibit tethering/rolling efficiencies in vitro. In this study, we found the shedding of CD62L from the surface of T cells was antigen specific, and CD107a surface expression could only be detected in cells that had shed CD62L. Moreover, when we introduced a shedding resistant mutant of CD62L into T cells, this not only blocked CD62L shedding but also affected the surface expression of CD107a and this correlated with a downgraded ability of these cells to lyse targets. Thus our data suggest that there is a link between the shedding of CD62L and the acquisition of T cell lytic ability. As the cytoplasmic tail of CD62L interacts with molecules such as a-actinin, and a-actinin can interact with the cytoskeleton, we hypothesize that the abolishment of CD62L shedding from the T cell surface could ultimately affect the cytoskeleton structure, which in turn may disrupt the mobilization of cytotoxic granules to the cell surface and release of perforin and granzyme B to initiate target cell lysis. It is interesting to note that, in the case of ex vivo cultured murine lymphocytes used for adoptive immunotherapy to treat B16 melanoma, extended culture periods result in loss of CD62L expression and this is correlated with decreased effectiveness in vivo. This observation has been used to support the hypothesis that terminally differentiated T cells are less effective anti-cancer cells. Our date would further suggest a potential biochemical link between the loss of CD62L and decreased effector functions. Clearly the immune system maintains a balance between T cell homing to sites of infection/inflammation and effector function, and our data suggest that one of the main trafficking molecules, CD62L, may also be involved with the acquisition of effector cell function.