Lysosome-Associated Membrane Proteins h-LAMP1 (CD107a) and h-LAMP2 (CD107b) Are Activation-Dependent Cell Surface Glycoproteins in Human Peripheral Blood Mononuclear Cells Which Mediate Cell Adhesion to Vascular Endothelium

Lysosome-associated membrane proteins (LAMPs) are transmembrane lysosomal glycoproteins which are detectable at the cell surface of lymphocytes in patients with scleroderma and systemic lupus erythematosus. While these proteins have been shown to mediate adhesion of tumor cells to vascular endothelial selectins, the function of LAMPs expressed at the cell surface of peripheral blood lymphocytes has not been previously examined. In the present study, the role of lamp2 (CD107b) in lymphocyte adhesion to vascular endothelium and the factors which influencein vi- trocell surface expression of both lamp1 (CD107a) and lamp2 (CD107b) are examined. Freshly isolated PBMCs and unstimulated PBMCs in the culture had low levels of cell surface lamp1 and lamp2 expression which were significantly increased following PHA stimulation (P< 0.0001). A dose-dependent response to PHA and the effect of varying concentrations of serum were defined. Kinetic analysis revealed that the majority of the increase in both lamp1 and lamp2 occurred within the first 2 hr of incubation and that a subset of PBMCs maintained expression for at least 96 hr. Incubation of cells with colchicine and cycloheximide modified the cell surface expression of these proteins. Interleukins 2, 4, 6, and 8 had only a modest effect on the degree of cell surface lamp1 and lamp2 expression, though they did significantly affect the distribution of expression among different subtypes of lymphoid cells. Under the conditions utilized in this study, cell surface LAMP expression was confined primarily to CD56+cells and to CD3+cells. Functional analysis utilizing a fluorescence-based adhesion assay revealed that cell surface lamp2 mediates adhesion of PBMCs to vascular endothelium, possibly by interacting with endothelial selectins. LAMPs likely contribute to the migration of activated leukocytes to sites of inflammationin vivo.