DOWN-REGULATION OF L-SELECTIN SURFACE EXPRESSION BY VARIOUS LEUKOCYTEISOLATION PROCEDURES

L-selectin, a cell surface glycoprotein expressed on lymphocytes, gran ulocytes, and monocytes, has been implicated in lymphocyte homing and extravasation of phagocytic leukocytes into areas of inflammation. Con siderable differences of L-selectin expression among various individua ls has been reported, with clinical correlations to perinatal events, maturation, and circadian rhythm. In this study, L-selectin expression of various white blood cells was found to be differentially sensitive to ficoll-hypaque or percoll density gradient centrifugation. After d ensity gradient centrifugation, a significant loss of median monocyte L-selectin expression was observed when compared to time and temperatu re-matched controls or results obtained by whole blood incubation with anti-L-selectin monoclonal antibodies followed by simultaneous leukoc yte fixation and red cell lysis. Mock treatment itself was associated with a variable L-selectin loss of monocytes but not lymphocytes or gr anulocytes. Ficoll-hypaque or percoll density gradient centrifugation resulted in significant L-selectin down-regulation of lymphocytes whil e granulocytes separated from lymphocytes and monocytes by ficoll-hypa que or percoll retained full L-selectin surface reactivity. L-selectin downregulation was seen also after colloid sedimentation with hydroxy -ethyl starch. It is concluded that unseparated blood should be used f or measuring L-selectin expression.