Soluble L-selectin is present in human plasma at high levels and retains functional activity.
L-selectin expressed by granulocytes, lymphocytes, and monocytes is responsible for initial leukocyte attachment to inflamed endothelium and high endothelial venules of peripheral lymph nodes. After leukocyte activation in vitro, L-selectin is rapidly shed from the cell surface. In this study, shed L-selectin (sL-selectin) from both lymphocytes and neutrophils was demonstrated to be present in high levels in human plasma by Western blot analysis and using a quantitative ELISA. In serum from normal human blood donors, a mean sL-selectin level of 1.6 +/- 0.8 micrograms/ml (n = 63) was found by ELISA. In addition, semipurified sL-selectin from plasma inhibited L-selectin-specific attachment of lymphocytes to cytokine-activated endothelium in a dose-dependent manner. L-selectin-dependent leukocyte attachment was completely inhibited at sL-selectin concentrations of 8-15 micrograms/ml, while physiological concentrations of sL-selectin caused a small but consistent inhibition of lymphocyte attachment. sL-selectin in plasma also inhibited anti-L-selectin mAb (2-5 micrograms/ml) binding to the surface of leukocytes. Interestingly, one epitope present within the EGF-like domain of L-selectin was lost in sL-selectin, suggesting a conformational change in the structure of the receptor after shedding. The presence of serum sL-selectin with functional activity indicates a potential role for sL-selectin in the regulation of leukocyte attachment to endothelium.
Schleiffenbaum
B
B
Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Spertini
O
O
Tedder
T F
TF
D015153:Blotting, Western; D002448:Cell Adhesion / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000097:blood / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004727:Endothelium / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D019041:L-Selectin; D008214:Lymphocytes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000097:blood / Q000378:metabolism*
D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins; D019041:L-Selectin