l-selectin is a cell surface receptor on granulocytes, lymphocytes and monocytes that is responsible for the initial attachment of leukocytes to endothelium. The extracellular domain of l-selectin is proteolytically shed from leukocytes following cellular activation in vitro. The shed form of l-selectin (sl-selectin) is functionally active and at high concentrations can inhibit leukocyte attachment to endothelium. Therefore, an ELISA was developed to quantitate the levels of sl-selectin in biological fluids, biopsy specimens and during recombinant protein production. This simple, quantitative sandwich ELISA uses two monoclonal antibodies directed against the extracellular domain of sl-selectin. The assay has a detection range of 5-1300 ng/ml, is precise and sensitive. The ability of this assay to detect sl-selectin in serum, plasma, and culture supernatant fluid was demonstrated and it was used to quantitate circulating sl-selectin in normal and patient sera. Patients with sepsis and HIV infection showed markedly elevated sl-selectin levels in serum. Thus, the ELISA should prove useful both for laboratory purposes as well as in the diagnostic evaluation of patients with inflammatory diseases.
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