Density-dependent induction of TNF-alpha release from human monocytes by immobilized P-selectin. 
P-selectin purified from human platelets, when immobilized on a solid surface, induced monocytes to release tumor necrosis factor-alpha (TNF-alpha).  The induction of TNF-alpha release was dependent on the concentration of P-selectin used for the immobilization, and the maximal stimulation was observed when the plate was coated with 0.3 microgram/ml of P-selectin.  Use of either a higher or a lower concentration of P-selectin for the plate-coating was found to elicit less TNF-alpha release, although the higher concentration of P-selectin caused a stronger adhesion of HL-60 leukemic cells.  The expression of mRNA for TNF-alpha roughly paralleled the TNF-alpha secretion, as assessed by RT-PCR.  These results indicate that monocytes are activated by immobilized P-selectin in a density-dependent manner.