LOW-DENSITY-LIPOPROTEIN RECEPTOR EXPRESSION AND FUNCTION IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Low density lipoprotein receptors (LDLR), capable of internalizing LDL , are expressed in polymorphonuclear neutrophils (PMN). The expression was assessed using anti-LDLR antibody by flow cytometry. The internal ization of LDL was assessed by: (i) quantification of the uptake of la belled LDL with 1,1'-dioctadecyl-3,3,3',3' tetramethyl-indocarboxycyan ine perchlorate (DiI) by flow cytometry; and (ii) the binding of LDL-I -125. I, fresh purified cells, Lineweaver-Burk analysis of LDL binding (LDL-DiI) revealed that the calculated Kd (internalized LDL) for PMN (15.0 x 10(-9) M) is lower than the Kd for monocytes (1.1 x 10(-7) M) and the Kd for lymphocytes (3.2 x 10(-7) M). Scatchard analysis (LDL-I -125) revealed 25 000 binding sites and a Kd of 9.6 x 10(-9) M for PMN . The interaction of LDL with its receptor caused a two-fold fast (pea k at 1 min) and transient increase in the oxidative burst, measured by the formation of 2',7' dicholoflurescein (DCF) by flow cytometry. Thi s effect was not observed in monocytes or lymphocytes, and it was bloc ked by anti-LDLR antibody. The stimulation of LDL was optimal at 10 mu g of protein/ml. LDL was able to suppress DCF formation induced by ph orbol myristate acetate (PMA) and PMA was unable to further stimulate LDL-treated cells, suggesting protein kinase-C (PKC) involvement in LD L effects. Using a PKC assay, LDL was shown to induce a twofold increa se in PKC translocation to the membrane. Thus, LDL increases PMN oxida tive burst through a PKC-dependent pathway.