Characteristics of the chemotactic activity of heparin cofactor II proteolysis products

The physiological function of the serpin (serine proteinase inhibitor) heparin cofactor II (HCII) is not well understood. A role for HCII as an inhibitor of thrombin in the presence of dermatan sulfate and heparin has been proposed. Neutrophils (PMN) are the major cellular component of acute inflammation. HCII can be proteolytically inactivated by cathepsin G (CG) and elastase (LE), which are released by stimulated PMN. We have recently shown that reaction products of HCII with CG and LE are potent chemotaxins for PMN. Monocytes (monos) appear later in the course of inflammation than do PMN. They differentiate into macrophages in the tissues and participate in healing of damaged tissue and initiating immune responses. We found that the proteolysis products of HCII were chemotactic for monocytes in a fashion similar to their effects on PMN. At 10(-8) to 10(-9) M, the chemotactic activity of HCII proteolysis products was comparable to that of 10(-8) M N-formyl-Met-Leu-Phe (fMLP). The chemotactic activity of HCII-proteinase reaction products is mediated by a different mechanism than that of alpha 1 proteinase inhibitor (alpha 1 PI)-LE complexes or fMLP. Our data suggest that chemotactic activity generated by proteolysis of HCII is not due to the conformational change induced by cleavage of the exposed loop near the reactive site nor by release of the reactive site peptide. We also compared the effects of HCII reaction products and fMLP on expression of Mac-1 and p150,95 adhesive proteins. Mac-1 has been implicated in mono adhesion and chemotaxis and as a potential initiator of coagulation. The surface expression of Mac-1 was not increased above control levels by incubation of leukocytes with HCII digests, even though fMLP did increase surface Mac-1. Proteolysis products of HCII could play a role in the initial influx of PMN into a thrombus, and in the transition from acute to chronic inflammation, or to granulation and healing.