Proteolytic activation transforms heparin cofactor II into a host defense molecule.

The abundant serine proteinase inhibitor heparin cofactor II (HCII) has been proposed to inhibit extravascular thrombin. However, the exact physiological role of this plasma protein remains enigmatic. In this study, we demonstrate a previously unknown role for HCII in host defense. Proteolytic cleavage of the molecule induced a conformational change, thereby inducing endotoxin-binding and antimicrobial properties. Analyses employing representative peptide epitopes mapped these effects to helices A and D. Mice deficient in HCII showed increased susceptibility to invasive infection by Pseudomonas aeruginosa, along with a significantly increased cytokine response. Correspondingly, decreased levels of HCII were observed in wild-type animals challenged with bacteria or endotoxin. In humans, proteolytically cleaved HCII forms were detected during wounding and in association with bacteria. Thus, the protease-induced uncovering of cryptic epitopes in HCII, which transforms the molecule into a host defense factor, represents a previously unknown regulatory mechanism in HCII biology and innate immunity.

[Heparin cofactor II (HCII) activity and antigen assay and their significance in thrombotic diseases].

OBJECTIVE: To study the plasma HCII activity and antigen level variations and their relationship with arterial and deep venous thrombotic diseases. METHODS: Seventy-five patients with brain infarction (BI), 50 myocardial infarction (MI), 36 deep venous thromboembolic disease (DVT) and 50 healthy controls were entered in this study. Plasma HCII activity was measured with chromogenic substrate method and the HCII antigen level by Western blotting assay. Plasma antithrombin (AT) activity was detected for the HCII deficiency individuals with DVT using chromogenic substrate method. RESULTS: There was no significant difference in the mean plasma HCII activity and antigen levels between BI group [(99.97 +/- 21.14)% and 0.96 +/- 0.24], MI group [(98.18 +/- 29.35)% and 0.95 +/- 0.20] and healthy controls [(96.80 +/- 20.11)% and 0.93 +/- 0.19]. The plasma HCII activity and antigen concentrations in patients with DVT [(89.57 +/- 17.12)% and 0.87 +/- 10.18] tended to be decreased as compared with healthy controls, but they were not significant. No significant difference was found for the prevalence of HCII deficiency between patient groups and control group. The HCII deficiency individuals with DVT had normal AT activity and fibrinogen concentration. CONCLUSIONS: Plasma HCII deficiency may not be the risk factor for arterial thrombosis in the Han population of Hunan Chinese. It is needed to further confirm if decreased plasma HCII is correlated with venous thrombosis.

[Dynamic changes and localization of plasma heparin cofactor II before and after delivery in hypertensive pregnancy].

OBJECTIVE: To explore the physiological significance of the anticoagulation effect of heparin cofactor II (HCII) in vivo and investigate the pathogenesis of the development of thrombosis in hypertensive pregnancy. METHODS: 1. Plasma level of HCII activity was measured by chromogenic assay in 18 healthy adults, 18 normal pregnant women and 29 hypertensive pregnant women before and after delivery. 2. Plasma level of HCII antigen was measured by Western blot in 29 hypertensive pregnant women before and after delivery. 3. The distribution of HCII in the placenta was determined by immunofluorescent method. RESULTS: The plasma HCII activity and antigen content in hypertensive pregnancy decreased significantly before delivery. They correlated with the severity of hypertensive pregnancy, and restored to normal after delivery. No HCII was found in normal and pathological placenta. CONCLUSION: 1. Plasma HCII activity decreased during pregnancy in hypertensive pregnancy. 2. The placenta is not the target of HCII. 3. Dynamic determination of plasma HCII level can reflect the severity of hypertensive pregnancy and be used as one of prognostic indices.

Heparin cofactor II in diabetic patients.

Levels of heparin cofactor II (HCII) activity and antigen and electrophoretic pattern were studied both in normal subjects and in type I diabetic patients with high and normal levels of glycosylated haemoglobin. There was a significant reduction in HCII activity (83 +/- 7%) in patients with high levels of glycosylated haemoglobin compared with controls (95 +/- 17%; P < 0.001). However, plasma HCII antigen levels were not decreased in these patients.

Purification of heparin cofactor II from human plasma.

Heparin cofactor II (HCII) is an inhibitor of thrombin in human plasma whose activity is enhanced by heparin and dermatan sulphate. HCII was purified to homogeneity from normal human plasma with an overall yield of 7.5%. After treatment with barium chloride, precipitation with 50% saturated ammonium sulphate and dialysis of the resuspended precipitate against 0.02 M Tris-HCl (pH 7.4), the sample was chromatographed on a heparin-Sepharose CL 6B affinity column, DEAE-Sepharose CL 6B ion-exchange gel and an AcA 34 gel permeation column. For the final steps, a high-performance liquid chromatographic system was used which included ion-exchange chromatography on a Mono-Q column and gel permeation using a Superose column. The purified protein was homogeneous by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The specific activity of purified HCII was 12.2 U/mg. The HCII activity was evaluated as antithrombin dermatan sulphate cofactor activity. A specific antiserum against HCII was raised in the rabbit.