Complement C5a (desArg) generation in serum exposed to damaged aortic endothelium

Vascular endothelial growth factor attenuates trauma-induced injury in rats

Endothelial dysfunction and loss of nitric oxide (NO) is an integral part of the initiation and maintenance of the inflammatory process such as that occurring in traumatic shock, and is considered responsible for much of the trauma induced microvascular injury. We investigated the effects of a vascular endothelial growth factor (VEGF) in a rat model of traumatic shock. Pentobarbital-anaesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension and a 93% mortality rate with a mean survival time of 108+/-10 min in 14 rats. Accompanying these effects was a significant degree of endothelial dysfunction and a markedly elevated intestinal myeloperoxidase (MPO) activity. Treatment with 125 microg kg(-1) VEGF administered intravenously 18 h pre-trauma, increased survival rate to 67% (P<0.01), and prolonged survival time to 252+/-24 min in 12 rats (P<0.01). VEGF also significantly preserved the endothelium-dependent relaxation to ACh indicating a preservation of endothelium-derived NO. Our results indicate that endothelial dysfunction with its accompanying loss of NO plays an important role in tissue injury associated with trauma, and that preservation of NO is beneficial in traumatic shock. The mechanisms of the protective effect of VEGF in trauma involves preservation of eNOS function and diminished neutrophil accumulation resulting in reduced neutrophil-mediated tissue injury. British Journal of Pharmacology (2000) 129, 71 - 76

Complement activation by pulsed tunable dye laser in normal skin and hemangioma

Pulsed tunable dye laser (577 nm) (PTDL) therapy induces hemoglobin coagulation and tissue necrosis, which is mainly limited to blood vessels. To define whether this treatment activates complement in normal skin and senile hemangioma, we analyzed complement deposition in blood vessels by immunofluorescence. C3 fragments, C8, and C9 were detected with specific polyclonal antibodies. The membrane attack complex of complement (MAC) was demonstrated with a monoclonal antibody which reacts only with a neoantigen of MAC. Amplification of C3 deposition by the alternative pathway was determined on cryostat sections by indirect immunofluorescence with use of C4 deficient guinea pig (GP) serum. Normal skin and hemangiomas from three individuals were studied. In PTLD-irradiated normal skin, the main findings were as follows: 1) C3 fragments, C8, C9, and MAC were deposited in vessel walls; 2) these deposits were not due to denaturation of the proteins since they became apparent only 7 min after irradiation, contrary to immediate deposition of transferrin at the sites of erythrocyte coagulates; 3) the C3 deposits were shown to amplify complement activation by the alternative pathway, a reaction which was specific since tissue necrosis itself did not lead to such amplification; 4) these reactions preceded the local accumulation of polymorphonuclear leucocytes. Tissue necrosis was more pronounced in the hemangiomas. The larger angiomatous vessels in the center of the necrosis did not fix complement significantly. By contrast, complement deposition in the vessels situated at the periphery was similar to that observed in normal skin with one exception: C8, C9, and MAC were detected in some blood vessels immediately after laser treatment, a finding consistent with assembly of the MAC occurring directly without the formation of a C5 convertase. These results indicate that complement is activated in PTDL-induced vascular necrosis, and might be responsible for the ensuing inflammatory response.

Complement receptors and regulatory proteins in human atherosclerotic lesions

Complement activation in human atherosclerotic lesions is indicated by the presence of C5b-9 terminal complexes. By using monoclonal antibodies to the complement C3b receptor (CR1) and the iC3b receptor (CR3), it was observed that approximately 20% of the cells in complicated human carotid lesions express CR1 and CR3 antigens. One to five percent of complement receptor-positive cells stained for smooth muscle cell-specific myosin, and the remainder were determined to be predominantly macrophages, based on their reactivity to anti-LeuM3 (CD14) monoclonal antibody. No C3dg receptor (CR2)-positive cells were observed in any of the eight lesions examined. The complement regulatory glycoprotein decay accelerating factor (DAF) was widely distributed extracellularly, in addition to being present on 20% to 60% of the total cell population. Factor H, a plasma protein that regulates alternative pathway C3 convertase formation, was observed extracellularly in 70% of the lesions examined. C1 inhibitor was present in a few plaque specimens, was relatively sparse, and appeared largely cell associated. Terminal C5b-9 complement complexes were pervasive in all lesions. Both the complement regulatory proteins and the activation products were limited to the area of lesion involvement and were absent from normal arterial wall. The results demonstrate that molecules involved in complement regulation and complement ligand binding are present in atherosclerotic lesions, where they may function to modulate the activities of complement.

Decay-accelerating factor is expressed on vascular smooth muscle cells in human atherosclerotic lesions

Decay-accelerating factor (DAF) is a constitutively expressed plasma membrane glycoprotein on blood cells and endothelium that inhibits cell surface C3/C5 convertase formation, thus inhibiting complement activation and protecting cells from lysis by the terminal complement components. Using monoclonal anti-DAF antibodies in conjunction with anti-smooth muscle cell (SMC)-specific myosin antibodies, it was found by immunohistochemistry that vascular SMC in advanced human carotid atherosclerotic lesions express DAF antigen. The percentage of DAF-positive SMC ranged from 20 to 60% between different patient samples and SMC DAF expression was limited to SMC in the lesion proper. Normal arterial wall SMC exhibited no DAF-specific immunostaining. Essentially 100% of passaged cultured vascular SMC derived from normal human uterine artery, or from umbilical vein, expressed DAF as assessed by immunocytochemistry. A 68-kD band was observed on SDS-PAGE autoradiograms of DAF-immunoprecipitated radiolabeled cultured SMC extracts. Sensitization of rabbit erythrocytes with DAF-containing SMC extracts conferred protection against complement-mediated hemolysis in normal human serum and the protective effect could be reversed by treatment with anti-DAF antibodies. We conclude that DAF is induced on vascular SMC during atherogenesis and in culture.

The complement system in atherosclerosis

Complement is a term referring to a collection of plasma proteins, specific cellular receptors and cell surface regulatory molecules. Activation of the complement system to completion results in the formation of C5b-9 terminal complexes. These complexes have been observed in human atherosclerotic lesions by immunohistochemistry. Although the structure(s) which activate complement in lesions have not been defined, cholesterol and oxysterols exhibit this property in vitro. Endothelial cell damage leads to complement activation and endothelial cells overlying atherosclerotic lesions have been observed to contain C3 and C5b-9 antigens. Cardiac myocytes stain for complement proteins (C3, C4 and C5b-9) following myocardial infarction. Infarct size and extent of inflammatory cell infiltrates are diminished by decomplementation prior to experimentally-induced myocardial ischemia. Following myocardial infarction and ulceration of atherosclerotic lesions in human patients there is an increase in circulating complement activation products and a decrease in the level of native C1 through C4 proteins. Thus, it appears that complement plays a role in atherogenesis and its sequelae. Little is known however, about the pathophysiological effects complement activation products exert on lesion development, for example through modulation of macrophage functions, or how complement activation is regulated in lesions. Implications for complement in atherogenesis are discussed.