Protein H, an antiphagocytic surface protein in Streptococcus pyogenes. (1/741)

Surface-associated M protein is a major virulence factor in Streptococcus pyogenes which confers bacterial resistance to phagocytosis. However, many S. pyogenes strains also express additional structurally related so-called M-like proteins. The strain studied here is of the clinically important M1 serotype and expresses two structurally related surface proteins, the M1 protein and protein H. Mutants were generated that expressed only one or none of these proteins at the bacterial surface. For survival in human blood either protein H or M1 protein was sufficient, whereas the double mutant was rapidly killed. The protein-binding properties of protein H, M1 protein, and the mutants suggest that bacterial binding of immunoglobulin G and factor H or factor H-like protein 1, which are regulatory proteins in the complement system, contribute to the antiphagocytic property.  (+info)

Multicenter trial of the quantitative BTA TRAK assay in the detection of bladder cancer. (2/741)

BACKGROUND: Human complement factor H-related protein (hCFHrp) is produced by several bladder cancer cell lines and may be useful as a cancer marker. The aim of this study was to compare urinary hCFHrp and cytology for the detection of bladder cancer found by cystoscopy in patients with suggestive signs, symptoms, or preliminary test results. METHODS: The BTA TRAK assay, a quantitative enzyme immunoassay for the bladder tumor-associated antigen in urine, was compared with exfoliative cytology in 220 patients (155 men, 65 women; mean age, 64.2 years) presenting with signs, symptoms, or preliminary diagnostic results suggestive of this disease. Cystoscopy was the standard of detection. RESULTS: In the 100 patients found to have bladder cancer, the overall sensitivities of the BTA TRAK assay (at a previously determined decision threshold of 14 kilounits/L) and cytology were 66% (66 of 100) and 33% (33 of 100), respectively (P <0.001). The BTA TRAK assay proved to be statistically more sensitive than cytology for tumor grades I and II and for stage Ta and T1 tumors. In contrast, the overall specificity of the BTA TRAK assay in the 120 patients without cystoscopically confirmed bladder cancer was 69% (83 of 120) and that of cytology was 99% (119 of 120; P <0.001). The specificity of the BTA TRAK assay was higher in patients without benign or malignant genitourinary disease other than bladder cancer (76%; n = 89) than in patients with these conditions. When the BTA TRAK assay and cytology were used together such that a positive result in either test was scored as positive and the results compared with those of the BTA TRAK assay alone, increases in overall sensitivity and equivalent specificity were observed. CONCLUSION: Because of its relatively high sensitivity, the BTA TRAK assay could complement cytology as an adjunct to cystoscopy in the diagnosis and follow-up of most patients with bladder cancer.  (+info)

In vitro analysis of complement-dependent HIV-1 cell infection using a model system. (3/741)

Previous studies based on the use of human serum as a source of C have provided evidence for the C-dependent enhancement of cell infection by HIV-1. The present study was undertaken to distinguish C from other serum factors and to identify the proteins and the mechanisms involved in C-dependent cell infection by HIV-1. The classical C activation pathway was reconstituted from the proteins C1q, C1r, C1s, C4, C2, C3, factor H, and factor I; each were purified to homogeneity. A mixture of these proteins at physiological concentrations was shown to reproduce the ability of normal human serum to enhance the infection of MT2 cells by HIV-1 at low doses of virus. This enhancing effect was abolished when heat-inactivated serum and C2- or C3-depleted serum were used, and was restored upon addition of the corresponding purified proteins. A mixture of two synthetic peptides corresponding to positions 10-15 and 90-97 of human C receptor type 2 (CD21) as well as soluble CD4 both inhibited the C-dependent infection process. These data provide unambiguous evidence that HIV-1 triggers a direct activation of the classical C pathway in vitro and thereby facilitates the infection of MT2 cells at low doses of virus. These findings are consistent with a mechanism involving increased interaction between the virus opsonized by C3b-derived fragment(s) and the CD21 cell receptors and subsequent virus entry through CD4 receptors.  (+info)

Disruption of disulfide bonds is responsible for impaired secretion in human complement factor H deficiency. (4/741)

Factor H, a secretory glycoprotein composed of 20 short consensus repeat modules, is an inhibitor of the complement system. Previous studies of inherited factor H deficiency revealed single amino acid substitutions at conserved cysteine residues, on one allele arginine for cysteine 518 (C518R) and on the other tyrosine for cysteine 941 (C941Y) (Ault, B. H., Schmidt, B. Z., Fowler, N. L., Kashtan, C. E., Ahmed, A. E., Vogt, B. A., and Colten, H. R. (1997) J. Biol. Chem. 272, 25168-25175). To ascertain if the phenotype, impaired secretion of factor H, is due to the C518R substitution or the C941Y substitution and to ascertain the mechanism by which secretion is impaired, we studied COS-1 and HepG2 cells transfected with wild type and several mutant factor H molecules. The results showed markedly impaired secretion of both C518R and C941Y factor H as well as that of factor H molecules bearing alanine or arginine substitutions at the Cys518-Cys546 disulfide bond (C518A, C546A, C546R, C518A-C546A). In each case, mutant factor H was retained in the endoplasmic reticulum and degraded relatively slowly as compared with most other mutant secretory and membrane proteins that are retained in the endoplasmic reticulum. These data indicate that impaired secretion of the naturally occurring C518R and C941Y mutant factor H proteins is due to disruption of framework-specific disulfide bonds in factor H short consensus repeat modules.  (+info)

Hypocomplementemia discloses genetic predisposition to hemolytic uremic syndrome and thrombotic thrombocytopenic purpura: role of factor H abnormalities. Italian Registry of Familial and Recurrent Hemolytic Uremic Syndrome/Thrombotic Thrombocytopenic Purpura. (5/741)

Familial hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) carry a very poor outcome and have been reported in association with decreased serum levels of the third complement component (C3). Uncontrolled consumption in the microcirculation, possibly related to genetically determined deficiency in factor H--a modulator of the alternative pathway of complement activation--may account for decreased C3 serum levels even during disease remission and may predispose to intravascular thrombosis. In a case-control study by multivariate analysis, we correlated putative predisposing conditions, including low C3 serum levels, with history of disease in 15 cases reporting one or more episodes of familial HUS and TTP, in 25 age- and gender-matched healthy controls and in 63 case-relatives and 56 control-relatives, respectively. The relationship between history of disease, low C3, and factor H abnormalities was investigated in all affected families and in 17 controls. Seventy-three percent of cases compared with 16% of controls (P < 0.001), and 24% of case-relatives compared with 5% of control-relatives (P = 0.005) had decreased C3 serum levels. At multivariate analysis, C3 serum level was the only parameter associated with the disease within affected families (P = 0.02) and in the overall study population (P = 0.01). Thus, subjects with decreased C3 serum levels had a relative risk of HUS or TTP of 16.56 (95% confidence interval [CI], 1.66 to 162.39) within families and of 27.77 (95% CI, 2.44 to 314.19) in the overall population, compared to subjects with normal serum levels. Factor H abnormalities were found in four of the cases, compared with three of the healthy family members (P = 0.02) and none of the controls (P = 0.04) and, within families, factor H abnormalities were correlated with C3 reduction (P < 0.05). Reduced C3 clusters in familial HUS and TTP is likely related to a genetically determined deficiency in factor H and may predispose to the disease. Its demonstration may help identify subjects at risk in affected families.  (+info)

Familial relapsing haemolytic uraemic syndrome and complement factor H deficiency. (6/741)

BACKGROUND: In a recent study of three families we have found that inherited haemolytic uraemic syndrome (HUS) maps to a region of chromosome 1q containing the gene for complement factor H. In one of these families and also in a case of sporadic D-HUS, we have identified mutations in the factor H gene. A further family with inherited HUS has therefore been investigated. METHODS: DNA extracted from the family members and DNA extracted from archival post-mortem material from a deceased family member, was studied. Review of renal biopsies and study of complement components was also undertaken. RESULTS: This family demonstrates an inherited deficiency of complement factor H. Non-diarrhoeal HUS has affected at least two family members with half normal levels of factor H. CONCLUSION: These findings represent further evidence of the association between factor H dysfunction and HUS.  (+info)

Identification of human complement Factor H as a ligand for L-selectin. (7/741)

The selectin family of adhesion molecules (E-, P- and L-selectins) is involved in leukocyte recruitment to sites of inflammation and tissue damage. Recently it has been shown that L-selectin is involved not only in leukocyte tethering and rolling, but also plays an important role in leukocyte activation. For example, glycosylation-dependent cell-adhesion molecule 1 (GlyCAM-1), a known ligand for L-selectin, has been shown to enhance beta2-integrin function. GlyCAM-1 is a secreted protein and is present in mouse serum at a concentration of approx. 1.5 microg/ml. There is no obvious GlyCAM-1 homologue in man and, to date, L-selectin ligand(s) from human serum have not been characterized. Therefore we have used L-selectin affinity chromatography, followed by ion-exchange chromatography, to isolate specific ligand(s) for L-selectin. Using this procedure, we have isolated three major glycoproteins of apparent molecular masses 170 kDa, 70kDa and 50 kDa. The 170 kDa protein band was digested with trypsin and peptides were analysed by delayed extraction matrix-assisted laser desorption ionization MS and protein database searching. The 170 kDa protein was identified as the human complement protein Factor H. Human Factor H, isolated by a different method, was shown to bind specifically to L-selectin in the presence of CaCl2, and binding was inhibited by anti-L-selectin antibodies, fucoidan and lipopolysaccharide. Only a part of the purified Factor H preparation bound to immobilized L-selectin. The interaction of Factor H with leukocyte L-selectin was shown to induce the secretion of tumour necrosis factor-alpha (TNF-alpha). Pretreatment of Factor H with sialidase reduced both the binding of L-selectin to Factor H and the Factor H-induced L-selectin-mediated TNF-alpha secretion by leukocytes. Taken together, these results demonstrate that a post-translationally modified form of human plasma Factor H is a potential physiological ligand for L-selectin.  (+info)

Resistance to both complement activation and phagocytosis in type 3 pneumococci is mediated by the binding of complement regulatory protein factor H. (8/741)

To study the role of surface-associated proteins in the virulence of Streptococcus pneumoniae, we used two serotype 3 strains, ATCC 6303 and WU2, and two PspA-negative mutants of WU2, an encapsulated one, JY1123 (Caps(+)/PspA(-)), and an unencapsulated one, DW3.8 (Caps(-)/PspA(-)). ATCC 6303 and WU2 were highly virulent in mice, while the virulence of JY1123 was slightly decreased (50% lethal doses [LD(50)s], 24, 6, and 147 CFU/mouse, respectively); DW3.8 was avirulent (LD(50), 2 x 10(8) CFU). In vitro, ATCC 6303, WU2, and JY1123 (Caps(+)/PspA(-)) strongly resisted complement activation and complement-dependent opsonophagocytosis, whereas DW3.8 (Caps(-)/PspA(-)) was easily phagocytized in fresh serum. Trypsin treatment of ATCC 6303, WU2, and JY1123 (Caps(+)/PspA(-)) resulted in enhanced complement activation and complement-dependent opsonophagocytosis. Trypsin had no deleterious effect on the polysaccharide capsule. In addition, trypsin pretreatment of ATCC 6303 strongly reduced virulence upon intraperitoneal challenge in mice. This indicated that surface proteins play a role in the resistance to complement activation and opsonophagocytosis and contribute to the virulence of type 3 pneumococci. In subsequent experiments, we could show that the modulation of complement activation was associated with surface components that bind complement regulator factor H; binding is trypsin sensitive and independent of prior complement activation. Immunoblotting of cell wall proteins of the virulent strain ATCC 6303 with anti-human factor H antibody revealed three factor H-binding proteins of 88, 150, and 196 kDa. Immunogold electron microscopy showed a close association of factor H-binding components with the outer surface of the cell wall. The role of these factor H-binding surface proteins in the virulence of pneumococci is interesting and warrants further investigation.  (+info)