Complement Receptor Type 1 (CR1, CD35) Is a Receptor for C1q

AbstractMolecular definition of the cellular receptor for the collagen domain of C1q has been elusive. We now report that C1q binds specifically to human CR1 (CD35), the leukocyte C3b/C4b receptor, and the receptor on erythrocytes for opsonized immune complexes. Biotinylated or radioiodinated C1q (*C1q) bound specifically to transfected K562 cells expressing cell surface CR1 and to immobilized recombinant soluble CR1 (rsCR1). *C1q binding to rsCR1 was completely inhibited by unlabeled C1q and the collagen domain of C1q and was partially inhibited by C3b dimers. Kinetic analysis in physiologic saline of the interaction of unlabeled C1q with immobilized rsCR1 using surface plasmon resonance yielded an apparent equilibrium dissociation constant (Keq2) of 3.9 nM. Thus, CR1 is a cellular C1q receptor that recognizes all three complement opsonins, namely, C1q, C3b, and C4b

Complement Receptor 1/Cd35 Is a Receptor for Mannan-Binding Lectin

Mannan-binding lectin (MBL), a member of the collectin family, is known to have opsonic function, although identification of its cellular receptor has been elusive. Complement C1q, which is homologous to MBL, binds to complement receptor 1 (CR1/CD35), and thus we investigated whether CR1 also functions as the MBL receptor. Radioiodinated MBL bound to recombinant soluble CR1 (sCR1) that had been immobilized on plastic with an apparent equilibrium dissociation constant of 5 nM. N-acetyl-d-glucosamine did not inhibit sCR1–MBL binding, indicating that the carbohydrate binding site of MBL is not involved in binding CR1. C1q inhibited MBL binding to immobilized sCR1, suggesting that MBL and C1q might bind to the same or adjacent sites on CR1. MBL binding to polymorphonuclear leukocytes (PMNs) was associated positively with changes in CR1 expression induced by phorbol myristate acetate. Finally, CR1 mediated the adhesion of human erythrocytes to immobilized MBL and functioned as a phagocytic receptor on PMNs for MBL–immunoglobulin G opsonized bacteria. Thus, MBL binds to both recombinant sCR1 and cellular CR1, which supports the role of CR1 as a cellular receptor for the collectin MBL

Measurement of MMP-9 and -12 degraded elastin (ELM) provides unique information on lung tissue degradation

BACKGROUND: Elastin is an essential component of selected connective tissues that provides a unique physiological elasticity. Elastin may be considered a signature protein of lungs where matrix metalloprotease (MMP) -9-and -12, may be considered the signature proteases of the macrophages, which in part are responsible for tissue damage during disease progression. Thus, we hypothesized that a MMP-9/-12 generated fragment of elastin may be a relevant biochemical maker for lung diseases. METHODS: Elastin fragments were identified by mass-spectrometry and one sequence, generated by MMP-9 and -12 (ELN-441), was selected for monoclonal antibody generation and used in the development of an ELISA. Soluble and insoluble elastin from lung was cleaved in vitro and the time-dependent release of fragments was assessed in the ELN-441 assay. The release of ELN-441 in human serum from patients with chronic obstructive pulmonary disease (COPD) (n = 10) and idiopathic pulmonary fibrosis (IPF) (n = 29) were compared to healthy matched controls (n = 11). RESULTS: The sequence ELN-441 was exclusively generated by MMP-9 and -12 and was time-dependently released from soluble lung elastin. ELN-441 levels were 287% higher in patients diagnosed with COPD (p < 0.001) and 124% higher in IPF patients (p < 0.0001) compared with controls. ELN-441 had better diagnostic value in COPD patients (AUC 97%, p = 0.001) than in IPF patients (AUC 90%, p = 0.0001). The odds ratios for differentiating controls from COPD or IPF were 24 [2.06–280] for COPD and 50 [2.64–934] for IPF. CONCLUSIONS: MMP-9 and -12 time-dependently released the ELN-441 epitope from elastin. This fragment was elevated in serum from patients with the lung diseases IPF and COPD, however these data needs to be validated in larger clinical settings

A human neutrophil-dependent pathway for generation of angiotensin II: Purification and physicochemical characterization of the plasma protein substrate.

A B S T R A C T A human neutrophil lysosomal protease interacts at physiologic pH with a 62,000-67,000-mol wt plasma protein substrate to generate a vasoactive, smooth muscle-contracting &quot;neutral&quot; peptide. The peptide product of this system, previously designated the &quot;neutral&quot; peptide-generating pathway, was generated from purified components and purified by Bio-Gel P2 gel filtration and reverse-phase high performance liquid chromatography with a 50-60% yield of starting activity. The purified peptide had an amino acid composition of Asx, Pro, Val, Ile, Tyr, Phe, His, Arg, a composition identical to that of angiotensin II. The peptide and synthetic angiotensin II each filtered at 48-52% bed volume on Bio-Gel P2, had an isoelectric point of pH 7.8-8.1 at 4°C, migrated 3 cm toward the cathode during pH 6.4 low-voltage paper electrophoresis, and had a retention time of 44.8 min during reverse-phase high-performance liquid chromatography. In addition, the functional activity of the peptide at each purification step correlated with angiotensin II content determined by specific radioimmunoassay. The amino acid sequence of 25 nmol of the peptide was Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, the same covalent structure as that ofangiotensin II. Therefore, unde