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At least 181 records · Page 10Linked to original sources
PubMed1982

Ultrastructure of the first component of human complement: electron microscopy of the crosslinked complex.

Electron micrographs are shown of the first component of human complement (C1) which has been crosslinked with a water-soluble carbodiimide to prevent dissociation into its C1q and C1r2C1s2 subunits. Two projections of the crosslinked molecule are seen in the electron micrographs, which are called "top" and "profile." In both views, the C1q heads are visible. From the top, the C1r2C1s2 tetrameric subunits appears to be located centrally on the C1q and folded to form a compact mass obscuring most of the arms and central bundle. In profile, the tetramer appears to be located in the region of the arms between the C1q heads and the central bundle. Both the heads and the rod-like central bundle appear to be free of C1r2C1s2 in these profile projections. Sometimes it is possible to count more than six domains in the region of the C1q heads, as though a portion of the tetramer had unfolded to protrude among the heads.

Complement C1↗
PubMed1981

Expression of biological effector functions by immunoglobulin G molecules lacking the hinge region.

Several biological effector functions mediated by sites on the Fc region of human IgG1 have been studied in two variant IgG1 kappa monoclonal proteins (Dob and Lec) which contain deletions corresponding to the entire hinge region of the heavy chains. Neither Dob nor Lec protein in aggregated form was able to activate the classical complement pathway, and this was shown to be due to an inability to bind the first component of complement (C1). By rosette inhibition assays, Dob and Lec proteins were shown to have no measurable affinity for Fc receptors on human B cells or neutrophils. Dob and Lec proteins had a much reduced affinity for Fc receptors on the murine macrophage-like cell line P388D1 when compared to normal human IgG1. Furthermore, the hinge-deleted proteins were able to compete with murine IgG2b for P388D1 receptors but not with murine IgG2a. In contrast, the binding of Dob and Lec proteins to protein A from Staphylococcus aureus was entirely normal. The functional consequences of the hinge deletion were parallel to those seen when normal IgG1 was reduced and alkylated. It was concluded that the functional impotency of Dob and Lec proteins was related to the close association between the Fab and Fc regions in these molecules and the limited degree of segmental flexibility permitted in the absence of the hinge region. The data also suggest a major role for the C gamma 2 domain (C is the constant region) in mediating effector functions in normal IgG1.

Animals↗
PubMed1979

C1q: isolation from human serum in high yield by affinity chromatography and development of a highly sensitive hemolytic assay.

C1q, a subcomponent of the first component of complement, has been isolated from human serum in fully hemolytically active form by affinity column chromatography and gel filtration with Bio-Gel A-5M. The affinity column was prepared by covalent coupling of purified human IgG to CNBr-activated Sepharose 4B. Final yields of C1q ranged from 25 to 40% with 650- 890-fold purification based on recovery of hemolytic activity. The preparations were free of contaminating serum proteins as judged by SDS-polyacrylamide gel electrophoretic and immunochemical criteria. The final C1q preparations were also devoid of any demonstrable C1q-inhibitor activity. A C1q-depleted reagent (C1qD) was obtained from the nonabsorbed protein containing fractions of the human IgG-Sepharose 4B affinity column and utilized in conjunction with sensitized sheep erythrocytes (EA) for the detection and quantitation of C1q hemolytic activity. Employing optimal quantities of C1qD in the hemolytic assay mixture, the highly purified C1q preparations contained 0.5 to 1 x 10(13) effective molecules/mg and 0.5 to 1 x 10(12) effective C1q molecules/ml of human serum. This assay would therefore reproducibly detect less than 1 ng of C1q hemolytic activity.

Chromatography, Affinity↗
PubMed1992

Erythromycin inhibits Cl secretion across canine tracheal epithelial cells.

We studied the effect of the macrolide antibiotic erythromycin on bioelectrical properties of canine cultured tracheal epithelium under short-circuit conditions in vitro. Addition of erythromycin to the submucosal but not to the mucosal side dose-dependently decreased short-circuit current (Isc), the maximal decrease from the baseline value and the concentration required to produce a half-maximal effect (IC50) being 5.6 +/- 1.0 microA.cm-2 (mean +/- SE, p less than 0.001) and 18 microM, respectively. In contrast, other antibiotics including ampicillin, cephazolin and tetracycline were without effect. The erythromycin-induced decrease in Isc was not altered by amiloride, but it was abolished by bumetanide, diphenylamine-2-carboxylate2, and substitution of Cl in the bathing medium with gluconate (p less than 0.001, in each case). The effect of erythromycin on epithelial Isc was attenuated by pretreatment of cells with indomethacin but not with AA-861 a lipoxygenase inhibitor. Incubation of cells with erythromycin inhibited the release of prostaglandins E2 and F2 alpha from tracheal epithelial cells. These results indicate that erythromycin may selectively inhibit Cl secretion across airway epithelium through the inhibition of prostaglandin synthesis and suggest that this action possibly reflects its clinical efficacy in the treatment of airway hypersecretion.

Animals↗
PubMed1978

Lysis of C1Q-coated chicken erythrocytes by human lymphoblastoid cell lines.

Human lymphoblastoid cells lysed chicken erythrocytes (E) that carried cell surface bound human C1q. Antibody to E(A) was not required for the C1q-dependent reaction. The effect of C1q was inhibited by Fab'2 anti-C1q and by the serum C1q inhibitor. The action of the lymphoblastoid cells was inhibited by anti-metabolites and by pretreatment of the cells with trypsin which is known to destroy their C1q receptor. Lymphoblastoid cell lysate was inactive. The time course of the C1q-dependent lysis was comparable to that of the antibody-dependent cellular cytotoxic reaction of human K-cells. Lysis of EA by human peripheral lymphocytes was enhanced up to 50% by human C1q.

Animals↗
PubMed1978

C-1 inactivator and cold-promoted activation of factor VII.

When exposed to temperatures between -5 degree and +5 degree C, plasma from pregnant women and from certain blood donors show shortening of the Thrombotest clotting time, kallikrein formation, and activation of blood-clotting factor VII. This phenomenon has been called cold-promoted activation of factor VII (CPA). In this study, it was found that CPA-positive plasma or serum samples which had been exposed to low temepratures showed spontaneous disappearance of C-1-inactivator activity in parallel to the shortening of the Thrombotest clotting time. C-1-inactivator antigen was not affected by storage at 4 degree C. In these CPA-possitive samples the loss of C-1-inactivator activity is caused partially by the formation of kallikrein at this temperature because when kallikrelin was added to C-1 inactivator, the latter was inactive when tested in the esterolytic assay. The formation of Hageman factor fragments may add to further loss. Purified C-1 inactivator effectively inhibited the CPA phenomenon, whereas alpha2-macroglobulin did so only weakly. This finding indicates that during exposure of CPA-positive plasma samples to low temperatures, Hageman factor fragments, which are inhibited only by C-1 inactivator, induce the activation of the kallikrein system and blood clotting factor VII. The reported lowered activity of C-1 inactivator in pregnancy is probably an artifact caused by generation of CPA during storage, since in fresh samples the levels were compeletely normal. Similarly, various subjects classified as belonging to the variant type of HANE (low C-1-inactivator activity with a normal antigen content) were found to have normal C-1-inactivator activity when determinations were made on fresh instead of frozen samples. It is recommended that plasma or serum samples should not be exposed to temperatures between -5degree and +5degree C prior to the determination of C-1-inactivator activity. Moreover, during purification procedures of kallikrein-binding antiproteases such as C-1 inactivator and also alpha2-macroglobulin, the occurrence of CPA should be avoided by the use of CPA-negative plasma as starting material.

Cold Temperature↗