Fibronectin immobilized to plastic tubes binds soluble Clq with a Kd of 82 ± 2.6 nM. The binding of fibronectin to Clq is relatively insensitive to pH but is sensitive to ionic conditions. Clq covalently bound to Sepharose selectively binds cellular fibronectin produced by a hamster fibroblast cell line. The globular head regions ofClq have no effect on the binding of Clq to fibronectin but the collagenous tails of Clq interfere competitively with a K; of 59 nM. We conclude that fibronectin binds Clq via its collagen-like tail region and thus the process resembles the binding offibronectin to gelatin. This is further emphasized by our observation that gelatin binds to fibronectin immobilized on plastic tubes with a Kd of 131 nM. Because fibronectin stimulates endocytosis in several systems and promotes the clearance of particulate material from the circulation, these results suggest the possibility that fibronectin could function in the clearance of Clqcoated material such as immune complexes or cellular debris.Fibronectins are large glycoproteins that are found at cell surfaces, in extracellular matrices, and in blood plasma (reviewed in refs.
BerneThis work was supported by grants from the "Schweizeriscber Nationalfonds zur Forderung wissenschaftlicher Forschung", the "Kommission zur Forderung der EiweiBforschung an der Universitat Bern", and the "Sandoz-Stiftung zur Forderung der medizinisch-biologischen Forschung".
Five differently isolated and purified human C1q preparations were examined by electron microscopy and analyzed by polyacrylamide gel electrophoresis in 0.1% sodium dodecyl sulfate and 0.5 M urea. The amino acid and carbohydrate composition of C1q purified by the DNA method are reported and compared with results obtained on C1q isolated by other procedures. Electron microscopy showed that all C1q preparations had six peripheral subunits connected by fibrillar strands to a central subunit. The presence of small amounts of dimers was also observed. The physico-chemical properties of the molecule are independent of the purification method used. The five C1q preparations labeled with 125I in presence of lactoperoxidase formed two types of noncovalently linked subunits. In each case the smaller (central) subunit contained over thirty times as much radioactivity as the larger (peripheral) subunit supposed to interact with immune complexes. Reduction and alkylation confirmed for each preparation the presence of three polypeptide chains, the smaller of which contained essentially all radioactivity.
The concentration of IgG, IgA and IgM has been measured in the cervico-vaginal secretions of 8 women with a normal menstrual cycle, 52 pregnant women, 6 post-menopausal women and 12 women with total hysterectomy. No significant difference in immunoglobulin levels was found in the cervico-vaginal secretions of women with a normal cycle as compared to those of post-menopausal or pregnant women. A significant decrease of the IgG/IgA ratio was noticed during ovulation as a consequence of increased IgA secretion. In patients with hysterectomy, the secretions are of vaginal origin only and contain negligible quantities of IgA. Secretory IgA is found essentially in the superior genital tract. IgM is present in trace amounts in all secretions and does not vary considerably. The secretion of immunoglobulins may be under hormonal control: in addition to ovarian hormones, corticosteroids seem also to be involved. The local application of a fluorinated corticosteroid into the vagina has produced a significant decrease of secretory IgA production. The therapeutic possibilities of administering a fluorinated corticosteroid in cases of sterility which are due to the production of anti-spermatozoal antibodies are discussed.
Non-immune activation of the first component of complement (C1) by the heart mitochondrial inner membrane has been investigated. Cardiolipin, the only strong activator of C1 among phospholipids, is present in large amounts in the heart mitochondrial inner membrane. We therefore studied its contribution to C1 activation by mitochondria. The proteins of the mitochondrial inner membrane were found to activate C1 only weakly, in contrast with the phospholipid fraction which induces strong C1 activation. Furthermore, the digestion of mitochondrial inner membranes with proteolytic enzymes did not affect C1 activation. Additional support in favour of cardiolipin being the responsible activator came from competition experiments with mitochondrial creatine kinase (mt-CPK) and adriamycin, known to bind to cardiolipin. Both mt-CPK and adriamycin displaced C1q from the mitochondrial inner membrane. In addition, C1q displaced mt-CPK bound to mitoplasts.
Bovine serum IgG1, colostral IgG1 and serum IgG2 with anti-ferritin activity were digested with pepsin or trypsin. Their fragments were characterized by immunoelectrophoresis, gel electrophoresis and gel filtration; their ferritin-binding ability was determined. The kinetics of proteolysis were established by measuring the appearance of free amino groups. No differences were observed between serum and colostrum IgG1. IgG1 was more susceptible to pepsin, and IgG2 to trypsin. This became evident from both the amount of intact IgG determined by gel electrophoresis, immunoelectrophoresis or gel filtration, and from the kinetics of the appearance of amino groups. A model is presented to explain the size, mobilities and properties of the obtained fragments.
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