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At least 577 records · Page 32Linked to original sources
PubMed1979

Antibody-independent neutralization of vesicular stomatitis virus by human complement. II. Formation of VSV-lipoprotein complexes in human serum and complement-dependent viral lysis.

Vesicular stomatitis virus (VSV) is efficiently neutralized by normal, nonimmune human serum without the participation of antibody. Neutralization is complement- (C) dependent and requires the early-acting components of the classical pathway, C1, C4, C2, and C3, but not later-acting C components. In further studies, normal human serum was found to markedly increase the density of a variable but significant proportion of virus-associated RNA and to markedly decrease the density of the remainder of virus-associated RNA. The RNA of increased density was found to be dense ribonucleocapsid cores released from VSV by C-dependent viral lysis mediated through the classical pathway. The released ribonucleocapsid cores found at the bottom of sucrose density gradient after incubation of VSV with human serum were resistant to degradation by proteolytic enzymes. The VSV-derived RNA found floating on the tops of sucrose density gradients performed on serum-treated VSV was infectious virus. The decreased density was due to binding of VSV to human serum lipoproteins (LP), primarily very low density lipoproteins (VLDL). Binding of VLDL to VSV required the presence of the viral envelope and the external glycoprotein, G. Despite the binding of LP to VSV, LP did not neutralize VSV, and LP-depleted sera were fully active in neutralizing VSV. Thus, LP do not represent an accessory factor for the C-dependent neutralization of VSV.

Antibodies, Viral↗
PubMed1978

Attempts to evaluate the role of the third complement component (C3) and complement receptor lymphocytes (CRL"+") in the induction of the humoral immune response.

It has been shown that spleen and bone marrow complement receptor lymphocytes (CRL"+") are responsible for T-dependent anti-SRBC response. This has been shown by comparison of the T-dependent anti-SRBC and T-independent anti-SIII response in irradiated mice repopulated with normal or CRL depleted spleen cell populations. Unseparated spleen cells obtained from animals immunized 48 h before with SRBC, and CRL depleted cell population from animals receiving T-independent antigens (levan, SIII) were shown to be predominantly stimulated when uptake of isotope labelled leucine or tymidine was studied. It was also shown that triggering of enhanced antibody production by T cell derived signal generated during GvH reaction is C3 dependent.

Animals↗
PubMed1979

Isolation of late complement components by affinity chromatography. II. Purification of the human complement component C6.

We developed a new procedure for the rapid and gentle isolation of the human complement component C6 comparable to that described previously for C9. The procedure is based on affinity chromatography. As a first step, C6 is immunoabsorbed on insolubilized anti-C6 antibodies. These antibodies were derived from C6-defective rabbits (Freiburg strain). C6 was eluted with 3 M thiocyanate, pH 7.2, with a recovery of 15--23% of its hemolytic activity and a more than 270--fold purification. Impurities were removed in a second step by an "anti-impurity" column. The final product yielded a 12% recovery of the hemolytic activity and the purification factor was higher than 1300. The final product was homogeneous in SDS polyacrylamide and immunoelectrophoresis.

Animals↗
PubMed1979

The complement fixation test and African trypanosomiasis. II. The complement fixation test as an aid for assessing therapy.

Complement-fixing antibody titres decline after successful treatment of trypanosoma infected cattle during a fixed period. For investigating the practicability of the resulting double test procedure in the field, cattle under controlled drug regimes were tested at treatment and again 3 weeks later. Alternatively, the results from groups of treated and untreated animals from the same area were compared. Both serological and parasitological test results indicated an insuffieicnt effectiveness of therapy in the area under investibation.

Animals↗
PubMed1983

Complement-mediated killing of myeloma tumour cells: differences in susceptibility to lysis by antibodies and complement are independent of antigen expression and antibody binding.

The susceptibility to lysis by antibodies (Ab) and complement (C) of several murine myeloma tumour sublines was studied. Significant differences in the degree of C-mediated lysis were observed and found to be independent of the expression of antigens on the cell surface and their accessibility to react with Ab. Several experiments correlate the presence and amount of a 160 kilo dalton cell-surface glycoprotein (gp160) and the diminished susceptibility to C attack observed with some of these tumour sublines. Different sources of Ab and C were tested and similar results were obtained, although the effect was most apparent when mouse Ab and rabbit C were used in the cytotoxicity assays. These results suggest that gp160, when present in large amounts on the cell surface, could be interfering with the generation of the C-induced membrane lesions.

Animals↗
PubMed1984

Purification of a lamprey complement protein homologous to the third component of the mammalian complement system.

A lamprey protein homologous to the third component of mammalian complement was isolated from lamprey plasma and was tentatively designated lamprey C3. Lamprey C3 is a major protein in lamprey serum with electrophoretic mobility of beta-globulin and with m.w. of 190,000. It consists of three polypeptide chains (84,000-alpha, 74,000-beta, and 32,000-gamma chains) linked by disulfide bonds. The protein retains a unique internal thiolester bond on the alpha-chain that is cleaved on methylamine treatment or on limited proteolysis with trypsin. Lamprey C3 by itself could not bind to zymosan or rabbit red cells, but it could covalently bind to these substances when activated by other factors present in lamprey serum. The binding of lamprey C3 to activating surfaces is mediated by covalent bonds and is accompanied by limited proteolysis of the alpha-chain. A fragment with an m.w. of 35,000 containing the internal thiolester site was isolated from methylamine-treated lamprey C3 bound to activated thiol-Sepharose by extensive tryptic digestion followed by dithiothreitol treatment. Lamprey C3 functions as the essential factor in phagocytosis of rabbit red cells by lamprey phagocytes. However, it is not involved in naturally occurring hemolytic activity in lamprey serum.

Animals↗
PubMed1985

Monoclonal antibodies against complement 3 neoantigens for detection of immune complexes and complement activation. Relationship between immune complex levels, state of C3, and numbers of receptors for C3b.

C3-bearing immune complexes and C3 activation products were detected by using two monoclonal antibodies, one specific for a neoantigenic determinant on C3c and the other for C3d. To quantitate immune complexes, the anti-C3c or anti-C3d antibodies were fixed to microtiter plates and reacted with test plasma. The binding of C3-bearing immune complexes in this plasma was then measured with radioisotope- or enzyme-labeled anti-human IgG. To test for C3 breakdown products, solid-phase monoclonal antibody to the C3d neoantigen was reacted with EDTA-plasma samples, and fixed iC3b or C3d was measured with a polyclonal anti-C3 antibody. Patients with autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and Sjogren's syndrome, and paracoccidioidomycosis were found to contain immune complexes bearing C3b/iC3b or C3d. In most conditions, there were more C3d-containing immune complexes than C3b/iC3b. Although CR1 (C3b receptors) rapidly converted immune complex-bound iC3b to C3dg/C3d and lupus patients had reduced CR1, no correlation between the state of C3 on circulating immune complexes or levels of immune complexes and CR1 numbers was seen. However, levels of C3-fixing ICs correlated with levels of C3 activation products. This assay system with monoclonal antibodies to neoantigens expressed on activated, but not native, C3 provides sensitive and specific means for detecting and classifying C3-fixing immune complexes and for assessing C3 activation.

Antibodies, Monoclonal↗
PubMed1980

The terminal membrane C5b-9 complex of human complement. Evidence for the existence of multiple protease-resistant polypeptides that form the trans-membrane complement channel.

C5b-9(m) complexes were incorporated into lecithin liposomes and subjected to proteolysis in the presence of DTT to remove the externally oriented annulus. Liposomes were recovered that selectively carried the membrane-bound, thin-walled cylindrical portion of the C5b-9(m) complex. The presence of DTT during proteolysis enhanced peptide bond cleavage in the C5b-9(m) complex. All C5-C9 components were degraded to lower m.w. fragments. A protease-resistant, but hydrophilic 85 to 86,000-dalton polypeptide derivative of C5, possibly representing the C5 beta-chain, was recovered in the fluid phase. This component is not intimately associated with the target lipid bilayer. Immunochemical analyses yielded evidence for the existence of minor C5-C9 antigenic determinants on the membrane-bound C5b-9(m) residue. SDS polyacrylamide gel electrophoreses of liposomes carrying the C5b-9(m) residues revealed the persistence of at least six major polypeptides of approximately m.w. 50,000, 45,000, 40,000, 38,000, 20,000, and 16,000. The data are interpreted to indicate that multiple protease-resistant polypeptide chains derived from several terminal C components participate in formation of the trans-membrane C channel.

Antigens↗
PubMed1989

Human complement factor H: an additional gene product of 43 kDa isolated from human plasma shows cofactor activity for the cleavage of the third component of complement.

In addition to the 150-kDa factor H protein, we have previously described a 43-kDa factor H molecule in human plasma, which probably represents a translational product of the additional 1.8-kb mRNA for factor H. This factor H was isolated from human plasma by means of immunoaffinity chromatography and high-performance liquid chromatography. When tested for its functional activity, this purified 43-kDa H protein was shown to act as cofactor for factor I- mediated cleavage of fluid-phase C3b to iC3b.

Antibodies, Monoclonal↗