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PubMed1976

Cooperative binding of a complement component to antigen-antibody complexes. III. Complexes containing IgM antibodies.

The first component of guinea pig complement (C1)2) is bound in a cooperative manner to antigen-antibody complexes containing rabbit IgM antibodies, as was previously shown to be the case for IgG antibodies. The shape of the binding curves is consistent with an allosteric mechanism involving clusters of 10 interacting C1 binding sites. Similar results were obtained with IgM antibodies against an artificial hapten and against a natural constituent of the erythrocyte membrane.

Allosteric Regulation↗
PubMed1977

Further studies on the identification of the subcomponents of the first component of complement after affinity chromatography of human serum on IgG-sepharose.

Affinity chromatography of serum on IgG covalently linked to Sepharose results in the retention of the proteins of the first component of complement (C1). A fraction called pool II is eluted from this column with 0.025 M EDTA and has previously been shown to contain C1s and a novel protein believed to be part of the C1 complex and called C1t. C1r has now been located in pool II and these three proteins were purified by DEAE cellulose chromatography. C1r and C1s were recovered in the proenzyme form and their identity was established by SDS polyacrylamide gel electrophoresis before and after reduction and alkylation, and on the basis of their esterolytic activities toward different substrates. The properties of C1r from pool II are contrasted with those of the protein recovered from the pool III eluate of the affinity column and previously thought to be C1r.

Chromatography, Affinity↗
PubMed1976

Studies on vasculitis. VII. C-reactive protein as a substance perpetuating chronic vasculitis. Occurrence in lesions and concentrations in sera.

Previous findings were confirmed that C-reactive protein (C-RP) occurs in some vasculitis lesions, particularly those infiltrated mainly by neutrophils (necrotizing vasculitis). The C-RP was usually in lesions also containing complement C1 or C3c, and in some, IgG was present. Using a procedure that reliably detected 200 ng C-RP/ml serum, C-RP was found in sera of many normal persons, and the amount was influenced by the occupation of the donor. Sera of thirty-one persons with vasculitis with mainly mononuclear cell-infiltrated lesions had about four-fold more C-RP (mean 28, 200 ng/ml serum) than found in normal persons, and sera of thirty-nine persons with mainly neutrophil-infiltrated lesions had eight times the normal amount (mean 56,400 ng C-RP/ml). The amount of C-RP was influenced by the severity, extent and duration of the disorder in most patients. Experimental data suggests that C-RP may contribute to the perpetuation of inflammation in chronic vasculitis.

Animals↗
PubMed1978

Demonstration and quantitation of activation of the first component of complement in human serum.

Activation of the first component of human complement (C1) in human sera can be readily detected in double immunodiffusion studies with anti-C1q, anti- C1r, and anti-C1s as it produces a characteristic pattern quite different from that of precursor C1. Native macromolecular C1 gives a continuous line of precipitation with antisera to C1q, C1r, and C1s in double diffusion studies. After activation of C1 by incubation of serum with complement activators, three major changes occurred in the Ouchterlony pattern. First, spurring of the C1s precipitin line over that of macromolecular C1, indicating release of C1s from C1, was observed with low doses of activator. Release of C1s was quantitated by single radial diffusion and shown to be complete with the highest activator dose examined. Second, C1q was released with larger activator doses as shown also by spurring of the precipitin line due to this component over the remaining macromolecular C1. Third, and most surprising, C1r antigenicity was progressively lost as the activator dose was increased and no C1r line remained with the highest dose of activator tested. This was not true with C1s as there was no change in the total C1s concentration in serum incubated with various activator doses. These observations provide two approaches to the quantitation of C1 activation in human serum. First, C1r and C1s can be quantitated by single radial diffusion. A decrease in the C1r:C1s ratio correlates with activation. Second, C1s released by the activation can be quantitated by single radial diffusion if the agarose contains high concentrations of anti-C1q to confine C1, also containing C1s, to the area near the application well, and lesser concentrations of anti-C1s to permit free C1s to produce a measurable ring. The extent of release of C1s also correlates with activation. These immunochemical techniques to quantitate C1 activation directly inserum do not require specialized reagents. It is hoped that they will be useful in screening pathological sera and in monitoring the status of the complement system in patients.

Complement C1↗
PubMed1976

Inactivator of the first component of human complement (C1INA). Enhancement of C1INA activity against C1s by acidic mucopolysaccharides.

Acidic mucopolysaccharides enhanced C1INA activity against C1s. The presence of heparin in the reaction mixture of C1INA and C1s markedly enhanced the inactivation of C1s by potentiating C1INA activity. Treatment of serum with C1s resulted in the inactivation of C4 hemolytic activity, but this inactivation of C4 by C1s was prevented by the presence of heparin presumably due to the enhancement of C1INA activity normally present in serum. The other acidic mucopolysaccharides, chondroitin sulfates A, B and C, were also effective on potentiating C1INA activity against C1s, but they were less active than heparin. The enhancement of C1INA activity by heparin was not observed in the reaction between C1INA and plasmin.

Chondroitin Sulfates↗
PubMed1977

Circulating immune complexes detected by 125I-Clq deviation test in sera of cancer patients.

The presence of circulating immune complexes in freshly drawn sera of patients with various forms of malignancies was detected by the 125I-Clq deviation test of Sobel et al. More than 50% of the 459 cancer sera showed a high inhibition of 125I-Clq uptake by sensitized sheep erythrocytes when compared with sera of 50 healthy laboratory personnel. The levels were compared with levels of total hemolytic complement and immunochemical determinations of Cl1 and C3. A correlation between high levels of circulating immune complexes and low levels of Clq was suggested. These immune complexes were separated by sucrose density gradient ultracentrifugation at low pH and were found to be heavier than 19S. Fluctuation of levels of immune complexes was evident when serial samples from the same patient were tested. Decrease of levels of immune complexes and a concomitant increase of Clq were detected after Calmette-Gueérin bacillus and autologous tumor cell treatment in some melanoma patients.

Antigen-Antibody Complex↗
PubMed1976

Detection of circulating antigen-antibody complexes by their inhibitory effect on the agglutination of IgG-coated particles by rheumatioid factor of Clq.

The agglutination of Ig-coated particles by human RF or Clq can be inhibited by Ig aggregates or AgAb complexes. The effect of Ig class was studied by means of agarose-linked human monoclonal Igs. RF was inhibited by all subclasses of IgG and IgA but not by IgM, whereas Clq reacted with IgM, IgG3 and IgG1. Heat-aggregated IgG3 was fractionated by gel-filtration on Ultrogel. Inhibition was restricted to certain fractions of aggregates, viz (IgG3) approximately 7 and (IgG3) approximately 21 for RF, and (IgG3) approximately 10, (IgG3) approximately 14 and (IgG3) approximately 27 for Clq. In a precipitin curve experiment, it was found that RF was inhibited by soluble complexes over an extended range of AgAb ratios, the inactivation of Clq being limited to complexes with 2-5 times antigen excess. Inhibiting factors were found in patients with various diseases and, at low titres, in 22% of healthy people. In 27% of patients' sera, the inhibitors were demonstrable by Clq only after removal of endogenous RF by adsorption on insolubilized IgG. In several patients endogenous agglutinating activity and direct inhibitory activity tended to alternate during the course of the disease. Sera from various patients were also filtrated on Ultrogel and the elution was monitored by immunoassay of IgA, IgM and IgG, as well as by the two inhibition tests. The inhibiting factors were distributed over several peaks which only partially coincided with the elution profiles of IgG and IgM.

Agglutination Tests↗
PubMed1978

Direct demonstration and quantitation of the first complement component in human serum.

The first component of complement, C1, can be demonstrated and quantitated in normal and pathological human serums by simple immunochemical techniques. All of the C1q, C1r, and C1s detected in normal serum was found to be in the C1 complex. A simple modification of these methods permitted the quantitation of free C1s in the presence of macromolecular C1, a technique which may prove useful in screening pathological serums.

Calcium↗
PubMed1976

Reversible binding of a T cell factor on IgG-coated sepharose beads.

Supernatants of alloantigen-activated T cells contain a number of factors, including an immunoglobulin-binding factor (IBF) which inhibits complement-induced hemolysis of sheep erythrocytes coated with anti-Forssman IgG antibodies and a factor which suppresses IgM antibody synthesis in vitro. These two factors may be identical, since they are simultaneously retained on Sepharose beads to which IgG has been coupled and can be recovered by elution at pH 2.8. They do not bind to Sepharose beads to which IgM of F(ab')2 fragment of IgG has been coupled, demonstrating that they have a selective affinity for the Fc region of IgG. In addition, the fixation of IBF on the Fc portion of IgG reversibly inhibits subsequent binding of the first component of complement (C1), thus indicating that IBF does not irreversibly alter the C1 binding site(s) of IgG.

Animals↗