The autosomal recessive mode of inheritance of C1r deficiency in a large Puerto Rican family

All living members of three generations of a large family with C1 r deficiency were studied. The two index cases showed undetectable C1 r and partial deficiency of C1 s associated with cutaneous, renal and joint disease as described previously (Moncada et al., 1972). The quantitative C1 q, C1 r and C1 s studies on the parents and the normal siblings were consistent with an autosomal recessive mode of inheritance for the C1 r trait.

There was more corrleation of the C1 r levels with the C1 s levels than with the C1 q levels, compatible with a linkage of the synthesis or catabolism of C1 s with C1 r.

Insulin and IgG complexes. An immunologic bypass for complement activation

Because of prior immunohistochemical findings of insulin, gamma globulin and complement components in diabetic microangiopathy, the in vitro interaction of insulin and IgG was studied. When native insulin and purified IgG were reacted under mild reducing conditions, a precipitate formed which was highly reactive with serum complement. Neither insulin nor IgG alone, reduced under the same conditions, demonstrated significant complement fixing activity. Maximal complement fixing activity was obtained from such a mixture at 30° C. in approximately one hour, the time of appearance of a visible precipitate. The presence of both insulin and IgG in the complement fixing precipitate was demonstrated by Ouchterlony analysis and by use of radio-labeled insulin and IgG. The tracer experiments indicated a precipitate composition of approximately 80 per cent insulin and 20 per cent IgG by weight. The utilization of complement components was similar to that obtained with IgG altered by heat aggregation or reaction with antigen. Complement fixation was not affected by alleviation of the precipitate, indicating that free sulfhydryl groups are not necessary. This interaction of denatured insulin and IgG to form a complement fixing complex offers a possible explanation for the presence of these components in micro-angiopathic lesions and may be a contributing factor to the pathogenesis of diabetic microangiopathy. Although complement is activated by an immunoglobulin insulin complex, this mechanism would be considered an immune bypass since specific antibody to insulin is not required.

Studies on the first component of complement (C1) and the inhibitor of C1 esterase in rheumatoid synovial fluids

The specific activity of C1 (haemolytic units per unit of C1q or C1s protein) was two to three times lower in synovial fluid of patients with sero-positive rheumatoid arthritis (RA) than in non RA or sero-negative RA fluids. These fluids contain a high ratio of C1s inhibitor to C1s. Experiments with radiolabelled C1s established that the C1s inhibitor in the synovial fluids of these patients is functional as it binds radiolabelled C1s. At the high ratios observed, it is possible that a complex of C1s and C1s inhibitor forms in these synovial fluids and alters the activation of the complement system. The potential for excess C1s inhibitor to slow or diminish complement utilization was shown by adding purified C1s inhibitor to serum in order to simulate the conditions in joint fluid (i.e. a high ratio of C1s inhibitor to C1s). Subsequent whole complement, C1 and C4 activites after incubation with selected immune complexes were higher as compared to controls without added inhibitor.

Ultrastructure of the human complement component, Clq (negative staining-glutamine synthetase-biologically active Clq)

The human complement component, Clq, is a fragile molecule of delicate structure consisting of three distinct parts, a central subunit, connecting strands, and terminal subunits. Each terminal subunit is further subdivided into a large and a small subunit, and the central subunit appears to be divided into two equal parts. In the intact molecule, six connecting strands link six terminal subunits by their larger subdivision to the central subunit. The overall diameter of the molecule when viewed from the "top" is about 35 nm (350 A).

Purification and Structural Studies of Human Clq

Human C1q has been purified by repeated precipitation at low ionic strength in the presence of chelating agents. The preparation was pure as judged by immunochemical and electrophoretic criteria. The final product had the biologic activities of C1q, but no detectable C1r or C1s activity. The yield of C1q by this method is about 40 to 60%.

Alternatively, C1q can be highly purified in smaller quantities for antigenic stimulation, using a single precipitation step, followed by two identical acrylamide gel steps. Rabbits antisera against this material were monospecific by immunodiffusion and immunoelectrophoresis, and agglutinated EAC1q cells, but not EA.

The molecular weight of C1q was estimated to be 388,000 on acrylamide gels containing SDS. C1q, lyophilized and dried to a constant weight, contained 13% nitrogen and its extinction coefficient, E1%1cm, was 6 to 6.5. Amino acid analyses and carbohydrate analyses have been carried out.

Ultrastructural Study of Clq

Purified C1q was diluted in buffer to between 10 and 50 µg/ml and droplets were placed on carbon-coated 400-mesh copper grids. Some grids were rinsed with dilute buffered formaldehyde or glutaraldehyde in order to fix the molecules. All grids were rinsed and stained in either 2% potassium phosphotungstate or 1% uranyl acetate. Approximately 200 photomicrographs from six different preparations were analyzed.

The whole C1q molecule is made up of an undetermined number of dense subunits which measure, on the average, 65 to 70 Å in diameter. These sub-units are joined at a central attachment area by strands estimated to be 60 to 100 Å in length and 15 to 20 Å in width. The structure of the central attachment area is hard to define, but is definitely less complicated than the central region of the IgM molecule.

Human Clr, Purification and Assay Based on Its Linking Role

C1, the first component of C, has been shown to be a macromolecule composed of three subunits, C1q, C1r, and C1s. Whereas C1q and C1s have been purified and monospecific antibodies have been produced against both, the C1r preparations used in most studies were only partially purified.

We developed a method of purification and assay for C1r. The purification procedure starts with a neutral euglobulin precipitation, followed by DEAE- and CM-cellulose chromatography, and a final preparative polyacrylamide gel electrophoresis.

Rabbits injected with this preparation produce monospecific precipitating antisera, which are capable of inhibiting C1 activity of cell-bound and fluid phase C1, but do not inhibit C1q or C1s.

The electrophoretic mobility of purified C1r is that of a β globulin on disc acrylamide electrophoresis at pH 8.6; its molecular weight, as estimated by Sephadex G-200 gel filtration, is 168,000.

The hemolytic assay of C1r in purified preparations is based on its property to link C1s to C1q and thereby generate macromolecular C1.

C1r, subunit of the first complement component: purification, properties, and assay based on its linking role

A method to obtain C1r, a subunit of the first complement component, in a highly purified state has been described for the first time. The stepwise method starts with a neutral euglobulin precipitation, after diethylaminoethyl- and carboxymethyl-cellulose chromatography and a final preparative polyacrylamide electrophoresis step. Such C1r preparations are devoid of C1q and C1s activities and show only one protein band on analytic polyacrylamide electrophoresis. Rabbits injected with this preparation produced antisera showing only one precipitation band. The stability of C1r activity was determined under different conditions, and C1r was found to be labile at 37 degrees C, pH 7-8 and low ionic strength. The electrophoretic mobility of purified C1r is that of a beta-globulin on disc acrylamide electrophoresis and on agarose electrophoresis at pH 8.6. Its molecular weight as estimated by sephadex chromatography is 168,100.A sensitive hemolytic assay based on the property of C1r to link C1s to C1q and thereby to generate macromolecular C[unk]1 is described. The number of C[unk]1 molecules generated is stoichiometrically related to the concentration of C1r for a fixed C1q and C1s concentration provided that the titration is carried out below the plateau zone. Macromolecular C1 can be separated from free C1s as the former is cell bound. This method of purification and assay should allow the development of monospecific antisera and further chemical study of C1r.

Sub-units of the first complement component in immunologic deficiency syndromes: independence of Cls and Clq

Normal concentrations of C1 esterase, C1s, have been found in nineteen individuals with a variety of immunologic deficiency syndromes. C1q levels are markedly low in patients with lymphopenic hypogammaglobulinaemia. The lack of correlation of serum concentrations of C1s with C1q in several patients suggests a separate mode of synthesis or catabolism for these C1 subunits. Furthermore, the extreme C1q deficiency in lymphopenic hypogammaglobulinaemic patients may play a role in their serious prognosis; however the normal C1s concentrations would allow some complement mediated functions.

A Method for Preparing Monospecific Antisera to C1 Esterase (C1s): Microheterogeneity of Purified C1s

Highly purified C1s has been obtained by immunization of rabbits using popliteal node injections of highly purified C1s followed by booster injections with gel segments containing C1s after disc-acrylamide gel electrophoresis. The antisera are monospecific and unexpectedly reveal electrophoretic microheterogeneity in highly purified C1s preparations. We have studied this electrophoretic heterogeneity in highly purified and in crude C1s preparations and hypothesize that it is due to two factors: 1) The partial proteolysis of C1s produced either by other serum enzymes or perhaps by autocatalysis. This can be demonstrated in highly purified C1s preparations. 2) The presence in crude preparations of another serum protein(s) which appears to influence the migration of C1s. These antisera are useful for quantitating C1s by single radial diffusion. We consider the heterogeneity of C1s to be an important feature of this molecule and future quantitative studies should take account of it.

Immunochemical Quantitation of Human C1 Esterase (C1s): Concentration in Normal Serum and Purification Yields

Immunochemical quantitation of C1s is possible with the single radial immunodiffusion technique. C1s is the complement component with the lowest concentration for which this technique has been used. The normal adult concentration is 32.8 ± 6.2 µg/ml (1 S.D.). The C1s concentration in normal human serum is relatively insensitive to the method of storing and collecting blood samples. Sera or EDTA plasma can be kept at 0°C, -20°C or -70°C, so this should be a practical method for clinical laboratories. Clinical studies in various disease states are in progress. Using this method, the recovery and overall yield at each stage of purification as well as the specific hemolytic and esterase activities were calculated. The overall yield of C1s averaged 3% to 4% with specific hemolytic activities of 150,000 to 350,000 site-forming units/mg, and specific esterase activities ranging from 1500 to 2500 units/mg. These figures are the best obtained to date, but with increasing knowledge of this important serum enzyme more rigid criteria of purification are being determined with the goal of achieving high constant specific activity. The yields at various steps should be helpful in redesigning the methods of purification.

Deficiency of C1r in human serum. Effects on the structure and function of macromolecular C1

THE EXPERIMENTS PRESENTED HERE UTILIZE A HUMAN SERUM MARKEDLY DEFICIENT IN HEMOLYTIC COMPLEMENT ACTIVITY TO SHOW THAT: (a) The hemolytic deficiency is the result of a selective deficiency in hemolytic C1. (b) The relative absence of hemolytic C1 is due to a profound deficit in C1r function associated with less than normal C1s protein and hemolytic function and normal C1q protein concentration and function. This deficit in C1r in the face of normal C1q suggests that different cell types are responsible for the synthesis of each of these components. (c) Whatever the basis for the deficiency of C1r function, this defect results in an inadequate association of the remaining C1 subcomponents, C1q and C1s, even in the presence of calcium ions, thus suggesting that C1r has an important role in the assembly and/or maintenance of macromolecular C1.