Detection and quantitation of circulating immune complexes by the C1q-protein A binding assay (C1q-PABA)

Excessive hypercalcaemia and mixed connective tissue disease

A 23-year-old female with extreme hypercalcaemia was treated with calcitonin, mitramycin and parathyroidectomy and normocalcaemia was achieved after 4 weeks. Nevertheless, the patient later died of cutaneous necrosis, impaired circulation and multiple organ failure. Serum immunoreactive parathyroid hormone was in the normal range and parathyroid tissue normal. Mixed connective tissue disease was diagnosed on the basis of high titers of antibody to extractable nuclear antigen, moderately elevated levels of antibody to nuclear antigen and only marginal elevation of anti-double standed DNA. The role of Cl. difficile toxin in the blood and an acinic cell tumour is unclear.

Plasma concentrations of complement split product C3d and immune complexes after procainamide induced production of antinuclear antibodies

Seventeen patients treated with procainamide for cardiac ventricular arrhythmias were followed for up to 40 weeks. Immunological data as a clue to developing the systemic lupus erythematosus (SLE)-like syndrome was emphasized. Ten patients developed antinuclear antibodies (IgG or IgM), but no increase in the plasma concentration of the complement split product C3d or immune complexes, measured by two different methods, was demonstrated. This finding is in contrast to the high levels of both C3d and immune complexes in SLE. The discrepancy may be caused by a lack of immune complex mediated complement activation by the procainamide induced antibodies, or may be due to a difference in severity of disease. The acetylator phenotype of the patients was determined but due to the low frequency of fast acetylators no comparison of the immunological response of the two phenotypes could be done.

Hereditary, complete deficiency of complement factor H associated with recurrent meningococcal disease

Complement factor H (beta-1H globulin) is an important regulatory protein which inhibits the spontaneous complement activation via the alternative pathway. We describe a 15-year-old girl without any detectable factor H in plasma. She has had two episodes of meningococcal disease, but is otherwise completely healthy. Secondary to the factor-H deficiency, the levels of factor B, properdin, C3, and C5-C9 were strongly reduced due to spontaneous in vivo activation of the alternative complement pathway. Plasma C3dg was strongly elevated in spite of the factor-H deficiency; apparently erythrocyte CR1 substitutes for factor H in C3 degradation. Neither C3 nor complement lesions were demonstrable on her erythrocytes which did, however, show increased, spontaneous haemolysis in vitro in citrate plasma, but not in serum. The patient is a single child and her parents, who are unrelated and healthy, had half-normal levels of factor H. This reduction of factor H is sufficient to cause increased, spontaneous activation of the alternative pathway.

Immune complex assays: diagnostic and clinical application

The presence of circulating immune complexes have been described in many different human disease states but the significance of their presence has always been a subject for debate. Improvements in the methods of detecting immune complexes have demonstrated a wide degree of heterogeneity, which accounts for the difficulty in obtaining accurate and reproducible measurements, even in the same individual. Techniques for isolating individual complexes, characterizing their pathophysiological properties, and biochemically analyzing the nature of the complexed antigen are now being used to provide data that is helping to clarify the role of immune complexes in the pathogenesis of disease. In addition, such studies are also providing data which is proving that immune complexes have a potential role in immune regulation.

Passage of undegraded dietary antigen into the blood of healthy adults. Quantification, estimation of size distribution, and relation of uptake to levels of specific antibodies

The absorption into the blood of ovalbumin (OA) and beta-lactoglobulin (BLG) was investigated in eight healthy adults. Enzyme immunoassays showed up to 10.5 ng OA/ml serum in seven out of eight individuals 2-3 h after a test meal, whereas no BLG was demonstrated. The apparent size distribution of the absorbed OA was investigated by high-pressure liquid gel permeation chromatography fractionation, followed by enzyme-linked immunosorbent assay, which in the fractionated sera showed OA in all eight individuals. OA was found at the elution volume of intact OA and, in addition, was present in high molecular weight fractions, as part of the immune complexes. The serum concentrations of OA could not be clearly correlated to levels of serum and secretory anti-OA antibodies. No significant alterations of the levels of circulating immune complexes could be demonstrated by two antigen-nonspecific assays. The presented data indicate that, for certain dietary proteins, low-grade absorption of apparently undegraded protein into the blood occurs regularly in healthy adults.

C3 nephritic factor in a patient with recurrent Neisseria meningitidis infections

A 15-year-old female experienced two systemic infections with N.meningitidis (group C and B) within a two months period. Classical as well as alternative pathway CH50 determinations on the patients serum showed no lysis. All individual complement factor concentrations, except for C3, were found to be within the reference area. Crossed immunoelectrophoretic analysis of C3 revealed no demonstrable native C3. The patient had normal levels of C3c and a markedly elevated C3d concentration. Serum from the patient was found to convert all native C3 in normal sera within 10 minutes at 37 degrees C. The active converting principle, present in the IgG fraction activated C3 in C4-depleted serum, and had a dose dependent stabilizing effect on the EA-C3bBb complex. The isolated factor showing the characteristics of C3 nephritic factor (C3 NeF), was unchanged in the patients serum over a ten months observation period. Circulating immune complexes (IC) could not be demonstrated by a C1q-dependent assay but the patients capacity to solubilize preformed IC in vitro was virtually abolished. The patient had no signs of renal disease or lipodystrophy.

Influence of serum complement and rheumatoid factor on detection of immune complexes by the C1q and monoclonal rheumatoid factor solid-phase assay

Soluble purified monoclonal and polyclonal rheumatoid factor, total serum complement, and soluble C1q all inhibit the detection of model tetanus toxoid/anti-toxoid immune complexes in the solid-phase C1q assay. The binding of these immune complexes to solid-phase monoclonal rheumatoid factor is less inhibited by soluble C1q and by total serum complement, but clearly decreased by soluble monoclonal or polyclonal rheumatoid factor. Serum complement does not reduce the size of these model complexes. We recommend the use of low ionic strength EDTA (10 mM) to partly neutralize the complement-mediated inhibition. This procedure is shown to be superior to currently used higher EDTA concentrations and to the use of IgG-Sepharose.

Reactions of immunoglobulin G-binding ligands with platelets and platelet-associated immunoglobulin G

Immunoglobulin G (IgG) bound to platelets is usually detected by one of two general methods: binding of labeled anti-IgG or consumption of anti-IgG. The latter method gives, in general, values 5-10-fold greater than the former under the same conditions. To investigate these discrepancies, we have compared the detection of platelet-bound IgG by a labeled anti-IgG binding assay and by a quantitative antiglobulin consumption test using the same antibodies. The interaction of 125I-labeled monoclonal anti-IgG or polyclonal anti-IgG with washed and IgG-coated platelets was studied. The binding of these ligands to washed normal platelets was largely (50-80%) nonspecific; the binding was not saturable and was only partially inhibitable by excess unlabeled anti-IgG. The binding of anti-IgG to platelets coated with anti-PIA1, a platelet-specific IgG antibody, appeared to be saturable and inhibitable; the dissociation constant (KD) of this IgG-anti-IgG reaction was 4.9 X 10(-9) for monoclonal and 1.4 X 10(-7) for polyclonal anti-IgG. The ratio of sites present on the membrane (determined by 131I-labeled anti-PIA1) to the number of binding sites for anti-IgG determined by Scatchard analysis was 0.53 for monoclonal anti-IgG and 1.3 for polyclonal anti-IgG. The binding of monoclonal anti-IgG to platelet-bound immune complexes or IgG aggregates appeared to be complex. 131I-Labeled IgG was affixed to platelets and was detected by three tests: direct binding of radiolabeled monoclonal anti-IgG and quantitative antiglobulin consumption (QAC) tests, which were quantitated either by measuring directly the amount of radiolabeled anti-IgG consumed from fluid phase (direct QAC), or indirectly by reference to a calibration curve relating the consumption of anti-IgG by known amounts of fluid-phase, non-immune IgG (indirect QAC). The amount of platelet-bound IgG detected by the direct binding of 125I-labeled monoclonal anti-IgG and by the direct QAC approximated that known to be bound to the platelet. The results of the indirect QAC test were 10-fold greater. The discrepancy appears to be due to the fact that there is a difference between the IgG-anti-IgG interaction when IgG is bound to a platelet and when it is in solution or bound to plastic nonspecifically or specifically. This difference results in a falsely high value for platelet-bound IgG when fluid-phase or plastic-bound IgG is used to calibrate the antiglobulin consumption test.