Particle counting immunoassay (PACIA). II. Automated determination of circulating immune complexes by inhibition of the agglutinating activity of rheumatoid sera

Particle counting assay for anti-toxoplasma IgG antibodies. Comparison with four automated commercial enzyme-linked immunoassays

An assay for anti-toxoplasma IgG antibodies based on agglutination of latex particles was set up and compared with commercial immunoassays. The reaction was measured by instrumental counting of particles remaining unagglutinated. The running time was 45 min. This test (PaC) was compared using 243 serum samples with four automated commercial immunoassays: the Enzymum test Toxo IgG (ES300, Boehringer), the Vidas Toxo IgG (Biomérieux), the IMX Toxo IgG (Abbott), the Magia Toxoplasma gondii IgG (Merck). The mean values (+/- SD) obtained by IMX (25 IU +/- 68) and ES300 (45 IU +/- 142) were significantly lower than the values obtained by Vidas (73 IU +/- 237, p < 10(-4) and p = 0.006, respectively), by Magia (80 IU +/- 300, p < 10(-4) and p = 0.0005) and by PaC (70 IU +/- 260, p < 10(-4) and p = 0.0126). The correlations between PaC and Toxo IgG Boehringer, Biomérieux, Abbott, Merck were r = 0.97, r = 0.98, r = 0.94, r = 0.98, respectively. The correlation coefficients between the enzyme-immunoassays ranged from 0.96 to 0.99. All positive samples by PaC were found to be positive by enzyme-immunoassays except for eight sera which were doubtful positives by the Enzymum test ToxoIgG from Boehringer. No negative sample by PaC was found positive by any of the enzyme-immunoassays. In PaC, when two latex preparations coated with different antigen were compared, the correlation was rather weak (r = 0.93) suggesting that the selection of the antigen can be critical. In conclusion, the four automated commercial immunoassays now available gave similar results. However, the discrepancies observed in this study underlined the importance of clinical and biological follow-up of the patients and the necessity to confirm the result. The introduction of a new technique such as PaC, which is now available for a large variety of assays in Clinical Chemistry and Microbiology, is justified by its intrinsic advantage of homogeneity. Therefore, automation is easy as well as the control of possible interference.

Immunoassay by particle counting for coagulation testing: application to the determination of antithrombin III, von Willebrand factor antigen (vWF:Ag) and plasminogen

Based on immunoassay by particle counting, three methods for antithrombin III, von Willebrand factor and plasminogen were developed on an automated IMPACT machine and on a semi-automated MULTIPACT system. Precision of the techniques, measured at low, medium and high level of the calibration curve showed coefficients of variation varying from 4.3 to 13.8%. Accuracy was evaluated by dilution recovery test and by correlation with rocket immunoelectrophoresis and chromogenic substrate techniques. The results show that the proposed methods correlate well with existing techniques and that immunoassay by particle counting is applicable to several coagulation tests.

Coexistence of free antigens, free antibodies and immune complexes in sera from patients with suspected deep-seated candidosis

Two commercially available latex agglutination tests: Cand-TEC(TM) from RAMCO Laboratories, Inc., Houston, Texas, USA, for the detection of a heat labile Candida antigen, and LA-Candida Antigen Detection System from Immuno-Mycologics (IMMY), Inc., Norman, Oklahoma, USA, for the detection of Candida mannan antigen, and Own LAT, a self-prepared latex agglutination test for the detection of Candida mannan antigen were tested on 467 sera of patients at risk for deep-seated Candidosis. Separate, parallel investigations were made to demonstrate anti-Candida antibodies (3 methods), circulating immune complexes (not antigen-specific, 2 methods), and rheumatoid factor (2 methods). Specificity and sensitivity of the mannan antigen detection systems were studied. Conditions of specific and non-specific mannan binding to antisera were studied in a defined mannan-antiserum system. The potential and the limitations of the Candida mannan antigen and protein antigen detection systems using latex particle agglutination are evaluated.

A latex agglutination test for the detection of canine parvovirus and corresponding antibodies

Latex particles coated with rat monoclonal antibodies directed against a canine parvovirus are agglutinated by the virus antigens. In this study, the reaction was quantitated by a technique which had been described as immunoassay by particles counting. The method is as sensitive as a radioimmunoassay with the same antibody, but has the advantages of simplicity and safety. It allows the detection of parvoviral antigens to 4 ng/ml. Incubation of these antigens with specific antibodies resulted in inhibition of the agglutination reaction. By this procedure the presence of antibodies against canine parvovirus can be detected to a concentration of 150 ng/ml. The system can be easily automated, thus increasing reproducibility. This latex agglutination technique can be performed as a slide test; and although this method is 4-5 times less sensitive, it could be useful in field studies, for the detection of the viral antigens and the corresponding antibodies.

Quantitation of human chorionic gonadotrophin by the planimetry of latex agglutination-inhibition results on microtiter plates

A new type of heavy latex particle (LP) coated with the conjugates of human chorionic gonadotrophin (hCG) and bovine serum albumin (BSA) was used as indicator for the microtiter agglutination-inhibition assay of hCG using a monoclonal antibody (McAb) to hCG. The precipitation patterns of LP were measured by an automatic planimetry system. The detection limit of this method was 4 to 8 IU/l. Human luteinizing hormone (hLH) and follicle-stimulating hormone (FSH) caused hardly any cross-reaction in the presence of 3,350 IU/l and 1,500 IU/l, respectively. This planimetric immunoassay (PMIA) method provides a potentially useful method for hormone assay.

Immune-induced vascular connective tissue alterations in rabbits chronically immunized with bovine serum albumin: biochemical studies on collagen, glycosaminoglycans, RNA, and DNA in normal and injured aorta

Repeated intravenous injections of bovine serum albumin in rabbits caused a significant reduction in the aortic in vivo biosynthesis of chondroitin-4,6-sulfate, whereas no changes were observed in the synthesis of other glycosaminoglycans nor in the content of collagen. This contrasts the biochemical changes generally seen in acute vascular injury. When experimentally elicited vascular injury and repair processes were induced in chronically immunized rabbits, the proliferative response was greatly inhibited, as reflected by a significant diminution of the DNA amount. Also, the vascular connective tissue matrix repair was restrained: the aortic content of collagen and the collagen type III/I ratio was repressed, and the in vivo biosynthesis of sulfated glycosaminoglycans was markedly reduced. All immunized rabbits developed antibodies to bovine albumin, but in only a few were circulating immune complexes detected. The inhibitory effect of persistent immunostimulation on the nonspecific processes of repair in vascular connective tissue may be of significance as to chronicity of vasculitis, as well as inflammation and repair in general, in inflammatory connective tissue diseases.

Monitoring and tentative diagnosis of herpetic encephalitis by protein analysis of cerebrospinal fluid. Particular relevance of the assays of ferritin and S-100

The cerebrospinal fluid (CSF) of 9 patients with herpetic encephalitis was analyzed by particle counting immunoassay of ferritin, S-100, immunoglobulins, anti-herpes antibodies and immune complexes and by electrophoresis for the detection of oligoclonal bands. The main conclusions are: first, the simultaneous increase of both ferritin and S-100 in the presence of symptoms of encephalitis suggests strongly the infection is herpetic; second, high and increasing levels of S-100, probably related to the extent of the necrotic process, indicate a poor prognosis. In addition, 8-14 days after onset, locally produced anti-herpes antibodies were detectable, the IgG index increased and oligoclonal bands became visible.

Feasibility of extracorporeal on-line large-scale plasma adsorptions on protein A-sepharose columns in cancer patients

The feasibility of extracorporeal adsorption of 1.5-3 L plasma on protein A-Sepharose was investigated in six patients with advanced cancer. Anticoagulation with heparin was associated with respiratory distress syndrome in two patients, most likely caused by complement activation as indicated by a transient leukopenia during plasma reinfusion and appearance of C3 degradation products in the extracorporeal circulation. Addition of citrate abolished the respiratory symptoms, C3 degradation, and leukopenia, and no adverse reactions were observed. No objective tumor regression was observed in any of the patients. Three patients progressed during therapy. In one of these, multifocal central tumor necrosis was observed as a possible, although unproven, therapeutic effect. Increased natural killer and/or killer cell activities were recorded in three patients and increased complement-dependent serum cytotoxicity in one patient. The level of circulating immune complexes decreased significantly (18-28%) in three patients studied. It is concluded that extracorporeal plasma adsorption on protein A-Sepharose is feasible when citrate is added to the extracorporeal system, but its therapeutic efficacy is uncertain.

Immune complexes in cerebrospinal fluid and serum of neurological patients. Possible intrathecal formation in bacterial meningitis and herpetic encephalitis

We assayed immune complexes (IC) by Particle Counting ImmunoAssay in the serum and cerebrospinal fluid (CSF) of patients with various neurological disorders. In pyogenic meningitis, the levels of IC sharply increased 4-8 days after onset with a fall before the 10th day of the disease. In herpetic encephalitis the IC and antibody levels started to increase about 12 days after onset. The IC persisted at high values for 3-4 weeks, whereas the high antibody titers persisted for several months during the follow-up. In these 2 groups of patients IC were probably locally produced as indicated by the lack of correlation with the IC levels in the serum. We did not detect any significant increase of IC in the serum and CSF of patients with multiple sclerosis (N = 48) or with acute idiopathic polyradiculoneuritis (N = 11). Using another technique based on the determination of IgG and C4 in polyethylene glycol precipitates we also failed to detect any significant increase of IC in multiple sclerosis sera.

A modified microcomplement fixation test for antigen or antibody determination in soluble immune complexes, using gel filtration

A Modified Microcomplement Fixation Test (MMFT), useful for detecting and quantifying soluble immune complexes (ICs) and their components in chromatographic separations, is described. This method is based on the addition of excess specific antibody to the ICs against any of their components in order to increase the ICs' anticomplementarity. The concentration of ICs is expressed as the sample dilution which fixes 50% of the added Complement. The MMFT was applied to profiles of ICs obtained in vivo and in vitro. MMFT allows great sensitivity, good reproductibility and the detection of noncomplement fixing ICs without any interference of free antigen (Ag) or free antibody (Ab).

Autoantibodies, immune complexes and HLA-D in thyrogastric autoimmunity

Forty-one patients with Hashimoto's thyroiditis (HT) and 82 with Pernicious anaemia (PA) were investigated. All 123 patients were HLA-D typed and results correlated to thyroglobulin antibodies (TgAB), microsomal antibodies (MAb), parietal cell antibodies (PCA), circulating immune complexes (IC), and intrinsic factor antibodies (IFA). In PA, TgAb was found less frequently in Dw2 positive patients than in Dw2 negative patients. IFA was rarely found in Dw5 positive PA patients. In HT, patients positive for Dw5 had lower levels of TgAb. IC were present in 67% of patients with HT, but only in 2.5% of patients with PA (p less than 0.01). Dw5 was associated with low levels of IC in HT. In conclusion, HT and PA seem to be related by their association with HLA-D types, but a heterogeneity in the pattern of antibodies and IC could be seen. The organ specific antibodies characteristic for each disease were present in lower levels in patients with Dw5.

Circulating immune complexes in Hashimoto's thyroiditis. Correlation to HLA and autoantibodies

Circulating immune complexes (IC) were determined in sera from 41 patients with Hashimoto's thyroiditis by a polyclonal rheumatoid factor (pRF) assay based on the inhibition of the agglutination of IgG-coated latex particles. Elevated levels of IC were found in 63% (26/41) of the sera. There was a significant correlation (Rho = 0.91, P less than 0.001) between results obtained before and after treatment of sera with dithiothreitol (DTT). By precipitation with 2.5% polyethylene glycol (PEG) before pRF inhibition assay, the activity of IC was found in only 7% (3/41) of the sera. Size chromatography studies of the sera showed the inhibitory activity predominantly in the intermediary region. When found in the IgM-region the activity was not reduced by DTT. By use of a polyethylene glycol complement consumption test (PEG-CC) the occurrence of IC was 10% (4/41). It was not possible to find any correlation between the detectable IC and the presence of microsomal, thyroglobulin, or thyroid-stimulating antibodies. Based on our studies the sizes of IC seemed to be heterogeneously distributed and the majority were not precipitated by PEG (2.5%), final concentration). The antibodies involved in the formation of complexes seemed to be of IgG or IgA classes. HLA-D typing of the patients showed a non-significant association between HLA-Dw5 and low levels of IC while the presence of HLA-Dw4 was significantly associated with a high level of IC (P less than 0.05).

Quantitation of DNP, digoxin, HCG and anti-DNP antibody by electronic data processing of latex antiglobulin reaction results

Volumes of agglutinates produced by the microtiter latex antiglobulin test (LAGT) were measured by an electronic data processing (EDP) method using a particle volume distribution analyzer. This method proved highly sensitive for quantitating weak antibodies, such as anti-digoxin and anti-DNP. EDP measurement of the microtiter latex antiglobulin-inhibition test (LAGIT) is also a suitable method for quantitating HCG, digoxin and DNP.

Discrepancy between haemagglutination and radioimmunological techniques for measurement of serum thyroglobulin autoantibodies

Recently, it has been suggested that in some patients with autoimmune thyroid diseases the tanned red cell (TRC) method for detection of thyroglobulin autoantibodies (TgAb) is negative where TgAb measured by radioimmunoassay (RIA) show positive values. To investigate this further, patients with thyroid diseases, pernicious anaemia and a control group were studied for serum concentrations of TgAb by TRC and by quantitative RIA, calibrated against MRC Standard A65/93. Antibodies for microsomes (MAb) were measured immunofluoretically. There was in all patient groups (Hashimoto's thyroiditis (n = 41), Graves' disease (n = 50), idiopathic myxoedema (n = 12), euthyroid Graves' disease (n = 7), pernicious anaemia (n = 81) a discrepancy between TgAb measured by TRC and RIA, respectively, whereas there was a reasonable correlation between the presence of TgAb by RIA and the presence of MAb. A possible interference from antinuclear antibodies and rheumatoid factors was ruled out. There was no increased frequency of TgAb measured by RIA in the control group. Fractionation of TRC negative sera revealed macromolecular TRC-activity, whereas TgAb positive sera by both methods had almost exclusively RIA and TRC activity corresponding to IgG. Based on these results and others it seems that the TRC method for measurement of serum TgAb is of limited diagnostic value. Furthermore, the TRC method is in many cases not sensitive enough for screening for TgAb prior to measurement of serum Tg, which is of importance as this method shows false values in the presence of TgAb due to methodological interference.

The concentration of IgM in the cerebrospinal fluid of neurological patients

The level of IgM was determined by Particle Counting Immunoassay in the cerebrospinal fluid. In non-neurological patients (N = 20) the mean was 97.5 micrograms/l with the upper reference limit at 380 micrograms/l. The mean IgM index was 0.021 with the upper reference limit at 0.071. Of 21 patients with stroke, 5 had an IgM index exceeding the reference limit. High levels and indices of IgM were observed in most patients (N = 27) with infectious meningo-encephalitis. In this group, the IgM index was abnormal in about 30% of cases with a normal total protein content, and was more often increased than the IgG index. In multiple sclerosis patients (N = 80), the IgM index was increased in 32%. In this disease very high values of IgM index (greater than 0.13) were never associated with very high values of IgG index (greater than 1.8). A significantly higher proportion of males was found in the group of patients with very high values of IgM index (N = 11). No significant influence of the age of onset, the interval between onset and sampling and clinical state was observed. However, of 10 patients with a multiple sclerosis history exceeding 15 years none had an IgM index exceeding the upper reference limit. Four patients with multiple sclerosis had a high IgM index without either an increase of the IgG index or the presence of oligoclonal bands.

Comparison of renal function and psychomotor performance in workers exposed to elemental mercury

Renal function and psychomotor performance (eye-hand coordination, arm-hand steadiness) of a group of 43 workers exposed to mercury vapor were examined. Their mean age an average duration of exposure to mercury were 38 and 5 years, respectively. The results were compared with those in a matched group of 47 control workers. Increased proteinuria and albuminuria were found slightly more prevalent in the Hg-exposed group than in the control workers. These results are in agreement with those found during a previous study carrier out in another group of workers also exposed to elemental mercury (Buchet et al. 1980). The scores of the psychomotor tests were less satisfactory in the Hg workers than in the control workers, the arm-hand steadiness test being more discriminative than the eye-hand coordination test. Preclinical changes in psychomotor function can be detected independently of the presence of signs of renal dysfunction. No clear-cut relationships were found between the prevalence of abnormal psychomotor scores and the level of mercury in blood (HgB) or in urine (HgU). Increased prevalences of abnormal psychomotor scores seem however to occur for HgB between 1 and 2 micrograms/100 and for HgU between 50 and 100 micrograms/g creatinine. Therefore, a biologic threshold limit value of 50 micrograms/g creatinine in proposed for urinary mercury to prevent the development of preclinical effects on the central nervous system. A similar critical HgU level based on renal dysfunction prevalences has been suggested in a previous study.

Studies on hypersensitivity to bacterial antigens in intrinsic asthma

Twelve children, aged 4 to 14 years, with moderate to severe intrinsic asthma (IA) were studied. Symptom-Score charts were used to confirm the relationship of acute respiratory tract infections to exacerbations of asthma. Hypersensitivity to eight commonly occurring bacteria from the normal flora of the upper respiratory tract was studied by skin test, by crossed immunoelectrophoresis, and by basophil histamine release in vitro, using ultrasonicates of the bacteria as antigens. Skin tests were all negative. All children contained low titers of precipitating antibodies against most of the bacteria, but in this respect they did not differ from normal children. In contrast, release of histamine was induced in leukocytes from the IA children by all, or most sonicates, while such reactions, were less frequent in control children. The pattern of responses indicated an element of specificity. These was no correlation to precipitating antibodies, or to the microbial flora of the children. Positive responses were characterized by low values of maximal histamine release, and by a tendency to fluctuations with time. Because of these fluctuations, and because the IA children and control children were tested on separate occasions, we cannot be certain as to the real difference between these two groups. Our studies do, however, demonstrate that water-soluble constituents of all the bacterial strains tested were capable of causing the release of histamine in vitro, but that this phenomenon is not restricted to IA. The clinical significance of these findings awaits further investigations on the mechanism(s) of release in vitro by such agents.

Particle counting immunoassay (PACIA) of ferritin

Particle Counting ImmunoAssay (PACIA) has been adapted to the determination of serum ferritin. Polystyrene particles (0.8 micrometers) were coated with anti-ferritin antibodies and the concentration of ferritin determined by the agglutinating activity of this protein. The agglutination was measured by the reduction of the number of non-agglutinated particles counted in an optical blood cell counter. Non-specific agglutination and inhibition of agglutination were prevented in 99% of clinical samples by the use of F(ab')2 fragments of the antiserum IgG to coat the particles and by using slightly dissociating conditions (pH 9.2, ammonium thiocyanate, EDTA). The system was automated with a sampling rate of 50/h and an incubation time of 25 min. The standard curve ranged from 1 to 100 micrograms/l; recoveries were between 93.6 to 100.2%; the correlation coefficients of PACIA with radioimmunoassays calculated respectively on 99 and 91 samples were 0.974 and 0.984; maximal within- and between assay CV were 11.2% and 7.7%.

Immunoassay with stable polystyrene latex particles

Three variations of a new immunoassay which used physicochemically stable latex particles (LP) are described. New features include (1) separation of free and agglutinated LP by centrifugation after the addition of sucrose, and (2) combined use of two or three types of LP. Assay results for anti-rabbit IgG (anti-RG), human chorionic gonadotrophin (HCG), C3 components and insulin indicated excellence of these methods in sensitivity, reproducibility and preservability of reagents.

An automatic continuous flow method for the determination of antipolyamine antibodies in human sera

Latex particles with covalently bound polyamines were used to detect antipolyamine antibodies in human sera in manual and automated nephelometric assays. There was good correlation between the two assays though in the former aggregate size was measured after 24 h incubation whereas in the latter monomer loss was determined after 1 h.

Particle counting immunoassay. IV. The use of F(ab')2 fragments and N epsilon-chloroacetyl lysine N-carboxyanhydride for their coupling to polystyrene latex particles

Improved performance with the latex agglutination immunoassay, PACIA, is possible when the F(ab')2 fragments of antibody are chemically coupled at their hinge region to a protein-coated latex using a new coupling reagent, N epsilon-chloroacetyl lysine N-carboxyanhydride. This reagent, whether by orientating the complete antibody molecule or its F(ab')2 fragment or by preventing antibody denaturation, increased the sensitivity of the PACIA method. The use of F(ab')2 fragments eliminated most serum interference with the test.