The affinity of soluble immune complexes for concanavalin A

Determination of the immunoglobulin class of complement-dependent cytotoxic antibodies in serum of D23 hepatoma-bearing rats

The immunoglobulin class of the complement-dependent cytotoxic antibodies in serum from D23 hepatoma-bearing rats (D23 TBS) for D23 hepatoma cells was analysed. When studied by affinity chromatography with concanavalin A, protamine, or staphylococcal protein A conjugated to Sepharose, the cytotoxic activity bound to the former two but not protein A. The binding fractions were further characterized by column chromatography on Sepharose CL-4B. The cytotoxic activity was recovered exclusively in the high molecular weight fractions corresponding to human IgM. Monitoring with IgG- or IgM-specific rabbit antibodies indicated that these high molecular weight cytotoxic fractions contained both IgG and IgM. However, fractionation of D23 TBS at low pH suggested that cytotoxicity was due to IgM antibodies rather than to immune-complexed IgG antibodies. This was supported by the findings that rabbit antirat IgM antibodies inhibited the cytotoxicity of TBS completely when added at high dilutions.

Binding of dog immunoglobulins G, A, M, and E to concanavalin A

The binding of dog immunoglobulins G, A, M and E to concanavalin A (Con A) has been investigated. A passive cutaneous anaphylaxis test was used for measurement of dog IgE, and enzyme-linked immunosorbent assay was used for measurement of dog IgG, IgA and IgM. After the dog serum fraction was applied to a Con A-Sepharose column, sequential elution with different buffers was performed; 100% of IgE and IgM, 60% of IgG and 58% of IgA bound to the Con A-Sepharose. IgE was eluted by mannose, methylglucose, and methylmannoside. IgG was eluted by glucose, mannose, methylglucose, and methylmannoside. IgA and IgM were eluted by methylmannoside only. This provides a useful technique in the purification of dog immunoglobulins, especially dog IgE.

Importance of the IgG isotype, not the state of glycosylation, in determining human rheumatoid factor binding

We investigated the influence of carbohydrate on the binding of human rheumatoid factors (RF) to the Fc fragment of IgG. The monoclonal RF studied were derived from the serum of patients with mixed cryoglobulinemia or from hybridomas generated from patients with rheumatoid arthritis (RA) and systemic lupus erythematosus. Polyclonal RF were derived from patients with RA. The carbohydrate located on the Fc fragment, regardless of whether it contained different amounts of mannose or reduced amounts of galactose, or was removed, did not affect the binding of the RF. In contrast, the isotype of the Fc was found to be critical. Two groups of hybridoma RF could be delineated. One group bound preferentially to IgG1 and/or IgG2, and a second group (primarily from patients with RA) bound preferentially to IgG3 and/or IgG4. Our results indicate that the isotype of the Fc fragment, and not the extent of galactosylation, influences the binding of the RF.

Flow-cytometric detection of circulating immune complexes

In an effort to develop an assay which would rapidly detect and analyze circulating immune complexes, we have adapted the Raji cell radioimmunoassay (RIA) to a flow cytometric (FCM) analysis. The advantages of immune complex analysis by FCM are many. Foremost is the effectiveness and efficiency of the FCM method relative to the radioimmunoassay (RIA) method. The data demonstrated that FCM detection is three times more sensitive than RIA detection. Only populations of viable Raji cells bearing immune complexes are analyzed because parameters of the FCM analysis permitted the elimination (gating out) of dead cells. The determinations are rapid and the data are immediately available for several additional analyses. Because of the availability of many fluorescent monoclonal antibodies to complement components, viral antigens, light chains and immunoglobulin isotypes, it is possible to detect many components that might be present in the Raji cell bound complexes. Finally, the Raji cells can be characterized in different stages of their cell cycle to generate information about the state of the cells and the density of the receptors involved in binding the complexes.

Preparative isolation of immune complexes from serum by sucrose gradient ultracentrifugation

Immune complexes were isolated by ultracentrifugation in sucrose gradients (20-65% (w/w]. the centrifugation procedure was demonstrated to be isopycnic. The banding density of the complexes was influenced by the chemical nature and molecular size of the antigen and by the antigen to antibody ratio. The method was applied for preparative isolation of immune complexes from patients with systemic lupus erythematosus, rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, and uncomplicated psoriasis.

Isolation of a rabbit IgG fraction with cytophilic properties

About 15% of rabbit IgG loaded on a column of Con A-Sepharose 4B was found to be specifically bound to the column due to a structural variation in its carbohydrate moiety. The Con A-retained rabbit IgG contained a higher amount of neutral hexoses than the initial IgG but its molecular weight, antigenic structure and half-life were identical or similar. The Con A-retained rabbit IgG has an affinity for the Fc receptor-bearing homologous macrophages which is 10 times higher than that of the initial IgG. The IgG fraction not retained on Con A-Sepharose is practically devoid of binding ability. These results suggest that the Con A-bound IgG may represent the cytophilic fraction of monomeric IgG responsible for the binding of IgG to Fc receptor-bearing cells.

Three step purification of C1q by DNA precipitation, ion exchange and lectin affinity chromatography

The difficulties associated with the isolation of pure C1q in sufficient amounts are reflected by the substantial number of isolation procedures, which are being published. The two major problems are a low yield and contaminating immunoglobulins. In addition, some isolation protocols appear to produce C1q contaminated with an inhibitor (C1q-INH). The present isolation protocol involves precipitation of C1q by DNA, chromatography using Sephadex QAE A 50 followed by Con A affinity chromatography. By this combination of purification steps maximal advantage was taken of the cationic properties and high carbohydrate content of the C1q molecule. The yield was 1-2 mg C1q per 100 ml serum. The isolated C1q was free of any demonstrable contaminants as demonstrated by Ouchterlony double diffusion and polyacrylamide gel electrophoresis.

Reactivity with patient antibodies of partially purified gp40 antigen from immune complexes in Burkitt's lymphoma and nasopharyngeal carcinoma

A glycoprotein antigen (gp40) was previously identified as a major component of immune complexes isolated from sera of patients with Burkitt's lymphoma (BL) and nasopharyngeal carcinoma (NPC). In the present work gp40 was partially purified from a pool of BL/NPC sera. Sera of patients with BL and NPC as well as sera of patients with other malignant and non-malignant diseases were tested for antibodies against gp40, using a double antibody radioimmunoassay. Practically all normal sera and sera of patients with non-malignant diseases had antibodies capable of binding radioiodinated gp40. In contrast, sera of patients with BL or NPC had very low binding, while sera of patients with other malignant diseases had intermediate binding values. The low binding activity of BL/NPC sera was shown to be due to inhibition by excess gp40 present in such sera. Effusions of patients with breast or ovarian cancer also contained demonstrable amounts of gp40. The origin of gp40 is still unknown.

Two large virion envelope glycoproteins mediate Epstein-Barr virus binding to receptor-positive cells

The four major Epstein-Barr virion envelope components were separated by column chromatography and reconstituted into artificial liposomes. These liposomes were tested for their ability to bind selectively to Epstein-Barr virus receptor-positive cells. Only when the two high-molecular-weight glycoproteins, VE1 and VE2, were present together was a stable binding complex formed. The addition of the other virion envelope components did not increase the levels of binding. This binding was inhibited by unlabeled viable virions and by neutralizing antisera, which recognized the two components. Adsorption of viable virus was also eliminated by the antisera. The enzyme susceptibility pattern of the cell-liposome interaction is similar to that of the virus-cell interaction, thus confirming the specificity of the binding site. A model for Epstein-Barr virus binding in which VE1 and VE2 coordinately recognize the same binding site is presented.

In vitro characterization of synthesized thyroglobulin immune complexes (IC). A model for studies of IC containing an autoantigen

Human thyroglobulin (Tg) immune complexes (TgIC) were preformed at different ratios from purified Tg, and Tg antibodies (TgAb) obtained from six patients with autoimmune thyroid diseases. TgIC were characterized by precipitation with polyethylene glycol, and sedimentation in sucrose gradient. TgIC from one patient were further characterized by concanavalin A (con A), and binding to the complement factor Clq and rheumatoid factor (RF). Tg and TgIC had almost identical binding to con A, no binding to Clq, but could be partially separated by ultracentrifugation and polyethylene glycol. The highest degree of separation was obtained by a RF-coated plastic tube radiometric assay, using 125-I-rabbit TgAb as indicator. Tg showed no binding to RF, and a dose-response curve of TgIC in serum could be established. There was a dependence of the Tg-TgAb ratio, TgIC at equilibrium and in antibody excess being detected most efficiently. The method may serve as an aid in the evaluation of the fate of Tg, TgAb and TgIC following thyroid damage (surgery, radioiodine) and may be extended as a model system in the investigation of immune complexes in connection with autoimmune disorders.

Multiple forms of anti-acetylcholine receptor antibody in myasthenia gravis

Sera of patients with myasthenia gravis (MG) contain anti-acetylcholine receptor (AChR) IgG antibodies (Ab) which have different antigenic specificities. Three Ab types were detected: (1) MG-I, which forms immune complexes with AChR; (2) MG-C, which decreases binding of AChR to concanavalin A; and MG-B, which blocks alpha-bungarotoxin binding to AChR. Sera from 152 MG patients were screened for the Ab types. Sixty-one percent contained MG-I, 26% contained MG-C, 10% contained MG-B, and 5% contained both MG-C and MG-B. The latter Ab types were associated with more severe forms of MG but showed no other clinical correlations. IgG antibodies of defined type were purified, and their interaction with unlabeled and toxin-prelabeled AChR from denervated rat muscle was studied in detail. Receptors are homogeneous with respect to determinants recognized by MG-I, but heterogeneous with respect to determinants recognized by MG-C (3 subpopulations, 22%, 28%, and 50% of AChR) and by MG-B (2 subpopulations, 30% and 70% of AChR). The stoichiometry of AChR interaction with the antibodies indicates that for each toxin-binding site, the receptor is divalent as an antigen for MG-I and MG-C but is tetravalent for MG-B. Denervated muscle AChR appears to be a mixture of at least 3 molecular forms of AChR, each of which has distinct immunological features as well as components common to all the receptor subpopulations.