Immunochemical characterization of interactions between circulating autologous immunoglobulin G and normal human erythrocyte membrane proteins

Identification of the Antigen Content of Electroimmunoprecipitates

Polyclonal antibodies including purified antibody fractions and animal or human antisera may react with unknown antigens or antigens other than their main specificity in reactions that are best visualized by gel electroimmunoprecipitation methods (e.g., when analyzing complex antigen mixtures). The great advantage of gel immunoprecipitation approaches is that each immunoprecipitate contains antigen in a pure form and that the precipitate is separated by position, shape, and size from other precipitates in the complex patterns of crossed immunoelectrophoresis. The identification of the antigen content of such immunoprecipitates is important but challenging because of the very stable, high-affinity complex formation leading to precipitation in the gels. Here, we present detailed step-by-step recipes for identifying the antigen content of electroimmunoprecipitates.

Identification of the antigen content of electroimmunoprecipitates

Polyclonal antibodies including purified antibody fractions and animal or human antisera may react with unknown antigens or antigens other than their main specificity in reactions that are best visualized by gel electroimmunoprecipitation methods, e.g., when analyzing complex antigen mixtures. The great advantage of gel immunoprecipitation approaches is that each immunoprecipitate contains antigen in a pure form and that the precipitate is separated by position, shape, and size from other precipitates in the complex patterns of crossed immunoelectrophoresis. The identification of the antigen content of such immunoprecipitates is important but challenging because of the very stable, high affinity complex formation leading to precipitation in the gels. Here, we present detailed step-by-step recipes for identifying the antigen content of electroimmunoprecipitates.

Capillary electrophoresis for the study of affinity interactions

Molecular recognition may be characterized both qualitatively and quantitatively by electrophoretic methods if complexed molecules differ in electrophoretic mobility from unbound ones. The use of capillary zone electrophoresis (CE) for the characterization of affinity interactions is advantageous because of the high resolution, reproducibility and wide applicability of the technique and because of the mild conditions, i.e., physiological buffers without additions of organics or detergents, that are often sufficient for highly efficient separations. CE gives the ability to characterize binding between small amounts of unlabelled reactants in solution, has few requirements for special characteristics of the interacting molecules and is also applicable to the study of interactions of individual components in mixtures, as detection of binding and analytical separation are achieved in one step. This is unique compared with other techniques for the study of non-covalent interactions. The advantages and disadvantages of using CE to demonstrate molecular interactions, to screen for specific ligand binding in complex mixtures and to calculate binding constants will be discussed.

Accelerated elimination from the circulation of homologous aged red blood cells in rats bearing anti-spectrin antibodies

In order to analyse a possible role of anti-spectrin antibodies in the clearance of aged red blood cells (RBC), a homologous system was employed, whereby a population of aged RBC, obtained by hypertransfusion, was injected into rats bearing a high level of anti-spectrin antibodies, following immunization with spectrin. The aged RBC bound the anti-spectrin antibodies 'in vitro' and were eliminated from circulation in spectrin-treated rats at a faster rate than in control rats with naturally occurring antibodies. The analysis of the clearance curves revealed aged RBC of heterogeneous lifespans: two principal populations of short- and longer-living could be identified. In rats with anti-spectrin antibodies, the survival of the short-living population was further reduced. However, the similar kinetics of elimination of aged RBC in the two groups (with naturally-occurring and induced antibodies, respectively) suggest that anti-spectrin antibodies strengthened the intervention of the naturally-occurring ones. On the basis of these results, we assume that during their aging in circulation, RBC can accumulate surface alterations to make spectrin accessible to antibodies so that, in addition to anti-band 3 antibodies, anti-spectrin antibodies may contribute to their elimination.

Changes in peripheral blood CD5 (Bla) B-cell populations and autoantibodies following blood transfusion

BACKGROUND

CD5 B cells and the natural autoantibodies they produce play a role in antigen presentation, tolerance induction, and maintenance of an idiotypic immune network. The effects of transfusion on autoantibodies and peripheral blood CD5 B cells were studied.

STUDY DESIGN AND METHODS

Eight previously transfused patients with sickle cell anemia and five patients who underwent orthopedic surgical procedures with transfusion were enrolled in the study. Patients in both groups received 1 to 2 units of allogeneic packed red cells. Ten untransfused healthy adults and five patients who underwent orthopedic surgery without transfusion were enrolled as controls. Peripheral blood CD5 B cells, serum levels of IgM, antinuclear antibodies, rheumatoid factor, and anticardiolipin IgM were quantitated either at the beginning of the study (baseline sample), before transfusion, or before surgery and either at 1-, 2-, 4-, 6-, and 8-week intervals after transfusion, after surgery, or after the baseline sample was obtained.

RESULTS

IgM levels and the absolute number of B cells that coexpressed CD5 rose to twice pretransfusion levels in six of eight transfused sickle cell anemia patients and in four of five transfused orthopedic surgery patients. No comparable increases in CD5 B cells were noted in untransfused controls. Preexisting rheumatoid factor and antinuclear antibody levels increased in four of five transfused orthopedic surgery patients. One sickle cell anemia patient developed anti-Fya despite receiving Fya-negative blood. Increasing titers of anti-Fya paralleled the increases in IgM and CD5 B cells after transfusion. One patient who developed a positive direct antiglobulin test after transfusion had large increases in serum anticardiolipin IgM. Anticardiolipin IgM was subsequently eluted from direct antiglobulin test-positive red cells obtained after transfusion. Antibodies with anti-Fya-like activity and anticardiolipin IgM were produced in vitro by CD5 B cells and not by conventional CD5-negative B cells.

CONCLUSION

An association was found between transfusion-induced increases in CD5 B cells and increased autoantibody production. These data may have implications for immunologic intervention to prevent the induction of red cell antibodies and other changes in the immune system caused by exposure to foreign antigens via blood transfusion.

Red cell-reactive non-specific immunoglobulins and autoantibodies in the sera of normal and anaemic dogs

The levels of red blood cell (RBC) membrane-reactive IgG were measured in sera from normal and anaemic dogs using an enzyme-linked immunosorbent assay with erythrocyte ghosts as the target antigen (g-ELISA). The anaemic dogs were classified as cases of primary autoimmune haemolytic anaemia (AIHA), other anaemias with elevated levels of RBC-bound immunoglobulin detected by a direct enzyme-linked antiglobulin test (DELAT), or DELAT-negative anaemias. The g-ELISA detected IgG capable of binding RBC membranes in all the serum samples tested, and the levels were significantly higher (P < 0.05) in dogs with AIHA than in cases of DELAT-negative anaemia or in healthy animals. When sera were preabsorbed with RBC ghosts, g-ELISA readings were reduced in two of three AIHA cases that were tested, but not in dogs from any other group. There was no correlation between g-ELISA results and serum IgG levels in the cases of AIHA, but there was a significant relationship (rs = 0.74, P < 0.001) between these parameters in the dogs with other DELAT-positive anaemias. When spectrin(s) from the internal RBC membrane skeleton was used as the target antigen in the s-ELISA, sera from all groups of anaemic dogs yielded a wide range of values. Although the levels of spectrin-reactive IgG were significantly higher (P < 0.05) in AIHA cases than normal dogs, suggesting that haemolysis provoked production of anti-membrane skeleton antibodies, the highest reading was recorded in a healthy animal. It is concluded that all canine sera contain IgG non-specifically reactive with RBC membranes and that serum antibodies against the erythrocyte surface can also be detected in some dogs with primary AIHA. Distinct spectrin-reactive serum IgG antibodies can also be demonstrated in normal and AIHA positive dogs.

Identification of autoantigens in autoimmune haemolytic anaemia by a non-radioisotope immunoprecipitation method

In human autoimmune anaemia (AIHA), warm autoantibodies frequently appear to have serological specificity for the Rh complex, but to date, immunochemical techniques have failed to demonstrate that the antibodies react with Rh-associated polypeptides. We describe the immunoprecipitation of red blood cell (RBC) autoantigens, using biotin labelling and a luminescent detection method. In three cases of warm AIHA, a band of 32 kD and a diffuse zone of 38-51 kD or 40-51 kD were specifically precipitated by eluted RBC autoantibody. This pattern corresponds closely with that precipitated by two Rh-specific monoclonal antibodies, BRIC 207 and AB5. Antibody from the three eluates also showed serological specificity for the Rh complex in a haemagglutination assay against a panel of RBC with a range of Rh phenotypes, including rare -D-/-D- and Rh null cells. Eluted autoantibody from another warm AIHA patient immunoprecipitated a peptide of 67 kD that did not correspond in apparent molecular mass either with Rh-associated bands, or with major RBC membrane proteins or sialoglycoproteins (SGP). The haemagglutination assay showed that this eluate contained both Rh-specific and Rh-unrelated antibody. Warm autoantibody eluted from the RBC of a clinically normal, but direct antiglobulin test positive, blood donor was serologically unreactive with the Rh complex, and immunoprecipitated unknown peptides of 26, 29, 35, 48 and 51 kD, together with a band of 90 kD that comigrated with SGP alpha 2 (glycophorin A). In six further warm AIHA cases, no antigens were precipitated by autoantibody-containing RBC eluates. Overall, the results demonstrate that autoantibodies bind to Rh polypeptides in some, but not all, patients with warm AIHA, suggesting that the aetiology of the disease may vary.