Effect of azathioprine on the affinity of antibodies against acetylcholine receptor: analysis with purified antibodies

Affinity chromatographic purification of antibody subsets depends on the mode of cross-linking of antigen to the affinity matrix

Affinity columns for the separation of rabbit antibodies (Abs) to the purified nicotinic acetylcholine receptor (AcChR) from Torpedo californica electroplax were constructed in two ways: (1) by direct cross-linking of purified AcChR to cyanogen bromide activated Sepharose 4B, and (2) by first cross-linking a purified curarimimetic neurotoxin to cyanogen bromide activated Sepharose 4B, subsequently saturating with AcChR, and finally cross-linking the toxin to noncovalently bound receptors with bisimidate cross-linkers such as dimethyl suberimidate (DMS). Ab(AcChR) from pooled rabbit antisera were chromatographed in near stoichiometric proportions to the AcChR bound to the column to allow equilibrium selection of antibodies directed against sites which were not sterically hindered. The concept that columns of the second type subfractionate Ab(AcChR) was tested by analyzing Ab(AcChR) from column fractions with an ELISA and radioimmunoassay (RIA) procedure. The ELISA was constructed to that the exposed face of the AcChR was the same as that expected for columns of the second type, i.e. for the internal or cytoplasmic face. Enhanced ratios of ELISA to RIA measures of Ab(AcChR) reflected substantial purification of cytoplasmic face antibodies in DMS-cross linked columns. Total Ab(AcChR) was measured by RIA. Both types of columns gave substantial purification of tightly bound antibodies, i.e. those which were eluted with 3M potassium thiocyanate. Thirty-fifty percent of the IgG eluted was found in these fractions, which contained 2-6% of the total eluted protein. Approximately half of the total IgG present in these fractions represented specific IgG against AcChR. Both types of columns could be reutilized giving similar results; however, their efficiency was diminished.

Computer simulation of plasma exchange therapy in autoimmune disease

Computer simulation of plasma exchange in autoimmune disease shows that a single treatment may reduce the amount of antibody bound to antigen by as much as 60-80%. The reduction is greatest when autoantibody is of low affinity and there is an excess of antibody compared to antigen.

Purification of anti-acetylcholine receptor antibody from patients with myasthenia gravis

The purification of specific anti-acetylcholine receptor antibodies from the plasma of 3 patients with myasthenia gravis was achieved by affinity chromatography using an immunoadsorbent of alpha-bungarotoxin-Sepharose 4B covalently linked to acetylcholine receptor extracted from human leg muscle. The specific antibody was eluted with potassium thiocyanate. The antibody characteristics were monitored throughout the purification procedure. The high avidity of the antibodies for the acetylcholine receptor was preserved but there was some loss of lambda light chain specific antibody.

Immune regulation of experimental myasthenia

Experimental autoimmune myasthenia gravis (EAMG) is an appropriate model for studying the molecular origin, immunological mechanism and regulation of myasthenia gravis. Several approaches are being utilised for the regulation of the immune response to AChR and for immunosuppression of EAMG: Corticosteriods and azathioprine can suppress EAMG concomitantly with suppression of immune responses to AChR. High dose cyclophosphamide treatment in mice facilitates the onset of EAMG and results in a selective suppression of the humoral response to AChR whereas the cellular response is enhanced. Specific immunosuppression of EAMG is achieved by using a nonmyasthenic, denatured AChR preparation which cross reacts with the intact receptor. Various degradations and modifications of AChR are being performed in order to identify the smallest molecular entity responsible for the myasthenic activity of AChR. Studies on specific monoclonal antibodies, anti-idiotypes, and on the effect of measles virus on EAMG are being described and their possible significance in regulating myasthenia are being discussed.