Properties of monoclonal antibodies to nicotinic acetylcholine receptor from chick muscle.

Four stable, hybrid-cell lines secreting monoclonal antibodies to distinct determinants on the nicotinic acetylcholine receptor from chick muscle have been established. These were characterised by the following criteria: immunoglobulin isotype, ability to produce experimental autoimmune myasthenia gravis in mice and reactivity towards homologous and heterologous acetylcholine receptor proteins. Two monoclonal antibodies were found to inhibit the reaction of alpha-bungarotoxin with homologous acetylcholine receptor; in addition one of these, on binding to receptor-toxin, induced a rapid dissociation of the complex (t1/2 = 0.5 h at 23 degrees C). Three of the antibody preparations recognised epitopes on this receptor from muscle of other species and two of these caused experimental autoimmune myasthenia gravis in BALB/c mice following passive transfer. The latter two recognised to significant extents the alpha-bungarotoxin binding component purified from chick optic lobe and brain cortex. Sedimentation analysis demonstrated that two of the monoclonal antibodies form a distinct size (s20, w = 12S) of complex with the receptor of chick muscle which most probably corresponds to a 1:1 attachment of antibody and receptor; this may involve cross-linking of two determinants within the same oligomer. A similar observation was made with the alpha-bungarotoxin binding component from optic lobe using one of the cross-reacting antibodies. Another monoclonal antibody was found to be capable of forming much heavier complexes with the receptor from chick muscle, these are thought to involve inter-molecular cross-linking of oligomers. The observed properties of these antibodies are discussed in relation to their myasthenogenicity and with reference to the extent of structural similarities between the peripheral nicotinic acetylcholine receptor and the alpha-bungarotoxin binding protein from brain.