Figure 3.

Measurement of antibody-AChR complexes and rapsyn-AChR aggregates by radioimmunoassay. AChR clustering by rapsyn was tested by adding a limited amount of anti-rat AChR antibody to membrane extracts of untreated and rapsyn-treated control muscles. A: Hypothetical scheme of AChR complexes, showing precipitation of AChR-rapsyn clusters by a limited amount of anti-AChR antibodies. Cross-linking of receptors by rapsyn (n) would lead to the co-precipitation of a larger amount of radioactive α-BT. If clustering by rapsyn is absent, more AChR remains in solution. B: Rapsyn transfection did not lead to increased size of rapsyn-AChR aggregates in membrane extracts of control muscles (control +AChR antibodies); cross-linking of AChR by rapsyn as shown in A did not occur. In EAMG muscles, rapsyn transfection resulted in increased in vivo binding of antibodies to AChR in EAMG animals (B, EAMG + normal rat serum).