Irrelevance of anti‑nAChR cytoplasmic loop antibody in the degree of myasthenia gravis.

Anti‑nicotinic acetylcholine receptor (nAChR) antibody in myasthenia gravis (MG) usually refers to that against the extracellular domain (ECD) of nAChR. However, growing evidence has indicated that there also exists the nAChR antibody against the nAChR cytoplasmic loop (CL) in patients with MG. Some studies have demonstrated that the anti‑CL antibody may play a protective role in animal models of experimental autoimmune MG. However, to date, limited or no information is available as to whether anti‑CL antibody plays a beneficial role in patients with MG. In this, we examined the levels of anti‑CL and anti‑ECD antibodies in the sera of 76 patients with MG from the MG sample bank of our department, including 29 generalized MG (gMG) and 47 ocular MG (OMG) cases, as well as 40 healthy controls by radioimmunoassay. We also analyzed the correlation between anti‑CL antibody levels and the degree of severity in patients with MG. Our results revealed that among the 76 patients with MG, 61 serum samples (80.3%) were positive for anti‑ECD nAChR antibody, among which 38 (38/61, 62.3%) were positive for anti‑CL antibody. The levels of anti‑ECD antibodies in gMG were higher than those in OMG; however, the levels of anti‑CL antibodies in gMG were comparable with those in OMG. No clear correlation was observed between the anti‑ECD antibody levels and those of anti‑CL antibody. Taken together, our findings provide the first clinical evidence of the possibly different role of anti‑CL antibody in patients with MG compared to its role in animal models of MG. Anti‑CL antibody may not exert a beneficial effect in patients with MG, but may play an as yet udetermined role in the development of MG.