Epitope analysis of AChR Ab in patients with myasthenia gravis using sensitive enzyme immunoassay

Cytotoxic T cell activity against peptides of Hu protein in anti-Hu syndrome

Half of all patients with limbic encephalitis and small cell lung carcinoma (SCLC) have anti-Hu antibodies that react with all of central and peripheral nervous system neuronal nuclei in immunohistochemical studies and 35- to 40-kDa reactive bands on western blots of extracts from isolated central nervous system neurons. The roles of anti-Hu antibodies in neuronal damage, however, have yet to be shown. Evidence of infiltration of CD8-positive T cells to tumors and affected nervous tissues and limited use of the T cell receptor repertoire in the central nervous system suggests that CD8-positive cytotoxic T cells (CTL) cause neuronal loss. We found the HLA B7 supertype in all of seven Japanese patients with anti-Hu syndrome. We identified HLA class I-restricted, CD 8-positive cytotoxic T cell activity in peripheral blood from three patients with anti-Hu syndrome for five peptides with binding motifs for the HLA B7 supertype in the amino acid sequence of the Hu protein. This study support the involvement of CD8-positive cytotoxic T cells in the development of paraneoplastic neurological syndrome with anti-Hu antibodies.

Detection of antibodies directed against the cytoplasmic region of the human acetylcholine receptor in sera from myasthenia gravis patients

The nicotinic acetylcholine receptor (AChR) is the autoantigen in the human autoimmune disease myasthenia gravis (MG). Anti-AChR antibodies in MG sera bind mainly to conformational epitopes, therefore the determination of their specificities requires the use of native AChR. Antibody competition studies suggest that most MG antibodies are directed against the extracellular part of the molecule, whereas antibodies directed against the cytoplasmic region of the AChR have not been detected. To determine whether even small quantities of such antibodies exist in MG sera, we performed competition experiments based on the inhibition by MG sera of the binding of MoAbs to the human AChR, rather than inhibition by MoAbs of the binding of MG sera performed earlier. When MoAbs directed against cytoplasmic epitopes on the alpha or beta subunits (alpha 373-380 and beta 354-360) were used as test MoAbs, 17% or 9% of MG sera inhibited the binding of the anti-alpha or anti-beta subunit MoAbs, respectively, by > or = 50%. Non-specific inhibition was excluded. These results suggest the presence, in several MG sera, of antibodies directed against cytoplasmic regions of the AChR; yet these antibodies seemed to represent a relatively small proportion of the total anti-AChR antibodies. The corresponding epitopes may be involved in the inducing mechanisms in certain MG cases, and knowledge of the presence of such antibodies may be useful in understanding the autoimmune mechanism involved in MG.