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Summary Cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4) is an important molecule in the down‐regulation of T‐cell activation. A study was undertaken to evaluate the association of the CTLA‐4 gene polymorphisms −319C/T, +49A/G, (AT)n, CT60A/G and Jo31G/T with the levels of membrane CTLA‐4 (mCTLA‐4) and cytoplasmic CTLA‐4 (cCTLA‐4) in CD4+ T lymphocytes from patients with multiple sclerosis (MS) and with susceptibility to MS, and the course of the disease. It was found that the Jo31GG and CT60GG genotypes were associated with decreased mean fluorescence intensity (MFI) of total CTLA‐4 (mCTLA‐4 + cCTLA‐4) molecules in CD4+ T cells from both relapsing‐remitting (RR) and secondary progressive (SP) MS patients compared with others. Consequently, possessing the Jo31G allele and/or the CT60G allele were associated with susceptibility to MS. The percentages of cells expressing mCTLA‐4 and cCTLA‐4 in RR patients were higher in carriers of the alleles non‐predisposing to MS (namely CT60A and Jo31T), but the percentages of corresponding cells were unexpectedly significantly lower in SP patients than in RR patients. Increased risk of paresthesia and pyramidal signs as a first manifestation of disease, and earlier transition to the SP form in those patients, was also noted. It is hypothesized that the decreasing frequencies of cells expressing immunosuppressive mCTLA‐4 and cCTLA‐4 in carriers of alleles non‐predisposing to MS (i.e. CT60A and Jo31T) may lead to inadequate down‐regulation of ongoing T‐cell responses in these patients and, as a consequence, earlier progression of disease from the RR form to the SP form.

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