Undiminished regulatory T cells in the thymus of patients with myasthenia gravis

The thymus has been implicated as a possible site of origin that triggers autoimmunity in myasthenia gravis (MG). Although several groups have suggested that the decrease in the number of regulatory T (Treg) cells contributes to the onset of MG, the exact role of Treg cells in MG remains unclear. To address this point, we examined the number and distribution of Treg cells in a large number of patients with MG.

Immunohistofluorescence analysis of Foxp3 along with CD4 and CD8 was performed in thymic sections of MG (+) (n = 24) and MG (-) patients (n = 27). Circulating CD4(+)CD25(+) cells in the peripheral blood of patients with MG (n = 15) and age-matched healthy subjects (n = 15) were also analyzed.

Foxp3(+)CD4(+)CD8(-) cells were predominantly found in the thymic medulla and their number declined with age. There was no significant difference in the number or the distribution of Foxp3(+)CD4(+)CD8(-) cells in the thymus between MG (+) and MG (-) patients. The number of circulating CD4(+)CD25(+) cells in the peripheral blood of patients with MG was not significantly altered compared to that in healthy subjects.

The cellularity of Treg cells in the thymus and circulation is not diminished in patients with myasthenia gravis.