Myasthenic CD4⁺CD25⁺ thymocytes are responsive to mitogenic stimulation and their suppressive activity is impaired. (A) CD8-depleted thymocytes were purified by positive selection of CD4⁺ cells followed by positive or negative selection for CD25 expression using MACS magnetic microbeads. A representative experiment using newborn and myasthenic thymocytes is shown. (B) CD4⁺CD25⁺ thymocytes from 5 controls and 3 patients with MG were stimulated in the presence of irradiated allogenic T cell–depleted PBMCs and 5 μg/mL PHA. The results are expressed as the percent of proliferative response of CD4⁺CD25^- thymocytes, with proliferation in the absence of CD4⁺CD25⁺ cells corresponding to 100%. Mean values (± SD) of triplicate wells are reported. (C) The CD4⁺CD25^- thymocytes were stimulated in the presence of different doses of CD4⁺CD25⁺ thymocytes. Mean values (± SD) of 3 separate experiments are shown.