Comparison of Fas expression in thymocytes from controls and MG patients. Freshly isolated thymocytes were stained with anti-Fas antibody, then with goat-antimouse IgG antibody, and finally with Cy-chrome-labeled streptavidin. Using the Lysis II program, a marker was set to define the proportion of Fas^hi thymocytes. (A) Representative analysis of one control and three MG thymuses. The percentage of Fas^hi thymocytes is indicated, as well as age and the anti-AChR antibody titer (nmol/L). Fas expression is clearly increased in patients with positive anti-AChR antibody titers (MG2 and MG3) but not in the patient with a negative titer (MG1). (B) The proportion of Fas^hi thymocytes was determined in 26 MG patients and 7 control subjects. Two groups of patients (anti-AChR antibody titer < 1 nmol/L and ≥1 nmol/L) are distinguished and compared with controls by using the Mann-Whitney test. The bar represents the mean value. Only the group of patients with positive anti-AChR antibody titers differed from the controls.