Detection and distribution of alfa-naphthyl acetate esterase activity in thymocytes of normal, myasthenic thymus and thymoma. Histochemical and cytochemical study in relation to E-rosetting.

The extent and distribution of alfa-naphthyl acetate esterase (ANAE) activity in both normal thymuses and thymuses or thymomas from patients with myasthenia gravis were investigated by enzyme histochemistry. In all a closely similar distribution of ANAE activity was recognizable. ANAE positive thymic lymphocytes were distributed preferentially at the cortico-medullary junction and in the medulla. Their numbers at these sites were higher in myasthenic patients than in normal adults (P less than 0.001) and lowest in fetuses. The relative numbers of cells showing both ANAE activity and EN-rosette-forming capacity was lower in thymocytes than peripheral lymphocytes but was increasing higher in thymuses from fetal, adult and myasthenic patients and in thymomas. These findings are discussed in relation to the stage of maturity of thymocytes and the importance of intrathymic immunological challenge in the attainment of these cells of functional properties usually acquired in the periphery.