Hassall's corpuscles: a measure of activity in the thymus during involution and reconstitution.

Areas occupied by Hassall's corpuscles were measured by planimetry of histological sections of guinea-pigs' thymus glands that had been involuted by one of three methods: (1) local X-irradiation of the thymus, or (2) restriction of food intake, or (3) systemic injections of cortisone. The corpuscular area increased two- to three-fold compared with control glands and this increase occurred before lobules began to shrink. Hassall's corpuscles hypertrophy simultaneously with diminution in width of the cortex, i.e. with lysis of thymocytes. Hence, it is argued that the area taken up by the corpuscles provides a measure of thymocyte destruction during involution. Moreover, since the corpuscles are markedly diminished during reconstitution, 3–4 weeks after X-irradiation, their size is a further reflection of cellular turnover in the thymus.