DARK RETICULAR EPITHELIAL-CELLS OF THYMUS AS PRIMARY TARGET OF HETEROLOGOUS ANTI-LYMPHOCYTE SERUM IN BALB-C MICE - ULTRASTRUCTURAL-STUDY CORRELATED WITH DATA ON THYMUS SUBSTITUTION

Effects of heterologous [rabbit] anti-lymphocyte serum (ALS) administration on the ultrastructure of the thymus were investigated in intact and adrenalectomized BALB/c mice. The alterations of dark reticular epithelial cells (DREC) were seen 1 h after serum administration to intact mice. A large portion of DREC disappeared from the thymus. Adrenalectomized mice showed basically the same ultrastructural pattern of alterations, their degree and incidence being lower than those of intact mice. The alterations of thymocytes occurred later than those of DREC. In parallel experiments with thymus substitution ALS-treated thymuses are not able to contribute to the overall recovery from ALS effects, when installed in thymectomized recipient mice. The recovery of normal DREC ultrastructure began in both experimental groups of animals at about 24 h after serum administration. DREC damage is provoked by several factors, 1 of which might be the direct action of ALS on DREC. A model of the structural and functional involvement of the thymus as a consequence of ALS administration is proposed.