MORPHOLOGICAL AND FLOW CYTOFLUOROMETRICAL ANALYSES OF REGENERATED RATTHYMUS AFTER IRRADIATION

Reconstituted rat thymuses were studied by immunohistochemistry, trans mission electron microscopy (TEM) and flow cytofluorometry on days 0, 1, 2, 3, 5, and 7 after whole-body sublethal irradiation (6 Gy). One d ay after irradiation, numerous apoptotic cells were seen in the cortic al thymus; the percentage of the sub-G1 peak representing apoptotic ce lls was 8.9% in the DNA content histogram of cytofluorometry. On day 3 , the thymic structure had been destroyed and no distinction was drawn between the cortex and medulla. In this stage, few thymocytes but man y macrophages were present, and the percentage of the sub-G1 peak reac hed a peak at 13.0%. Bromodeoxyuridine (BrdU) incorporated cells gradu ally increased after irradiation, and immunohistochemically numerous a poptotic cells were found primarily in the cortex on day 7. These thym ocytes showed some levels of electron density of the nucleus as reveal ed by TEM. The percentage of S phase cells did not change markedly (20 -30%) based on one-color DNA content histograms, but the percentage of early S and S phase cells was extremely high on day cells may result in apoptosis. The combination of immunohistochemistry, TEM and dow cyt ofluorometry to analyze DNA content and BrdU incorporation proved a us eful tool for investigating the reconstituted thymus.