Interdigitating cells are resistant cells against radiation-induced-apoptosis

The periarteriolar lymphoid sheath (PALS) of rat spleen, which was selectively 60Co-irradiated, was examined using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and transmission electron microscopy. Immediately after irradiation, lymphocytes in the PALS showed apoptosis, Apoptotic lymphocytes in the PALS showed apoptosis. Apoptotic lymphocytes were phagocytized by macrophages. From 1 day after irradiation, the number of intact T lymphocytes increased. The PALS recovered to the control level at day 4. The cytoplasmic extensions of interdigitating cells (IDCs) were reduced and less interdigitated with extensions of neighboring IDCs. The morphology of cytoplasmic extensions of IDCs got recovering from the 4th day after irradiation, and the interdigitation of cytoplasmic extensions recovered completely 11 days after irradiation. No apoptosis occurred in IDCs. The IDCs were radiation-induced apoptosis-resistant. Their morphological changes seemed to be related to the surrounding microenvironmental changes. (author)