Mitotic activity and cell degeneration in the mouse thymus over a period of 24 hrs

Circadian rhythm-related genes: implication in autoimmunity and type 1 diabetes

Recent gene association and functional studies have proven the implication of several circadian rhythm-related genes in diabetes. Diabetes has been related to variation in central circadian regulation and peripheral oscillation. Different transcriptional regulators have been identified. Circadian genes are clearly implicated in metabolic pathways, pancreatic function and in type 2 diabetes. Much less evidence has been shown for the link between circadian regulation and type 1 diabetes. The hypothesis that circadian genes are involved in type 1 diabetes is reinforced by findings that the immune system undergoes circadian variation and that several autoimmune diseases are associated with circadian genes. Recent findings in the non-obese diabetic mouse model pinpoint to specific mechanisms controlling type 1 diabetes by the clock-related gene Arntl2 in the immune system.

When should the immune clock be reset? From circadian pharmacodynamics to temporally optimized drug delivery

Immune defenses are organized along both 24-h and yearly time scales. Two circadian systems have been isolated in man, which can be desynchronized: (1) the circulation of T, B, or NK lymphocyte subsets in peripheral blood and (2) the density of epitope molecules (CD3, CD4, ...) at their surface, which may relate to cell reactivity to antigen exposure. The in vitro response of murine splenocytes to interleukin 2, interferon (IFN), or cyclosporin A strongly depended upon circadian time of exposure. Temporally optimized delivery of biologic response modifiers (BRM) may be guided by immunologic marker rhythms. An alternative yet complementary strategy was sought with IFN: since high doses were shown as more effective than low doses against several malignancies, this drug was given at the presumed less toxic time, so that its dose could be increased. Continuous drug delivery was circadian modulated in 8 cancer patients. Dose intensities twice to fourfold higher than those usually recommended were safely infused to ambulatory patients. Chronotherapy with BRM may represent a necessary step for optimizing the immunologic control of malignancies.

DNA-synthesis in the rat thymus after focal thermolesions on abdominal organs

The changes in the DNA-synthesis of lymphocytes in the different zones of the rat thymus were autoradiographically studied with 3H-thymidine after focal thermonecroses (740 degrees C/4 sec) on abdominal organs and sham operation (laparotomy). A single thermolesion was performed in separate groups of rats on the liver and spleen, whereas a third group received multiple heat lesions (liver, kidney, stomach wall). A slight decrease of the labeling index occured during the first 36 h after the sham operation and was attributed to an unspecific stress effect leading to an increased release of corticosterones. The most remarkable and contrasting result was the observation that after thermonecroses a decrease of the labeling index of thymus-lymphocytes did not happen during the first 48 h but rather a marked increased with a maximum on the fifth day. It was concluded that the stimulated DNA-synthesis in the thymus might be related to a cell mediated immune response against thermocoagulated tissue components or to an immediate T-cell dysfunction, which is known to develop after burns. In both cases the thymus might react with an increased division and maturation of lymphocytes regulated through a feed-back mechanism.

Studies on the regulation of lymphocyte production in the murine thymus and some effects of a crude thymus extract

Cell proliferation in the murine thymus was studied in vivo under normal conditions and from 0 to 24 hr after a single injection of a water-soluble extract from mouse thymus, mouse spleen, and mouse skin. The thymus extract reduced during the first 24 hr the mitiotic activity 40%; the spleen extract had a weaker inhibitory effect. The skin extract had no such effect. The thymus extract and spleen extract inhibited the flux of cells into the S phase 0-8 hr after the injection of the extract. Initial labelling index was also reduced in this period. Eight hours after injection of the thymus or spleen extracts the inhibited cells initiated DNA synthesis. The rate of progression of blast cells through the cell cycle was normal 24 hr after the injection of the extracts. It was deduced from the analysis that the thymus extract inhibits processes triggering G0/G1 cells into DNA synthesis, the inhibition of G2 efflux being of minor importance. Finally a model for the regulation of proliferating thymic blast cells and the emigration of small lymphocytes from the thymus is proposed.