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Effects of melatonin on macrophages/microglia in postnatal rat brain
1Department of Anatomy, Faculty of Medicine, National University of Singapore, Singapore. antkaurc@nus.edu.sg
Abstract:
The present study examined the response of macrophages/microglia to multiple injections of melatonin in the pineal gland and different regions of the brain. The macrophages/microglia showed a significant increase in cell numbers and upregulation of complement type 3 receptors (CR3), major histocompatibility complex class I (MHC I) and class II (MHC II) antigens, and antigens of monocyte/macrophage lineage, as detected by the antibodies OX-42, OX-18, OX-6, and ED1, respectively. The upregulation of the above antigens was observed in 1-d-old rats given daily injections of melatonin and killed at 7-11 d of age; no noticeable change was observed at earlier time intervals. The macrophages/microglia expressing the above antigens appeared round and showed a vacuolated cytoplasm compared with ramified cells in the control rats. Upregulation of CD4 antigens as detected with the antibody W3/25 was also observed in macrophages/microglia in the corpus callosum and epiplexus cells in the lateral ventricles, but not in the pineal gland and the cerebral cortex in the same age group. In rats killed between 2 and 5 d, and at 14 d of age after melatonin treatment, the immunoreactivities of macrophages/microglia with the above mentioned antibodies were comparable to cells in the control rats. Immunoreactive cells were not detected in any of the age groups in melatonin-treated or control rats with the antibodies W3/13 and OX-33, which are markers for T and B lymphocytes. It is concluded that CR3 receptors, MHC antigens, and CD4 antigens on macrophages/microglia are upregulated following melatonin administration. On the other hand, once the melatonin treatment is discontinued the expression of the various antigens/receptors returns to normal levels, suggesting that increased immune potentiality and its maintenance in these cells require the continuous action of the drug.
Insights
Melatonin injections increase immune cell markers (CR3, MHC I/II, CD4) in young rats
Area of Science:
- Neuroimmunology
- Endocrinology
Background:
- Macrophages and microglia are key immune cells in the central nervous system.
- Melatonin is a hormone with known immunomodulatory effects.
Purpose of the Study:
- To investigate the impact of melatonin administration on macrophages and microglia in the brain.
- To assess changes in immune cell markers following melatonin treatment in developing rats.
Main Methods:
- Rats received daily melatonin injections from 1 day of age.
- Immunohistochemistry was used to detect macrophage/microglia markers (CR3, MHC I/II, CD4) via antibodies (OX-42, OX-18, OX-6, ED1, W3/25).
- Analysis was performed at various time points (7-11 days, 2-5 days, 14 days) post-treatment.
Main Results:
- Melatonin treatment led to increased macrophage/microglia numbers and upregulation of CR3, MHC I/II, and CD4 antigens in specific brain regions.
- Upregulation was observed in rats aged 7-11 days, with cells appearing round and vacuolated.
- Immune marker expression returned to normal levels after melatonin treatment cessation.
Conclusions:
- Melatonin administration transiently enhances the immune potential of macrophages/microglia in developing rat brains.
- Continuous melatonin exposure is required for sustained upregulation of these immune markers.
- T and B lymphocyte markers were not detected, indicating a specific effect on myeloid lineage cells.