Abstract
Objectives of the current work were to investigate the role of photoperiod and melatonin in the alteration of immune responses in a reptilian species. Animals were kept on a regimen of short or long days. Blood was obtained and leucocytes were isolated to study various innate immune responses. Lymphocytes were separated from blood by density gradient centrifugation and were used to study proliferation. Respiratory burst activity was measured through nitrobluetetrazolium reduction assay while nitric oxide production by leucocytes was assayed by nitrite assay. Lymphocytes were isolated and used to study proliferation with and without B and T cell mitogens. Photoperiodic manipulation acted differentially on leucocyte counts. Nitrite release was increased while superoxide production was decreased in cultures obtained from the snakes kept on the short day regimen. Significant enhancement of mitogen induced lymphocyte proliferation was observed in cultures from the animals kept in either long or short days compared to cultures from the animals kept in natural ambient day length. Use of in vitro melatonin showed that lymphocytes from the animals, kept in long days, were more reactive. Photoperiod induces changes in immune status which may permit adaptive functional responses in order to maintain seasonal energetic budgets of the animals. Physiological responses (like elevated immune status) are energetically expensive, therefore, animals have evolved a strategy to reduce immune functions at times when energy is invested in reproductive activities. Natrix piscator breeds from September to December and elevated pineal hormone in winter suppresses reproduction while immunity is stimulated.
Highlights
Objectives of the current work were to investigate the role of photoperiod and melatonin in the alteration of immune responses in a reptilian species
Total leucocytes decreased significantly in snakes subjected to short days in comparison with snakes maintained in natural day length (12L:12D) or long days (Fig. 1C)
Phagocytosis by leucocytes is concerned, the number of cells performing phagocytosis decreased significantly in the snakes kept in 08L:16D, there was no significant change in phagocytosis in animals kept in long days, when compared with control animals (Fig. 3C)
Summary
Objectives of the current work were to investigate the role of photoperiod and melatonin in the alteration of immune responses in a reptilian species. Oxidative stress in leucocytes, measured by reactive oxygen species (ROS) level and lymphocyte proliferation was found to be seasonal[23] In light of these studies, it may be that changes in the immune responses that occur in response to maintaining animals on short day regimens are likely to be directly or indirectly related to elevated melatonin secretion. According to the energy trade-off hypothesis, elevated melatonin level in winter suppresses gonadal function while immunity is e nhance[24] Most research in this field is focused on mammals and birds, the study of unconventional animal models still represent a useful approach to obtain an insight of how photoperiod mediated immune function has changed during the course of vertebrate evolution. Understanding the immunity and its interaction with seasonality has provided important insights in the evolution of this physiological process
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