|Title||Seasonal changes in immune function|
|Author||R.J. Nelson and G.E. Demas|
|Publication||Quarterly Review of Biology|
|Issue||Volume 71 Number 4|
|Keywords||inhibition, reproduction, immune system function, seasonal, short days, mammals, animals, photoperio|
|Winter is energetically demanding. Physiological and behavioural adaptations have evolved among nontropical animals to cope with winter because thermoregulatory demands increase when food availability decreases. Seasonal breeding is central within the suite of winter adaptations among small animals. Presumably, reproductive inhibition during winter conserves energy at a time when the odds of producing viable young are low. In addition to the well-studied seasonal cycles of mating and birth, there are also significant seasonal cycles of illness and death among many populations of mammas and birds in the field. Challenging winter conditions, such as low ambient temperatures and decreased food availability, can directly induce death via hypothermia, starvation or shock. In some cases, survival in demanding winter conditions puts individuals under great physiological stress, defined here as an adaptive process that results in elevated blood levels of glucocorticoids. The stress of coping with energetically demanding conditions can also indirectly cause illness and death by compromising immune function. Presumably, the increased blood concentrations of adrenocortical steroids in response to winter stressors compromise immune function and accelerate catabolic mechanisms in the field, although the physiological effects of elevated glucocorticoids induced by artificial stressors have been investigated primarily in the laboratory. However, recurrent environmental stressors could reduce survival if they evoke persistent glucocorticoid secretion. The working hypothesis of this article is that mechanisms have evolved in some animals to combat season stress-induced immunocompromise as a temporal adaptation to promote survival. Furthermore, we hypothesise that mechanisms have evolved that allow individuals to anticipate periods of immunologically challenging conditions. A review of the effects of photoperiod on immune system function in laboratory studies reveals that exposure to short day lengths enhances immune function in every species examined. Short day exposure in small mammals cause reproductive inhibition and concomitant reduction in plasma levels of prolactin and steroid hormones as well as alterations in the temporal pattern of pineal melatonin secretion. Conclusion: day length appears to affect immune function in many species, including animals that typically do not exhibit reproductive responsiveness to day length.|
The RGCSA has an agreement with the AA, the publishers of the research Journal Correlation, to make articles contained in the journal available by request and on observation of copyright rules. If you wish to request full copies of any of the abstracted articles from Correlation contained on the RGCSA database you can do so by completing and returning, with payment, the articles request form. This form should be completed and downloaded so that you may sign the copyright declaration contained within it. When the AA has received this form, with your signature, together with payment, the article will then be despatched to you, normally within fourteen days of receiving your request. For copyright reasons you must sign the form and return it before a copy of the article can be released to you. UK copyright law currently insists on actual signatures so an electronically mailed signature is not acceptable. We look forward to receiving your requests and hope that you will enjoy this new service.
© 2009 Research Grants for the Critical Study of Astrology