Abstract
Cold stress syndrome (CSS) in Florida manatees represents on average 10% of the cause of mortality for stranded carcasses annually. That number can vary depending on the severity of the winter. For example, an early, cold winter in 2010 resulted in 36.8% of stranding mortality attributed to CSS, while over a mild winter (2013) only 5% mortality from CSS was observed. Upon necropsy, manatees with cold stress syndrome show physical symptoms associated with suppressed immunity, suggesting they are more susceptible to secondary opportunistic infections.1-3 Cytokines are innate and adaptive immune proteins known to have important roles in the mammalian response to viral and bacterial infections, trauma, and wound healing.4 Xenograft models have shown that relative to genes that do not change their expression in response to a stimulus, differentially expressed mRNA levels correlate more closely with protein levels.5 Therefore, by looking for differentially expressed cytokine mRNA in cold stressed manatees, we may more directly understand the specific cytokine pathways being affected.
We used species-specific quantitative, real-time PCR (qPCR) assays to measure mRNA expression of genes associated with immune function in Florida manatees.6 Blood samples were obtained from adult to subadult manatees during health assessments in Brevard County, FL during December of 2010 (n=10) and 2013 (n=10). Samples from 2010 were from manatees confirmed for CSS, and 2013 samples were from manatees with no signs of CSS (comparison group). Manatees from the CSS group displayed significant reductions in IL-2, IL-10, and TNF-α, while levels of IL-6 and the internal control gene β-actin remained unchanged. Reduced cytokine expression was hypothesized based on previous manatee immune studies, which have shown CSS to suppress lymphocyte proliferation.7 Such a reduction in these cytokines would likely inhibit a manatee’s response to infection and specifically may hinder the acute phase reaction, an important part of the early innate immune response to initial insults. This study begins to fill in a gap in our understanding of the immunosuppressive effect of cold stress in the Florida manatee. Further characterizing the direct or indirect nature of cold stress on immune function is important to inform and improve their treatment following future live strandings.
Acknowledgements
The authors wish to thank Emily Benzie, the Florida Fish and Wildlife Conservation Commission, the University of Florida College of Veterinary Medicine Aquatic Animal Health program, and the rest of the members of the USGS Sirenia project for their contributions to this study. Our study was carried out as part of the U.S. Geological Survey (USGS) Sirenia Project (USFWS Research permit: MA-791721, USGS IACUC permit: USGS-WARC-2016-03).
*Presenting author
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