Oral Presentation International Veterinary Immunology Symposium 2016

Effect of season on lymphocyte-mediated inflamm-aging and immunosenescence in the horse (#70)

Melissa H. Siard 1 , Brooke M. Hadley 1 , Alejandra Betancourt 1 , John C. Stewart 1 , David W. Horohov 1 , Amanda A. Adams 1
  1. Gluck Equine Research Center, University of Kentucky, Lexington, KENTUCKY, United States

Many species including the horse exhibit various changes of the immune system associated with old age, which can prove detrimental to health. The two key categories of age-associated changes include: inflamm-aging (chronic, low-grade inflammation occurring systemically) and immunosenescence (decreased immune response). Season has influenced immunity in other species but has not yet been investigated in the horse. In order to better understand when senior horses may be prone to disease, a basic knowledge of seasonal changes in immune function is beneficial. Furthermore, knowing whether season affects immunity will aid in experimental design. Peripheral blood mononuclear cells (PBMC) were collected from n=8 senior horses (mean age = 23.38±1.66 yr) and n=8 adult horses (mean age = 10.75±0.83) each month for a year.  PBMC were then stimulated, intracellularly stained for interferon-gamma (IFNg) and tumor necrosis factor-alpha (TNFa), and analyzed via flow cytometry. PBMC were also stimulated, fluorescently tagged, and analyzed via flow cytometry to determine lymphocyte proliferation. Two-way ANOVAs with repeated measures were used to determine the differences in immune measures between senior and adult horses over time. As expected, senior horses exhibited significantly (p<0.05) more inflammation than adult horses for all inflammatory measures (including percent of lymphocytes producing IFNg and TNFa as well as mean fluorescence intensity for IFNg and TNFa). Senior horses and adult horses exhibited changes over time for all inflammatory measures and lymphocyte proliferation (p<0.05). Inflammation appears to be consistently elevated the most in the spring, while lymphocyte proliferation is highest in the fall. Season plays a role in multiple markers of immune function; therefore, having a control group is essential to research involving horses, even for short-term studies. Furthermore, senior horses display seasonal changes in their already elevated levels of inflammation as well as displaying seasonal changes in lymphocyte proliferation, which may have management implications.