PSIX-7 Changes in circulating immune markers in aging canines indicate a modest Th1 bias.

Abstract Immunosenescence, characterized by a gradual decline in immune function, is one of the hallmarks of aging. T helper cells (Th cells), a subset of T-lymphocytes, that express CD4, a glycoproten, are a major source of cytokines. Based on the immune response and cytokines they produce, Th cells may be classified into Th1 cell-mediated immunity (IFNy, TNF-a) or Th2 humoral immunity (IgE, IL4, IL5, IL13). In human aging there is a general shift in the balance from Th1 to Th2 immunity. In canines, the shift towards a dominance of Th2 responses in aging is less clear, although both functions are likely reduced when compared to young. We, therefore, assessed circulating levels of cytokines and chemokines from whole blood collected in RNA PAXgene tubes from healthy dogs assigned to young (n=17, 2-4yr) and old (n=15, 10-13yr). Following RNA isolation, gene expression was measured using the NanoString’s nCounter® Canine immuno-oncology panel and analysis performed using the nSolver software. When assessing the top 60 genes that were significantly overexpressed there was a modest bias towards increase in markers of a Th1 response in older dogs when compared to young. However, the potential Th1 bias was not uniform as several, but fewer, Th2-associated markers were also upregulated in older dogs. There was a significant increase in the levels of Th1 associated cytokines IFNy and TNFa in older dogs (both p<0.05) but their expression levels were low. There was a significant increase in CCL5 (3.13 fold), CD160 (2.28), granzyme K (2.13), TBX21 (2.09), NKG7 (2.0), CD94 (1.98), Fas ligand (1.7), BST2 (tetherin, 1.68), CXCR6 (1.79), CXCR3 (1.65), CD70 (1.6), Lipocalin-2 (1.6), Perforin 1 (1.51), and PYCARD (1.5), markers generally associated with Th1 cells, in older dogs when compared to young (all p<0.05). In addition, there was also an increase in aconitate decarboxylase 1 (ACOD1, 1.65 fold; p<0.05) in older dogs, and an increase in ACOD1 may suppress Th2-mediated response. In contrast, fewer markers associated with Th2 cells were upregulated in older dogs including CCL4 (1.81), IL31RA (1.65), EpCAM (1.65), and IL1R1 (1.53) when compared to young (all p<0.05). Other cytokines generally associated with Th2 including IL4, IL5 and IL13 were barely detectable in either young or old dogs. Markers that did not strictly adhere to the Th1/Th2 classification but are components of T-cell or involved in T-cell functioning were increased in older dogs including TRGC2 (2.41), TGF☐2 (2.34), CD96 (2.03), ABCB1(1.68), and CD8A (1.67; all p<0.05 vs young). Whether the T-cells would show a similar bias upon activation in adverse health conditions is not clear and needs to be investigated. Our results indicate a more skewed Th1 profile which could serve as important nutritional targets to functionally activate cell-mediated immunity to fight infections in aging canines. Funding Sources: This study was funded by Hill’s Pet Nutrition, Inc.