Alterations with age in peripheral blood lymphocyte subpopulations and cytokine synthesis in beagles

Megumi Fujiwara,^1,2 Tomohiro Yonezawa,³ Toshiro Arai,¹ Ichiro Yamamoto,¹ Hiromichi Ohtsuka<sup>2

1</sup>Laboratory of Veterinary Biochemistry, Nippon Veterinary and Life Science University, Tokyo, Japan; ²Laboratory of Large Animal Internal Medicine, ³Laboratory of Veterinary Physiology, Kitasato University, Towada, Japan

Purpose: The immune system is considered to be affected by aging, which is linked to various immune pathogeneses. The purpose of this study was to determine age-associated changes in immune function of healthy dogs (beagles), specifically those of naive and memory T lymphocytes, based on cytokine synthesis.
Patients and methods: Blood samples were obtained from 44 healthy beagles that were divided into three age-groups: young (<4 years), middle-aged (4–8 years), and older dogs (>8 years). Subpopulations of T lymphocytes were determined by flow cytometry. Transcriptional (mRNA) levels of cytokines were determined for primary-cultured leukocytes using quantitative real-time polymerase chain reaction.
Results: There were negative correlations between dogs’ages and the number of peripheral blood mononuclear cells, T cells, and B cells. In particular, the number of naive CD4⁺ CD45RA⁺ T cells and CD8⁺ CD45RA⁺ T cells significantly decreased with age. The mRNA levels for interleukin (IL)-2, IL-2Rα, and interferon-gamma were significantly higher in young or middle-aged dogs (P < 0.05), whereas IL-4 mRNA expression was not significantly different over the different age-groups. IL-2Rγ mRNA expression tended to decrease with age.
Conclusion: Decreases of naive CD4⁺ and naive CD8⁺ T cells may be related to age-related immunosenescence in dogs. With regard to cytokine production, leukocyte IL-4 and IL-10 mRNA levels did not change with age, whereas IL-2, IL-2Rα, and IL-2Rγ mRNA levels decreased with age. These altered cytokine mRNA expression patterns may contribute to decreased naive T-cell function(s) with aging.

Keywords: aging, leukocyte subpopulation, cytokine, dog, naive T cell, IL-2R