Impacts of heat stress on baseline immune measures and a subset of T cells in Bama miniature pigs

Understanding the stress-associated mechanisms of immune system function and the increased susceptibility of livestock to disease is now more important than ever because the majority of emerging animal diseases have proven to be zoonotic diseases and, therefore, threaten public health. The objective of the present study was to explore the effect of a 21-day heat stress on total white blood cell (WBC) counts, differential counts, a subset of T cells, NK cytotoxicity and neutrophil phagocytosis in Bama miniature pigs aged approximately 3 to 4 months. Pigs were assigned to one of two treatment groups: stress (heat, n = 10) or control (no stress treatment, n = 10). The results showed that the number of total WBCs was decreased in heat stressed pigs at day 7 (P ≤ 0.05). The percentages of eosinophils and monocytes were significantly higher in stressed pigs than in control pigs at day 1 (P ≤ 0.05). The number of CD8 T cells, unlike the CD3 and CD4 T cell, was significantly increased in heat stressed pigs compared to control pigs at day 1 and day 14 (P ≤ 0.05). Consequently, the ratio of CD4 and CD8 T cells was reduced in stressed pigs compared to control pigs at day 14 (P ≤ 0.05). Neither neutrophil phagocytosis nor natural killer cytotoxicity differed between the treated and control pigs at any time. The results indicate that heat stress influences CD8 T cells and the ratio of CD4 and CD8 cells. This change may play an important role in immune suppression induced by high air temperature.