Toll-like receptors 2 and 4, and acute phase cytokine gene expression in dexamethasone and growth hormone treated dairy calves.

Cattle are exposed to growth hormone stimulants and to stressors that cause cortisol release. Both of these hormones affect immune responses which may reduce disease resistance. Toll-like receptors are the pattern recognition molecules of pathogens that are on immune cells. They then orchestrate the induction of the appropriate acute phase cytokines of the early innate response. The objective of this study was to determine changes in toll-like receptors and acute phase cytokines following treatment with a synthetic glucocorticoid (dexamethasone) and growth hormone (GH). Twenty-eight calves were given the control (Cnt), dexamethasone (DEX), GH, or dexamethasone and GH (Both) treatments from 3 until 56 days of age. Blood was collected by jugular venipuncture on days 14, 28, 42, and 56. On day 56, a lung lavage was performed and spleen and thymus tissues collected. Total RNA was extracted from blood leukocytes, lung lavage cells, spleen and thymus cells. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was used to quantify interleukin-1 (IL-1), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor (TNF)-alpha, toll-like receptor 2 (TLR2), and toll-like receptor 4 (TLR4). Blood leukocytes had a time effect for IL-1Ra (P < 0.01), with a trend for a treatment effect (P = 0.07) and had a treatment by time interaction (P < 0.05). IL-1, TNF, and TLR2 and TLR4 were greatest (P < 0.05) for Cnt only at day 14. IL-1 expression of lung lavage cells was greatest (P < 0.05) for calves on the Both treatment compared to the other three treatments. However, IL-1Ra was not different among the treatments. Toll-like receptor 2 expression was enhanced with Both compared to either DEX (P < 0.05) or GH (P < 0.05) and tended to be greater than Cnt expression (P = 0.07). Expression of TLR4 tended to be reduced by Both compared to Cnt (P = 0.06). Tumor necrosis factor-alpha was greatly enhanced by Both compared to the other three treatments (P < 0.05). Spleen cell tended to have different IL-1 expression between GH and Both (P < 0.10). Interleukin-1 receptor antagonist and TLR2 and TLR4 were not different among treatments. However, TNF-alpha expression was enhanced by the DEX treatment alone compared to the GH treatment (P < 0.05), and tended (P < 0.10) to be greater than Cnt expression. None of the gene expressions were different among treatments for thymus cells. Lung lavage cell expression appears to be most susceptible to these hormones while blood leukocyte expression was only slightly affected, and thymus cells were not affected at all. These data demonstrate that TLR2 and TLR4 and acute phase cytokine expression can be altered by stress and growth hormones, which may decrease resistance of those animals to disease.