Assessment of heat stress response of peripheral blood mononuclear cells from dairy cows stress-phenotyped using bacterial lipopolysaccharide endotoxin

Heat stress (HS) can affect gut barrier integrity, leading to a leaky gut and elevated enteric bacterial LPS endotoxin levels in the circulation. This LPS can induce systemic inflammation manifesting as the acute-phase response, which includes a febrile response that may compromise heat dissipation from the body during HS. To assess the effects of HS, peripheral blood mononuclear cells (PBMC) were isolated from dairy cows that were previously stress phenotyped based on their 4-h serum cortisol response to Escherichia coli LPS (200 ng/kg administered i.m.). After stress phenotyping, a population of dairy calves (n = 260), 8 high stress responder (HSR; +1 SD from the mean, >956.0 pg/mL), 11 middle stress responder (MSR; ± SD around the mean of 573.4 pg/mL), and 11 low stress responder (LSR; -1 SD from the mean, <190.8 pg/mL) stress-responding animals were selected for the study. The PBMC were later isolated and subjected to a heat shock challenge (HSC) in vitro at 42°C for 4 h then returned to 37°C where the control plates remained. Cell viability and proliferation were assessed, culture supernatants were collected to assess cytokine and chemokine secretion, and total RNA was extracted to assess candidate gene expression. There was a significant increase in the apoptosis of PBMC from the HSR and MSR, as compared with the LSR group post-HSC. However, there was a significant increase in necrosis in the LSR PBMC as compared with other groups following HSC. Proinflammatory and anti-inflammatory cytokine and chemokine production, specifically IFN-γ, IL-8, and MCP-1, was influenced by HSC and different across treatment groups. Finally, there was a significant increase in the expression of HSP90 and HSP70 genes in HSC MSR PBMC compared with the CNT MSR PBMC. Collectively, these results demonstrate that PBMC from variable stress-responding cows respond differently to the HSC. Future research is warranted to investigate if this phenotype can be used to improve the HS resilience of dairy cattle through selective breeding.