Thermal cum lipopolysaccharide-induced stress challenge downregulates functional response of bovine monocyte-derived macrophages

Macrophages are considered to be key players in innate immunity and inflammatory responses. Domestic cattle with standard body size quickly reach their heat tolerance limit and are prone to heat stress. The combined effects of high temperature and endotoxemia on bovine monocyte-derived macrophages remain almost undisclosed. This study aims to unravel the molecular and functional responses of bovine monocyte-derived macrophages to thermal cum lipopolysaccharide induced stress challenge in vitro. The cells were incubated at 37 °C or 40 °C with lipopolysaccharide (1.0 μg/mL) for 24 h and 48 h. At the end of each treatment, cell viability, apoptotic rate, mitochondrial membrane potential, oxidative activity, phagocytosis, and autophagy functions were assessed and mRNA abundance of genes related to heat shock (HSP 70), inflammation (IL1β, IL6, IL 12, TNF, INF γ), cell signalling (TLR4), cell viability (Bax, Bcl2), nitric oxide synthesis (NOS2) and natural resistant associated macrophage protein were quantified by quantitative polymerase chain reaction (qPCR). The results revealed the increased apoptosis, reduced mitochondrial membrane potential, and cell viability, decreased oxidative and phagocytosis ability in cells co-stimulated with LPS and thermal stimuli. Upregulation of HSP 70 gene and downregulation of natural resistant associated macrophage protein, cell signalling, and inflammation related genes mRNA expressions were also identified due to these stressors. In conclusion, the observed thermal cum LPS stress induced dysregulation in macrophage functionality may be one facet of the increased disease susceptibility in dairy cattle during thermal stress.