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Heat stress and endotoxin exposure alter expression of pro‐inflammatory and anti‐inflammatory cytokines in RAW 264.7 macrophages (815.3)

Heat stress results in significant homeorhetic changes in the body to enhance survival during this condition. Although the immune system plays a critical role in defense against pathogens, the impact of heat stress on this system is poorly understood. Therefore, this study was conducted with the objective of determining the impact of ambient temperature on cytokine expression in the RAW 264.7 macrophage model. Cells at confluence were exposed to either control (37 oC) or heat stress (41.5 oC) conditions for 24 hours before being challenged with LPS (10 ng/ml) for an additional 3 hours. Thereafter, RNA was extracted and reverse transcribed for RT‐PCR analysis. Expression of pro‐inflammatory M1 macrophage markers (TNFα, INOS, IL‐6, and IL‐1β) and anti‐inflammatory M2 markers (IL‐10 and Arginase 1) were determined. Heat stress resulted in significant upregulation of INOS, IL‐1β, and IL‐6. On the contrary, heat stress led to downregulation (P < 0.05) of expression of TNFα and tended (P < 0.1) to downregulate IL‐10. Treatment with LPS resulted in significant upregulation (P < 0.05) of all genes. There was significant interaction between ambient temperature and endotoxin exposure on the expression of a few genes. An additive effect of heat stress and endotoxin in stimulating the expression of INOS, IL‐1β, IL‐6 was obtained, whereas induction of TNFα by LPS was significantly lower in heat stress than in control temperature. These results suggest that heat stress results in significant modification of macrophage response to immune challenge in a way that could have significant implication for the regulation of immune response in animals during heat stress.