IL-10 production is reduced by hypothermia but augmented by hyperthermia in rat microglia

Pro-inflammatory cytokines and nitric oxide (NO) are considered responsible for exacerbating brain injury. Activated microglia produce these potentially cytotoxic factors during neuron destruction. The beneficial effects of hypothermia on neuroprotection are considered to be due, in part, to suppression of post-injury inflammatory factors by microglia. However, the underlying mechanisms remain unclear. In particular, the hypothermia's role in modulating anti-inflammatory cytokines is unknown. We examined whether altering culture temperature modifies microglial production of cytokines and NO. Microglia isolated from neonatal rats were cultured with 1 microg/mL lipopolysaccharide (LPS) under hypothermic, normothermic, and hyperthermic conditions for 72 h. Interleukin (IL)-6 and IL-10 levels in supernatants were measured by enzyme-linked immunosorbent assay (ELISA). NO production was analyzed by colorimetric assay of nitrite accumulated in the medium. Compared to normothermia, hypothermia decreased LPS-induced IL-6 production at 6 h of culture. In contrast, hyperthermia reduced IL-6 production throughout culture. IL-10 production was reduced by hypothermia but augmented by hyperthermia at 24-72 h. NO production was reduced by hypothermia throughout culture, while no significant differences in NO production were observed between normothermia and hyperthermia. In this study, hypothermia reduced production of IL-6, IL-10, and NO by LPS-activated microglia, suggesting that the neuroprotective effects of hypothermia might involve not only the inhibition of inflammatory factors, but also anti-inflammatory factor(s). Hyperthermia specifically increased IL-10 production in these cells. These temperature-dependent changes in IL-10 production may imply an important clinical marker for this cytokine in hypothermia-related neuronal protection and in hyperthermia-related neuronal injury.