Moderate temperature alterations affect Gram-negative immune signalling in ex vivo whole blood

Alterations in body temperature may influence immune system function and consequently affect the risk of infection and inflammatory diseases. Lipopolysaccharide (LPS) from gram-negative bacteria induces production of inflammatory cytokines after ligand binding to Toll-like receptor 4 (TLR4) on immune cells (especially monocytes/ macrophages). Our aim was to explore how clinically relevant hypo- and hyperthermia affect this signalling in an ex vivo whole blood model, and investigate if the cytokine response was correlated with monocyte TLR4 expression level.

Blood from 11 healthy volunteers was incubated with LPS 10 ng/ml for 6 h at 33, 37 or 40°C. The concentrations of selected pro-inflammatory (tumour necrosis factor-α (TNF-α) and interleukin (IL)-1β) and anti-inflammatory (IL-10) cytokines were measured in plasma, and the surface expression of TLR4 was quantified on CD14 + monocytes.

Monocyte TLR4 expression and plasma IL-1β were inversely related to temperature. The TNF-α production was unaffected by hypothermia but increased significantly during hyperthermia, whereas plasma IL-10 was significantly reduced during both hypo- and hyperthermic incubation. No correlation was found between TLR4 expression and cytokine concentrations. During hypothermia, the TNF-α/IL-10 and IL-1β/IL-10 ratios increased seven and nine times, respectively. Hyperthermia increased the TNF-α/IL-10 ratio, but to a lesser extent (doubling), whereas the IL-1β/IL-10 ratio remained unchanged.

Hypothermia significantly changed the cytokine ratios in the pro-inflammatory direction. In comparison, the effect of hyperthermia was sparse, with a modest increase in the TNF-α/IL-10 ratio only. No association was found between LPS-stimulated cytokine production and TLR4 expression on CD14 + monocytes.