Major stress hormones suppress the response of macrophages through down-regulation of TLR2 and TLR4

Abstract

Background: Severe trauma often leads to diminished cytokines especially from macrophages to Toll-like receptor (TLR) agonists. However, the molecular mechanisms remain to be elucidated. As surgical trauma could also induce neuroendocrine hormones to modulate the immune system, we investigated the effects of major hormones, including endogenous glucocorticoid (corticosterone (CORT)), epinephrine (E), and norepinephrine (NE) on the expression and response of TLR2 and TLR4 in macrophages.

Materials and methods: Rat macrophages were pretreated by each hormone (1000 ng/mL of CORT, E, and NE) for 24 h, then restimulated with Pam3CSK4 or lipopolysaccharide (LPS) for further 24 h, and supernatant tumor necrosis factor-alpha (TNF-α) was measured. Additionally, macrophages were incubated with different concentrations of hormones (0-10,000 ng/mL) for 48 h or with 1000 ng/mL of hormones for 0-48 h, the expressions of TLR2 and TLR4 and intracellular molecules (MyD88, IRAK1, and TRAF6) in macrophages were analyzed by real-time quantitative polymerase chain reaction (PCR) and RT-PCR, respectively.

Results: Pam3CSK4-stimulated TNF-α production was significantly reduced from macrophages pretreated with CORT, and both Pam3CSK4- and LPS-stimulated TNF-α were suppressed with E. Moreover, CORT down-regulated only TLR2 expression in both time- and dose-dependent manner, but both TLR2 and TLR4 mRNA expressions were down-regulated in time- and dose-dependent manner after exposure to E. However, the transcript expression of MyD88, IRAK1, and TRAF6 remained unchanged after exposure to each hormone.

Conclusions: These results suggested that the down-regulation of TLR2 and TLR4 expressions by CORT and E is involved in the hyporesponsiveness of macrophages.