Role of cytokines in mediating mechanical hypernociception in a model of delayed-type hypersensitivity in mice

In the present study, we used the electronic version of the von Frey test to investigate the role of cytokines (TNF-α and IL-1β) and chemokines (KC/CXCL-1) in the genesis of mechanical hypernociception during antigen-induced inflammation in mice. The nociceptive test consisted of evoking a hindpaw flexion reflex with a hand-held force transducer (electronic anesthesiometer) adapted with a 0.5mm2 polypropylene tip. The intraplantar administration of methylated bovine serum albumin (mBSA) in previously immunized (IM), but not in sham-immunized (SI) mice, induced mechanical hypernociception in a dose-dependent manner. Hypernociception induced by antigen was reduced in animals pretreated with IL-1ra and reparixin (a non-competitive allosteric inhibitor of CXCR2), and in TNF receptor type 1 deficient (TNFR1−/−) mice. Consistently, antigen challenge induced a time-dependent release of TNF-α, IL-1β and KC/CXCL-1 in IM, but not in SI, mice. The increase in TNF-α levels preceded the increase in IL-1β and KC/CXCL1. Antigen-induced release of IL-1β and KC/CXCL1 was reduced in TNFR1−/− mice, and TNF-α-induced hypernociception was inhibited by IL-1ra and reparixin. Hypernociception induced by IL-1β in immunized mice was inhibited by indomethacin, whereas KC/CXCL1-induced hypernociception was inhibited by indomethacin and guanethidine. Antigen-induced hypernociception was reduced by indomethacin and guanethidine and abolished by the two drugs combined. Together, these results suggest that inflammation associated with an adaptive immune response induces hypernociception that is mediated by an initial release of TNF-α, which triggers the subsequent release of IL-1β and KC/CXCL1. The latter cytokines in turn stimulate the release of the direct-acting final mediators, prostanoids and sympathetic amines.