Inflammasome activation in delayed-type hypersensitivity reactions.

The inflammasome is a protein complex cleaving the pro-inflammatory cytokines IL-1beta and IL-18 into their active forms by caspase-1 activation. The cytosolic protein complex can be activated by danger signals, such as bacterial and viral components, ATP, or uric acid crystals, and reacts as a sensor of innate immunity. In the skin, sensitizing agents promote induction of specific T-cell-mediated contact hypersensitivity. They induce dendritic cell migration, a precondition for the priming of specific T cells. They are a prerequisite for the recruitment of cells into the skin that demand pro-inflammatory stimuli, such as IL-1beta and IL-18. Watanabe et al. (2007, this issue) demonstrate the presence of the inflammasome complex in keratinocytes and report that this complex can be activated by contact sensitizers, such as trinitrocholorobenzene (TNCB), both in vitro and in vivo. The study documents a regulatory effect of innate immunity in a T-cell-mediated delayed-type hypersensitivity reaction.