Neutrophil recruitment in response to intradermal endotoxin challenge in man

Abstract Background Neutrophil recruitment is a key component of the innate immune response, but it is difficult to study in vivo in man, where multi-time-point samples from disease or challenge models are hard to obtain. In-vitro data from our group suggest that neutrophilic inflammation in response to endotoxin will be initiated by a cytokine cascade in which interleukin (IL) 1 has an early and important role. To study this in human beings, we have established a model of intradermal challenge. Methods Endotoxin and control solution (0·9% NaCl) were injected intradermally in the volar surface of the forearm of healthy volunteers. Serum was taken for blood count and C-reactive protein (CRP) measurements at 0, 1, 6, and 24 h. Temperature, blood pressure, and pulse were monitored. Sites were sampled by 4 mm punch biopsies at varying time points and after varying doses. Biopsy samples were analysed by immunohistochemistry and qPCR. Findings Intradermal erythema and mild oedema were seen over a current dose range of 0·01–15 ng endotoxin per site. Total dose per individual was 1 to 45 ng. No volunteer had significant systemic reactions. After 5 h, a peripheral blood neutrophilia was seen in some individuals. Erythema area increased up to 6 h, and there was a trend to larger area with larger dose. Above 1 ng endotoxin per site, neutrophilic infiltration of the skin was visible microscopically, but this was much greater at doses of 5 ng or greater. A significant difference was seen between neutrophil elastase stained biopsy area at 2 h and 6 h post administration of endotoxin for the higher doses. There were no changes in serum cytokine levels post injection. By contrast, qPCR revealed a rapid local generation of IL-8 mRNA, and more sustained expression of IL1α/β. Interpretation Intradermal administration of endotoxin within the limits described seems to be safe. It is an effective method of inducing significant local neutrophilic inflammation at an accessible site. Neutrophil infiltration of tissues starts before 2 h and continues beyond 6 h in response to a single dose of endotoxin. Neutrophilia (without CRP rise or symptoms), appears to be associated with a higher total endotoxin dose. IL-8 production at the inflamed site peaks early, whereas IL1α/β mRNA levels remain high at 6 h. Funding National Institute for Health Research.