What can microdialysis tell us about the temporal and spatial generation of cytokines in allergen-induced responses in human skin in vivo?

This study examined the suitability of microdialysis to assess the time course of cytokine generation from discrete sites within the skin following intradermal injection of allergen. Cytokines were recovered using two microdialysis probes, one close to the point of allergen injection and the other 1 cm away but within the area of the late-phase induration. Skin biopsies taken at both sites were stained immunocytochemically to investigate possible relationships between cytokine generation, expression of adhesion molecules, and recruitment of neutrophils and eosinophils during the late-phase allergic response. The cytokine response to probe insertion was assessed using a single probe in the opposite arm (control). At baseline, microdialysate contained low levels of IL-1alpha, IL-5, IL-8, IL-12, GM-CSF, and TNFalpha (n=27-33). At control sites, this was followed by increases in IL-6 and IL-8 at 3 and 6 hours. Allergen increased TNFalpha levels in 3/11 individuals within 30 minutes at the injection site. Levels of IL-6 and IL-8 rose rapidly and were significantly greater (P<0.05) than that of controls at 3 and 6 hours at both injection and distant sites. Adhesion molecule expression and leukocyte infiltration were elevated only at the allergen injection site, suggesting a complex relationship between cytokine generation and cellular events in allergic inflammation. In conclusion, microdialysis can be used to distinguish temporal and spatial changes in protein profiles in the skin. Furthermore, when used in conjunction with skin biopsies, it provides novel information about the mechanisms of dermal inflammation.