Technical prerequisites for in vivo microdialysis determination of interleukin-6 in human dermis

Background Cutaneous microdialysis in vivo in human skin is demonstrably of use in the study of skin metabolism, percutaneous absorption and skin inflammation. A promising area for cutaneous microdialysis is the measurement of cytokines. This requires catheters equipped with membranes permeable to molecules of high molecular weight. Objectives To address technical problems of poor sample volume retrieval and analysis sensitivity in the simplest model of provocation, namely the insertion of the catheter itself in vivo into human dermis. Methods Use of a polyethylenesulphone membrane, with a cut-off value of 100 000 Da, allowed measurement of target molecules of large molecular weight. Using an adaptation of a commercially available high sensitivity enzyme-linked immunosorbent assay, the ubiquitous proinflammatory cytokine interleukin (IL)-6 was measured in the normal skin of six healthy volunteers after insertion of the microdialysis catheter. Results Reliable sample volumes and high analyte recovery were achieved either by push-pull pumping or by standard pumping using a perfusate consisting of Ringers Dextran 60 Braun. No IL-6 was detected in 25 of 26 samples taken during the first 100 min after catheter insertion. The IL-6 concentration then increased and remained elevated for the duration of the experiments. Conclusions Technical and analytical modifications in the microdialysis technique have allowed the measurement of IL-6 in vivo in human dermis. It is suggested that the cytokine production is the result of the dermal trauma caused by catheter insertion, but the cellular source of the IL-6 is at present unknown.