Contribution of dermal macrophage trafficking in the sensitization phase of contact hypersensitivity

We investigated cellular trafficking of dermal macrophages that express a macrophage calcium-type lectin (MMGL) during the sensitization of delayed-type hypersensitivity. In skin, dermal macrophages, but not epidermal Langerhans cells, have been shown to express MMGL. Epicutaneous sensitization by FITC produced a transient increase in MMGL-positive cells in regional lymph nodes. To directly investigate whether the increase was due to cell migration from dermis, MMGL-positive cells purified from skin were intradermally injected into syngeneic mice after labeling with a fluorescent cell tracer, followed by epicutaneous sensitization over the site of injection. MMGL-positive cells containing the tracer were found in the regional lymph nodes after sensitization. The majority of the MMGL-positive cell migrants were negative for FITC fluorescence despite the presence of FITC-labeled cells that included Langerhans cell migrants. Because the extent of MMGL-positive cell migration was greatly influenced by the selection of vehicles to dissolve FITC, the efficiency of sensitization was compared using the ear swelling test. Migration of both Langerhans cells (FITC-labeled cells) and MMGL-positive cells contributed positively to the efficiency of sensitization. Interestingly, MMGL-positive cell migration was induced by vehicle alone, even in the absence of FITC. These results suggest that migration of dermal MMGL-positive cells accounts for the adjuvant effects of vehicles at least in part.