Pathogenic roles of eosinophils in guinea-pig contact sensitivity: regulation of dermal eosinophilia with remotely administered IL-5.

Eosinophils have a variety of functions. Although increasing evidence links the presence of eosinophils to airway damage, studies have not examined in detail if, and how, eosinophils affect skin inflammation. The purpose of this study was to determine whether eosinophil infiltration augments the contact sensitivity reaction in vivo. Guinea-pigs were sensitized with 2, 4-dinitrochlorobenzene and challenged on the dorsal skin or on the right ear lobe. The number of eosinophils and macroscopic changes of the skin lesion in the presence or absence of human recombinant IL-5 (rIL-5) administered at the remote site was assessed. The reaction on the dorsal skin was acutely eczematous with considerable basophil infiltration. In contrast, eosinophils had extensively infiltrated the right ear lobe and major basic protein was deposited in the dermis. A subcutaneous injection of rIL-5 (10 pmol/kg) at the remote site (left ear lobe) 12 h after challenge induced transient blood eosinophilia and enhanced eosinophil accumulation in the challenged ear lobe. These changes were accompanied by increased ear swelling and severe erythema. In contrast, eosinophil infiltration was significantly inhibited by rIL-5 administered at the time of challenge. Ear thickness, as well as the erythema and oedema, were also reduced. These data suggest that marked eosinophil infiltration enhances skin inflammation in allergic contact dermatitis. Moreover, locally administered IL-5 functions remotely by controlling eosinophil recruitment into the skin. The guinea-pig model of contact sensitivity may be useful for evaluating therapies and pharmaceuticals targeted at eosinophil infiltration.