Cytokine mRNA expression in skin in response to ectoparasite infection

Cellular infiltration and local cytokine mRNA levels were examined during the first 48 h of infection of skin by larvae of the sheep blowfly Lucilia cuprina. At the cellular level the response involved a dramatic influx of leucocytes (CD45+ cells). Among these infiltrating cells were large numbers of granulocytes, including neutrophils and eosinophils, as well as macrophage-like cells and lymphocytes. Many of the lymphocytes expressed cell surface markers characteristic of T cells including CD4, CD8 and the gamma delta TCR. The numbers of each of these cell types increased progressively as infection continued so that by 48 h the lesions were densely populated. Expression of mRNA for IL-6 could be detected by Northern blot analysis while mRNA for other inflammatory cytokines including IL-1 alpha, IL-1 beta, IL-8 and TNF alpha was detected using the polymerase chain reaction. Coincident with the influx of granulocytes and other cells there was an increase in the level of mRNA for the cytokines IL-1 alpha, IL-1 beta, IL-6 and IL-8. In the skin of the sheep there appeared to be constitutive expression of message for the cytokines IL-1 beta, IL-6 and TNF alpha, with the level of the latter not found to increase during the 48 h of infection examined. In situ hybridization was used to determine the location of IL-6 and TNF alpha mRNA within resting and infected skin. During infection, fibroblasts, macrophage-like cells and endothelium appeared to produce high levels of IL-6 mRNA. Expression of the T cell dependent cytokines IL-2 and IFN-gamma but not IL-4, increased in expression as time progressed and the population of infiltrating cells, including T cells, expanded.