Cutaneous cytokine gene expression and cellular responses in lambs infested with the louse, Bovicola ovis, and following intradermal injection of crude louse antigen

Abstract

The present study was undertaken to investigate further the immunological responses in the skin of lambs to natural louse infestation and following intradermal allergen challenge. Bovicola ovis-infested ( n = 7) and naïve ( n = 7) Romney lambs received four intradermal injections each of crude louse Ag and diluent control solutions on the dorso-lateral chest. From each lamb, skin samples were obtained from untreated skin and, at 4, 24, 48 and 72 h following injection, from one each of the Ag- and diluent-injected skin sites. Levels of acetylcholinesterase-positive Langerhans and MHC II + cells in the epidermis as well as MHC II +, CD1b +, T19 + and IgE + cells, eosinophils, and diffuse IgE staining in the dermis were significantly elevated in infested compared to naïve lambs (all p ≤ 0.01). Additionally, gene expression of interleukin-4 (IL-4), IL-5, IL-13 (all p ≤ 0.001) and IL-10 ( p ≤ 0.05) was significantly higher in the skin of infested compared to naïve lambs while TNF-α and IFN-γ gene expression were not significantly different between the two groups. Intradermal injection of louse Ag led to immediate and late phase responses in the infested lambs while the naïve lambs showed only minimal responses. Levels of dermal MHC II +, CD1b +, T19 +and IgE + cells, eosinophils and diffuse IgE staining in infested lambs following injection of louse Ag were similar to or exceeded those in untreated skin and, with few exceptions, were higher than in naïve lambs. Additionally, cytokine gene expression of IL-4, IL-5, IL-13 and IL-10 increased to peak levels 4 h following Ag injection in the infested lambs ( p ≤ 0.001, ≤ 0.05, ≤ 0.05 and ≤ 0.001 respectively compared to untreated controls) and remained significantly elevated compared to that observed in the naïve controls for the duration of the experiment. Significant elevations of MHC II + cells and IL-4, IL-5, IL-13 and IL-10 gene expression were observed in the louse-naïve lambs following injection of louse Ag but were much less pronounced than in the infested lambs. These results indicated that louse infestation in lambs elicited a highly skewed Th2 immuno-inflammatory response with many characteristics similar to those seen with other parasitic infections and also in atopic dermatitis.