Ovine lameness due to foot diseases has a major impact on animal welfare and economy, estimated to cost the UK sheep industry £24–80 million p.a. in treatment and lost production. The interdigital skin of the ovine foot is constantly exposed to a wide variety of microbes, most of them commensal. In addition, interdigital skin is frequently damaged, allowing opportunistic invasion of benign microbes as well as facilitating invasion of pathogens. In sheep, footrot is attributed to a mixed infection of Fusobacterium necrophorum and Dichelobacter nodosus and develops via an intermediate interdigital dermatitis (ID). The innate immune system is of crucial importance for the host response to pathogens and in the process of inflammation. Currently, there is only very limited knowledge on the innate immune response at the ovine skin hoof interface.
This study aimed to investigate the innate immune response to footrot by using quantitative PCR to determine the expression of Toll-like receptors (TLRs) and pro-inflammatory cytokines using two different approaches: (1) Post slaughter biopsy samples of the skin-hoof interface of sheep displaying signs of ID and footrot in comparison to healthy feet. Expression of TLR2, TLR4 and IL-1β was increased in biopsies from feet with ID and significantly increased in samples displaying footrot. (2) Stimulation of primary ovine dermal fibroblasts, the main cell type of the dermis that plays an important role in modulating leukocyte behaviour and function and shape the tissue microenvironment, with heat-killed F necrophorum and D nodosus or both, resulting in significant increases in TLR2 expression.
In summary, TLR and pro-inflammatory cytokine expression is modulated at the skin-hoof interface during the inflammatory stages of footrot and dermal fibroblasts respond to footrot bacteria and contribute to the pro-inflammatory host response, providing a first insight into the innate immune response to ovine footrot.