Immune response in the skin

Keratinocytes are the first defensive cells, expressing a wide range of PRRs (Pathogen Recognition Receptors) like TLR (TLR-1, TLR-2, TLR-4, TLR-5 and TLR-6) and c-type lectins; they also secrete a wide range of pro-inflammatory cytokines and antimicrobial peptides (AMPs). Indeed, keratinocytes can recognize PAMPs (Pathogen Molecular Pattern) by PPRs and trigger inflammation secreting interleukins (IL-1), IFNs, cytokines, growth factors , chemokines, defensins. They can also express MHCII and present antigen. The antigen trapped on the surface is captured and internalized by Langerhans cells (LC), a special subset of epidermal dendritic cells located between keratinocytes of the basal layer and the stratum spinosum. LCs process antigen and present it to the nearby helper T cells. In porcine epidermis, LCs have a typical dendritic cell (DC) morphology and express MHCII molecules and surface molecules such as CD1, CD172 and CD207. Epidermal LC are also necessary to sustain an effective cytotoxic response and