Toll-Like Receptors: Role in Dermatological Disease

Figure 1

(a) Cross-section of epidermis. Keratinocytes are present throughout the skin; other epidermal cell types include Langerhans cells, melanocytes, and merkel cells. (b) Keratinocytes express TLRs 1, 2, 3, 4, 5, 9, and 10. MD2: TLR4-associated molecule; MyD88: myeloid differentiation factor 88; $\text{NF-}\kappa \text{B}$: nuclear factor-$\kappa \text{B}$; TRAF-6: TNF receptor-associated factor-6; TRIF: TIR domain-containing adapter protein that induces IFN-$\beta$. (c) Langerhans cells express high levels of TLRs 2, 3, 4, 8, and 10. but express low levels of TLRs 1, 5, 6, 7, and 9. (d) Upon activation, myeloid-derived dendritic cells and to a lesser extent keratinocytes release IFNα and IL-18 which stimulate Langerhans cell maturation. With antigen stimulation the Langerhans cell induces a Th1 response. (e) In response to TLRs 2, 3, 4, 7, and 9 melanocytes initiate proinflammatory events via the illustrated pathways.

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