Th2 Cytokines Inhibit Toll-Like Receptor 2 Mediated Epidermal Barrier Repair

Atopic dermatitis (AD) is characterized by Th2 inflammation and defects in epidermal tight junctions (TJ). We have shown that activating Toll-like receptor 2 (TLR2) on human keratinocytes enhances TJ integrity and AD epidermis has reduced expression of TLR2. These observations have led us to hypothesize that Th2 cytokines inhibit TLR2-mediated barrier repair. We utilized the STAT6VT mouse, which expresses a constitutively active STAT6, resulting in enhanced expression of Th2 cytokines. TJ barrier recovery following tape-stripping was quantified using transepidermal water loss (TEWL) and epidermal expression of TLR2 and TJ protein measured. TJ barrier recovery of tape-stripped skin from STAT6VT and WT ± stimulation with Pam3C (TLR1/2 agonist; ex vivo) was measured by transepithelial electrical resistance (TEER) and paracellular permeability. Pam3C-dependent TJ barrier recovery was also examined in human skin explants post tape-stripping ± Th2 cytokines. Barrier recovery (e.g. TEWL) following tape-stripping was impaired in STAT6VT mice (P<0.001). Pam3C enhanced TJ barrier recovery as measured by TEER (P<0.01) and paracellular permeability (P<0.01) in skin from WT, but not STAT6VT mice. Immunofluorescence staining of the epidermis from STAT6VT mice revealed reduced expression TLR2 and CLDN1 while ZO-1 staining had an abnormal punctate pattern. Th2 cytokines inhibited Pam3C-dependent TJ barrier recovery of tape-stripped human skin measured by TEER (P<0.01) and paracellular permeability (P<0.01). Th2-skewed STAT6VT mice have reduced epidermal TLR2 expression and diminished TLR2-dependent epidermal barrier repair. Th2 cytokines also reduced TLR2-dependent epidermal barrier repair in human skin. Inhibiting Th2 cytokines may improve epidermal barrier function in response to tissue injury or microbes.