The role of interleukin-17 (IL-17) in the pathogenesis of discoid lupus erythematosus and lichen planopilaris: is immunohistochemistry for IL-17 a promising way to differentiate these entities?

BACKGROUND: Interleukin-17 (IL-17) is a pro-inflammatory mediator which its excess secretion by immune cells is found in many chronic autoimmune diseases. This survey is aimed to compare the amount and pattern of distribution of IL-17 positive cells in lichen planopilaris (LPP) and discoid lupus erythematosus (DLE) which are of the most frequent causes of primary cicatricial alopecia (CA).

METHODS: Biopsies of lesional scalp skin from adult LPP (n = 30), DLE patients (n = 19), and control scalp skin (n = 18) were analyzed by immunohistochemistry (IHC) method using rabbit polyclonal antibody against IL-17. Cells stained positive for IL-17 and their pattern of distribution were assessed and compared between these groups.

RESULTS: The mean of IL-17 positive cell counts per high power field (HPF) in both LPP and DLE groups was significantly higher in comparison with the control group (both p < .0001). The LPP group had higher values of IL-17 positive cell counts per HPF (47.56 ± 13.37) compared to the DLE group (22.21 ± 11.06) (p < .0001). More than 30 IL-17 positive cell counts in IHC have a sensitivity of 90% and a specificity of 78% for differentiating LPP from DLE.

CONCLUSIONS: Our findings suggest that IL-17 is effective in the pathogenesis of DLE and LPP and its role is more prominent in LPP. IL-17 positive cells in IHC can distinguish DLE from LPP with satisfactory sensitivity and specificity.