IL-31 is a pruritogenic cytokine that is elevated in certain dermatoses such as bullous pemphigoid (BP), and atopic dermatitis (AD). In BP, eosinophils are the major reservoir of IL-31. The lesional IL-31 and eosinophil levels however, have not been investigated. We sought to evaluate whether IL-31 levels exhibited a correlation with lesional eosinophil levels in several eosinophil rich dermatoses.
A retrospective immunohistochemical analysis of IL-31 expression was performed on samples consistent with BP, AD, drug rash, arthropod assault, and non-BP eosinophilic spongiosis. Skin from lipoma excisions served as a negative control, and lichen planus (LP) samples were used as controls for
lymphocytic inflammation. Subsequently, for each sample, 4-micron sections were isolated, processed and stained. Basal and spinous keratinocytes were graded separately on a scale of 0 to 3, and a gradient was calculated by subtracting the spinous from the basal score. A Kruskal-Wallis test was used to
compare mean basal, spinous, or gradient scores between each disease. And a Spearman-Rank correlation was used to correlate mean basal, spinous, or gradient scores with eosinophil counts with significance defined as P<0.05.
Basal keratinocyte IL-31 scores correlated with local eosinophil counts in BP (R=0.706, P=0.003), though spinous levels did not (R=0.266, P=0.336). Amongst the diseases investigated, basal and spinous keratinocyte levels, as well as, the IL-31 gradient did not show any correlation with lesional eosinophils. Although, the epidermal IL-31 gradient showed a moderate correlation with lesional
eosinophil counts (R=0.408, P = 0.003), with removal of the BP cases this finding was shown to be no longer significant (R=0.246, P=0.188).
Herein, we demonstrated that epidermal levels of IL-31 correlate with lesional eosinophilia in BP, but not in other eosinophilic dermatoses. The disease specific microenvironment, with anti-basement membrane zone antibodies, and the cytokine milieu that follows may be the driving force behind eosinophil chemoattraction and local release of IL-31.

Lesional IL-31 correlates with local eosinophil counts in bullous pemphigoid but not other eosinophil rich dermatoses