Enhanced dendritic cells and regulatory T cells in the dermis of porokeratosis

Porokeratosis is characterized clinically by annular lesions and histologically by the presence of a cornoid lamella (CL) in the epidermis. The underlying mechanism of porokeratosis development remains unclear. We performed immunohistochemical staining of CD1a, langerin, Ki67, CD3, CD4, CD8, FOXP3, and RANKL (receptor activator of nuclear factor κB ligand) in samples from 17 porokeratosis lesions and analyzed the differences in staining patterns among the CL, the inner part of the annular ridge (IC), and the adjacent normal skin (ANS). Numbers of CD1a⁺ Langerhans cells in the epidermis were reduced and numbers of CD1a⁺ dermal dendritic cells were significantly increased in the CL and IC compared to those in the ANS. In addition, there was also an increase in FOXP3⁺ cells in the dermis below the CL and IC. Our findings suggest that Langerhans cells are downregulated in the epidermis in CL and that regulatory T cells and dendritic cells are upregulated in the dermis below the CL. This alteration in the distribution of immune cells, such as various lymphocyte subsets, Langerhans cells, and dermal dendritic cells, may play a key role in the pathomechanisms of porokeratosis.