Histopathological analysis of CD163 and myeloperoxidase expression in neutrophil-rich dermatoses

Background Predominance of myeloperoxidase immunoreactive mononucleated cells in the dermal infiltrate defines histiocytoid Sweet’s syndrome. These cells are believed to represent immature myeloid cells of granulocytic lineage, and the authors suppose that they could be present in other neutrophil-rich inflammatory dermatoses. Aim This report aimed to investigate CD163 and/or MPO expression on mononuclear cells in dermatoses with tissue neutrophilia not previously considered. Methods A double immunostaining protocol with CD163 and MPO primary antibodies was applied to skin biopsies of 4 groups of neutrophil-rich dermatoses: Sweet’s syndrome, acute neutrophilic vasculitis, type 2 leprosy reaction, and sporotrichosis. Results CD163 + MPO− and CD163 + MPO+ macrophages were present in all groups, ranging from less than 10% to more than 50% and from less than 10% to 10%‒50% of positive cells, respectively. CD163 − MPO+ histiocytoid cells were detected in all groups, except in the acute neutrophilic vasculitis group. Study limitations The present study was unicentric with a small number of cases, and then loss of a more refined statistical analysis. Conclusions Besides the identification of MPO immunoreactive macrophages by a double immunostaining protocol, CD163 − MPO+ histiocytoid cells were found not to be restricted to classic neutrophilic dermatosis, and tissue neutrophilia does not imply the presence of immature myeloid cells.