Cutaneous Reactive Histiocytosis in Golden Retrievers: An Immunohistochemical Approach

Canine cutaneous reactive histiocytosis (CRH) is a proliferative histiocytic disease characterised by the accumulation of dendritic cells (DCs). Differentiating CRH from other infectious or non-infectious granulomatous or histiocyte-rich diseases is challenging on histological evidence alone.

This study aims to characterise the predominant histiocytic population in 11 golden retrievers with histological features compatible with CRH, using ionised calcium-binding adapter molecule 1 (Iba1) and a validated macrophage antibodies cocktail for canine skin diseases.

Eleven golden retriever dogs were enrolled with a clinical and histological diagnosis of CRH.

Paraffin-embedded skin biopsy samples from cases with a confirmed diagnosis of CRH were evaluated to identify the histiocytic cell type. Two antibody reagents were used: (1) anti-Iba1 (goat polyclonal), a broad histiocytic marker and (2) a cocktail of rabbit recombinant monoclonal antibodies against CD11b, CD68, CD163, CD14 and CD16 to phenotype cutaneous macrophages.

All cases showed positive immunostaining with both antibodies. Although Iba1 immunostaining was diffuse in most of the histiocytoid cell population, only a few scattered histiocytoid cells stained with the anti-macrophage antibody cocktail.

Strong Iba1 positivity in the histiocytoid cells, together with their lack of staining for macrophage markers, supports a dendritic cell phenotype and is consistent with a diagnosis of CRH. In conclusion, using a macrophage marker in combination with a broad histiocytic marker may help to distinguish CRH from granulomatous, macrophage-rich diseases in paraffin-embedded skin tissue.