Myeloperoxidase positive histiocytes in subacute necrotizing lymphadenitis express both CD11c and CD163

Background and aim: Immunophenotype analysis of lesional histiocytes in subacute necrotizing lymphadenitis (SNL) has revealed several unexpected findings. Histiocytes express myeloperoxidase (MPO), and immature dendritic cells occupy a significant proportion of the lesional cells in SNL. However, whether MPO-expressing lesional histiocytes of SNL also express immunophenotypic markers of immature dendritic cells has not been determined. Methods: The immunophenotypes of lesional histiocytes in paraffin-embedded tissue sections from 26 patients with SNL were analyzed using a panel of dendritic cell and macrophage markers. Double immunohistochemical staining was also performed to confirm coexpression of several markers. Results: CD11c-expressing histiocytes represented a major component of lesional cells (averaging 50.1% of the lesional area), surpassing CD163-positive histiocytes (averaging 32.0% of the lesional area). Double immunohistochemical staining confirmed that a significant proportion of CD11c-expressing histiocytes also coexpressed MPO as well as CD163. CD123-positive plasmacytoid dendritic cells (averaging 3.2% of the lesional area) were minor lesional cells, and fascin-positive mature dendritic cells were not present in the lesions. Conclusions: Our results demonstrate that the main lesional cells in SNL are histiocytes expressing myeloid dendritic cell and macrophage markers as well as MPO, indicating phenotypic plasticity and functional versatility of histiocyte lineage cells.