mDC-neutrophil interaction in skin biopsies from patients with MPO-ANCA–associated microscopic poliangiitis. (A) Double immunostaining with anti–DC-SIGN (purple) and anti-MPO (brown) shows mDCs intermingling with PMNs and populating the inflammatory infiltrate (top panels, black arrows; scale bars represent 25 μm). Higher magnifications highlight mDCs loaded with MPO (bottom panels, black arrows; scale bars represent 10 μm). (B) Within the inflammatory infiltrate involving dermal vessels of ANCA-associated MPA patients or in the skin of SLE patients, extracellularly located MPO, suggestive of NETs (black arrows), can be detected in close proximity with DC-SIGN⁺ cells (left panel, scale bar represents 25 μm; right panel, scale bar represents 10 μm). SLE skin biopsies also showed mDCs loaded with PMN apoptotic bodies (green arrows). On the other hand, in skin biopsies from psoriasis, DC-SIGN⁺ cells are not in contact with the few MPO⁺ cells that are present. (C) In situ immunofluorescence microscopy on the same samples highlighted the presence of NET (white arrows) in damaged areas as detected by DAPI nuclear staining (blue) and MPO (red; top panels). One representative biopsy from 1 of the 6 MPA patients analyzed is shown (original magnification ×40).