Immunostaining of human tonsil and in disorders characterized by reactive pDCs. Top 2 rows: pDCs express the Toll-like receptors TLR7 and TLR9 (immunoperoxidase staining, hematoxylin counterstain). Vess indicates vessel. Double immunofluorescent labeling shows coexpression in pDCs of TLR7 and CD2AP. Third row, left: The interfollicular area contains cells stained for the pDCs marker CD2AP (brown) and also TdT-positive cells (red), but it is evident (see high magnification inset) that these 2 populations do not overlap (hematoxylin counterstain). Right: Double immunoenzymatic staining for CD123 (brown) and BCL11A (blue) shows coexpression in pDCs. The nuclei in the background with weak staining for BCL11A are B cells (no counterstain). Fourth row: The clusters of pDCs that accumulate in cutaneous lupus (revealed by immunostaining for CD2AP) are morphologically identical to those seen in tonsil and blood and show no evidence of dendritic processes (immunoperoxidase staining, hematoxylin counterstain). In Kikuchi disease, large clusters of pDCs are seen, some of which have increased cytoplasm, and they show the same pattern of marker expression as normal pDCs, for example, positive for the cytoplasmic marker CD2AP (brown or red) and for the transcription factors BCL11A (red) and ICSBP/IRF8 (brown; immunoperoxidase and double immunoenzymatic staining, hematoxylin counterstain). (Images were acquired on a Nikon Eclipse E800 microscope [Nikon, Tokyo, Japan] equipped with 20×/0.7, 40×/0.95, and 60×/1.4 Plan Fluor objective lenses [Zeiss], using a Zeiss Axiocam digital camera [Zeiss, Oberkochen, Germany], Axiovision 3 image acquisition software [Zeiss], and Adobe Photoshop 7 image processing and manipulation software [Adobe, San Jose, CA].)