[Significance of CD123 in histiocytic necrotizing lymphadenitis].

OBJECTIVE: To investigate the mode of presentation, cytologic features of the plasmacytoid dendritic cells (pDC), and the expression of CD123 and its significance in Kikuchi's disease. METHODS: CD123 expression was evaluated by EliVision immunohistochemical staining in formalin-fixed and paraffin-embedded tissues from 30 cases of Kikuchi's disease, 5 cases of T cell lymphoma, 10 cases of reactive lymphoid hyperplasia and 10 cases of chronic tonsillitis. RESULTS: Clusters of CD123 positive PDC were observed in Kikuchi's disease (28 of 30 cases, 93.3%) and the staining intensity was more prominent in the PDC at the periphery of the lesion and around the high endothelial venule-like vessels. CD123 showed three staining patterns: membranous (10 cases, 33.3%), cytoplasmic (10 cases, 33.3%), and membranous and cytoplasmic (8 cases, 26.7%). In the control group, CD123 showed cytoplasmic staining in reactive hyperplasia and chronic tonsillitis. Regarding the staining intensity, 12 of 28 cases (42.9%) were 3+ for CD123, 8 of 28 cases (28.6%) were 2+, and 8 of 28 cases (28.6%) were 1+. In contrast, PDC clusters with 1+ staining intensity were observed in 1 of 10 cases of reactive lymphoid hyperplasia; 2 of 10 chronic tonsillitis diseases; and much less in T cell lymphoma. CONCLUSIONS: Large cluster of PDC is detected in both proliferative and necrotizing types of Kikuchi's disease, making this a useful adjunctive diagnostic marker.