A case report of angioimmunoblastic T cell lymphoma (AITL) with localization of neoplastic clear cells in the outer zone of germinal centers

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Angioimmunoblastic T cell lymphoma (AITL) is characterized by the presence of atypical lymphocytes with clear cytoplasm and follicular dendritic cells, arborization of high endothelial blood vessels, and infiltration by inflammatory cells, such as epithelioid histiocytes, eosinophils, immunoblasts, and plasma cells. The neoplastic clear cells are localized around the high endothelial blood vessels or interfollicular areas. Recent reports have suggested that these neoplastic clear cells originate from helper T cells in germinal centers, based on their expression of CD10, PD-1, and CXCL13. We experienced a case of AITL which is histologically unique. A 61-year-old male presented to our hospital (Ogaki Municipal Hospital) with edema of his lower legs. Inguinal lymph node biopsy revealed that neoplastic clear T cells were mainly localized in the outer zone of germinal centers, specifically within the follicular dendritic cell (FDC) meshwork. Moreover, these cells were positive for CD3, CD4, CD10, CD43, CD45RO, PD-1, and weakly positive for CXCL-13. This is the first report showing that the neoplastic clear T cells were localized in the outer zone of germinal centers morphologically as well as immunohistochemically. In conclusion, this case report further supports the notion of germinal center helper T cell origin of neoplastic clear cells in AITL.

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