Apoptosis in histiocytic necrotizing lymphadenitis.

Cell death can now be divided into necrosis and apoptosis, which are different in their morphology, biochemistry and biological significance. The present study was designed to investigate cell death in histiocytic necrotizing lymphadenitis (HNL). The features of cell death in 10 cases of HNL were analyzed using histiomorphology, ultrastructure and in situ apoptosis detection (ApopTag) methods. Two patterns of cell death were discerned. One was apoptosis of individual cells and the other was necrosis. The first pattern could be observed in all cases and the morphological features of the dead cells were consistent with those of apoptosis, which included distinctive cell volume shrinking and chromatin condensation. The apoptotic cells and bodies could frequently be found to be phagocytosed by the histiocytes. ApopTag was positively stained in most of the morphologically apoptotic cells. By double staining, most ApopTag positive cells were found to be T lymphocytes. A previous report showed that the majority of the proliferative cells were T lymphocytes. Based on those results, if was speculated that the main pathological characteristics of HNL therefore consisted of apoptosis and the proliferation of T lymphocytes.