Apoptosis- and cell cycle-associated gene expression profiling of histiocytic necrotising lymphadenitis

Cell death is of two types; necrosis and apoptosis. In histiocytic necrotising lymphadenitis (HNL), apoptosis is the main form of cell death. Apoptosis results in the formation of nuclear debris, which is one of the characteristic features of HNL. We previously reported that in HNL it is predominantly CD8-positive cytotoxic T cells that undergo apoptosis; however, the majority of proliferating cells are also CD8-positive T cells. Recent advances in technical and analytical methods have facilitated the parallel quantitation of expression of numerous genes using DNA microarrays. The technology is particularly well suited to compare differences in gene expression between normal tissues and inflammatory disease. To investigate the apoptosis- and cell cycle-associated gene expression in HNL, we analysed five cases each of HNL and non-specific lymphadenitis (NSL), using ready-made microarrays, including cyclins and caspases, and immunohistochemical staining of caspase-3, ssDNA, bcl-2 and NF-kappaB. Caspase-3- and ssDNA-positive apoptotic cells were frequently detected in HNL, but were rare in NSL. However, bcl-2- and NF-kappaB-positive cells were rare in HNL. Gene expression tree analysis of DNA microarrays showed different clustering of HNL and NSL. In comparison with NSL, HNL exhibited diffuse upregulation of these gene profiles, particularly of cyclins and caspases (ratio; cyclin A2, 2.72; caspase-6, 2.43; caspase-3, 2.02); whereas, Mcl-1, which has been shown to delay apoptosis, was downregulated (ratio, 0.71), as confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR). Almost all apoptosis-associated genes, especially caspases, were upregulated, and apoptosis inhibitory genes, including bcl-2 by immunohistochemistry, were downregulated in all five cases with HNL. In addition, cell cycle-associated genes were upregulated in all. These findings confirm that both apoptosis and proliferation are simultaneously present in HNL lesions.