The activation of caspase-3 and DNA fragmentation in B cells phagocytosed by macrophages |
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Authors: | Eiji Ninomiya Yuko Ito Masa-Aki Shibata Keisei Kawashima Takeshi Sakamoto Eikun Maruyama Hisao Doi Kosuke Tokitsu Yoshinori Otsuki |
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Institution: | Department of Anatomy and Biology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka 569-8686, Japan. |
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Abstract: | Apoptotic signaling of mammalian cells involves two pathways: the death receptor and mitochondrial pathways. In this in vivo study, we investigated apoptotic signaling of B cells in mouse germinal centers (GCs) of gut-associated lymphoid tissues (GALTs) using transmission electron microscopy (TEM), terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL), immunofluorescence of members of caspase family and cFLIP(L), and caspase activity assay. It was very difficult to ultrastructurally differentiate B cells undergoing apoptosis from B cells differentiating into memory cells or plasma cells among B cells constituting GCs. Isolated B cells in GCs showed no active form of caspase-3 or TUNEL immunoreactivity, but expressed cFLIP(L). Contrary to isolated B cells, apoptotic B cells phagocytosed by macrophages exhibited immunoreactivity of the active form of caspase-3 and TUNEL, but lacked the cFLIP(L) expression. The caspase activity assay in GALTs clearly showed intense activity of caspase-3, caspase-9, and caspace-8 that was high in order. Therefore, the death receptor pathway accompanying the increased activity of caspase-3 and caspase-8 may be blocked by the expression of cFLIP(L) in B cells of GALTs. Moreover, both the activation of caspase-3 and DNA fragmentation first occur only when B cells are phagocytosed by macrophages. |
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