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  • Title: Apoptosis by neglect of CD4+ Th cells in granulomas: a novel effector mechanism involved in the control of egg-induced immunopathology in murine schistosomiasis.
    Author: Rutitzky LI, Mirkin GA, Stadecker MJ.
    Journal: J Immunol; 2003 Aug 15; 171(4):1859-67. PubMed ID: 12902487.
    Abstract:
    In infection with Schistosoma mansoni, parasite eggs precipitate an intrahepatic granulomatous and fibrosing inflammation that is mediated by CD4(+) Th cells. Compared with CBA mice, C57BL/6 mice develop smaller granulomas composed of cells that exhibit reduced proliferative responses to schistosome egg Ags. In the present study, we investigated CD4(+) T cell apoptosis as a possible mechanism that could account for this subdued response. We found throughout the course of several infection weeks a markedly higher proportion of apoptotic CD4(+) T cells in granulomas from C57BL/6 mice than in those from CBA mice ex vivo; the apoptosis further increased upon cell cultivation in vitro. Activation-induced cell death or CD8(+) T cells failed to account for the enhanced apoptosis as infected Fas-, Fas ligand,- and CD8-deficient mice exhibited similar apoptosis to that seen in wild-type counterparts. However, a strikingly lower IL-2 production by schistosome egg Ag-stimulated C57BL/6 granuloma and mesenteric lymph node cells suggested the possibility of apoptosis due to growth factor deprivation. Indeed, the CD4(+) T cell apoptosis was significantly reversed by addition of rIL-2 in vitro, or by injection of rIL-2 in vivo, which also resulted in significant exacerbation of granulomatous inflammation. These findings indicate that apoptosis by neglect can represent a significant means of controlling CD4(+) T cells that mediate the immunopathology in schistosomiasis.
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