ENTAMOEBA-HISTOLYTICA - TARGET-CELLS KILLED BY TROPHOZOITES UNDERGO DNA FRAGMENTATION WHICH IS NOT BLOCKED BY BCL-2

Amebic destruction of neutrophils and macrophages is contact-dependent . Adherence is mediated by a galactose-specific surface lectin on the amebic membrane. The pathway by which contact-dependent cytolysis of t he target cell occurs is unknown. We hypothesized that target cell dea th is due to the triggering of apoptosis (programmed cell death) by th e amebae. The purpose of this study was to determine whether target ce ll DNA is fragmented into a ladder pattern characteristic of apoptosis and to test whether overexpression of Bcl-2, a protein that confers r esistance to apoptotic death from some stimuli, blocks target cell kil ling. The murine myeloid cell line FDC-P1 transfected with a retroviru s construct expressing the Bcl-2 protein was shown to be resistant to the apoptotic death that the parental line undergoes upon growth facto r deprivation. Cr-51-labeled FDC-P1 control or bcl-2-transfected cells were incubated with Entamoeba histolytica (4:1 cell/ameba ratio) and killing of the cells was assessed by Cr-51 release. Both cell lines we re susceptible to contact-dependent killing. Death induced by the ameb ae in the bcl-2-transfected cells resulted in a DNA ladder fragmentati on pattern (using [I-125]iododeoxyuridine-labeled target cell DNA) ide ntical to that seen in the control cells undergoing apoptosis upon gro wth factor withdrawal. Target cell DNA fragmentation was inhibited by blocking adherence with galactose. Our data suggest that target cell k illing by E. histolytica can occur via Bcl-2-independent apoptotic mec hanism. (C) 1994 Academic Press, Inc.