A cysteine protease from Taenia solium metacestodes induce apoptosis in human CD4+ T-cells

Here we investigated whether the depletion of CD4+ lymphocytes, observed in mononuclear cells incubated with Taenia solium metacestode E/S products or with living cysts was due to apoptosis. Using the deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL), electron microscopy and DNA gel electrophoresis, we found signs of apoptosis in these cells. Results showed that cysteine protease activity was responsible for this effect, since E-64 prevented cell death in all cases. Electron microscopy studies showed that lymphocytes exhibited features of apoptosis such as cellular membrane integrity, strangling and fragmentation of nuclei, chromatin condensation, apoptotic bodies and loss of microvilli. In contrast, lymphocytes co-cultured with living metacestodes plus E-64 exhibited integrity of their structures. DNA fragmentation was detected by TUNEL assays and DNA gel electrophoresis. The results suggested that cell death induced by the cysteine protease from the T. solium metacestode may be involved in down-regulation of cell-mediated responses in infected hosts.