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In the current research, we report apoptosis of lymphocytes in the inflammatory reaction around metacestodes in muscle tissue from cysticercotic pigs. Two events, high metacestode viability (100%) and high cysteine protease activity were found to be closely related to a high phosphatydilserine expression by inflammatory lymphocytes (56%). Testing the RPMI medium used for washing away inflammatory cells from metacestodes with 100% viability, with the fluorescent substrate Z-Phe-Ala-AFC for measuring cysteine protease activity, significant fluorescent values were found. In contrast, tests performed with RPMI medium used for washing away inflammatory cells from metacestodes with 90% viability or less, showed low fluorescence values. Flow cytometry analyses of inflammatory cells obtained from four naturally cysticercotic pigs, and stained with Annexin-V/PI, showed lymphocytes expressing phosphatidylserine with values of 0, 6, 41 and 56% on their outer surfaces. Electron microscopy studies of inflammatory cells from metacestodes with 100% viability, showed lymphocytes with strangled and fragmented nuclei, and heterochromatin displaced to the nuclear periphery. In addition, DNA from these cells showed fragmentation in electrophoresis assays. Apoptosis of lymphocytes in the inflammatory reaction around Taenia solium metacestodes, might have been induced by the parasite cysteine protease, and may be involved in impairing cell-mediated immune responses in human and porcine cysticercosis.

To assess the immunological status of mice parasitized with Taenia crassiceps metacestodes, 6-month old female BALB/c mice experimentally parasitized with T. crassiceps and immunized with Salmonella typhimurium antigens were infected with S. typhimurium virulent bacilli (1.6 x LD50). Both T. crassiceps-parasitized and immunized and parasitized mice showed a very high susceptibility to infection (**P < 0.01) with higher bacteremia than control and immunized-control animals and produced a reduced IgG response to S. typhimurium, antigens (* P < 0.05). This indicates that T. crassiceps is able to preclude development of immunity to S. typhimurium, because appropriate antibody production to a heterologous antigenic stimulus did not take place, and the bacteremia results suggest the parasitosis altered the mononuclear phagocyte system. It has been demonstrated that Taenia solium metacestodes produce a small RNA molecule in culture which suppresses humoral and cellular responses against homologous antigens in mice. We propose that T. crassiceps may be actively synthesizing such a factor, apart from other simultaneously acting immunomodulatory mechanisms, to induce an immunosuppressed state favorable to its development in the host.

It has previously been demonstrated that immunization of pigs with a crude extract of Taenia solium metacestodes can confer a high level of protection against an egg challenge. Furthermore, vaccination of infected animals also induces an immune response against the larvae, which are either destroyed or rendered non-infectious. To assess the efficacy of immunization as a strategy for reducing the prevalence of porcine cysticercosis, a field trial of this vaccine was performed in an endemic area in the northern region of the Guerrero State, Mexico, Random samples of pigs belonging to 17 villages were examined for metacestodes by inspection of their tongues. Each animal was immunized with a dose of 150 micrograms of protein (antigenic extract from Taenia solium metacestodes) by the intramuscular route. A prevalence of 2.4% of porcine cysticercosis on average was found in these villages at the beginning of the trial (62 cysticercotic pigs out of 2650 inspected). Six of these villages were selected for the periodic vaccination of new random samples of pigs. A statistically significant decline in the prevalence of porcine cysticercosis was observed at the end of the trial, decreasing from 2.4% at the beginning of vaccination to 0.45% at the end of the trial. A reduction of 82% was observed in spite of the poor living conditions in these villages. These results are consistent with previous data and suggest that it may be possible to turn a susceptible pig population into a protected one by systematic vaccination.

In chronic helminthic infections such as cysticercosis, where the parasites live for years, profound modulation of the host immune response has been reported. To evaluate the genotoxicity of a drug used to treat cysticercosis, we observed the occurrence of genetic damage in cultured lymphocytes from cysticercotic swine and patients who had not been exposed to the drug. The human lymphocytes also showed a slower proliferation. These data suggested that the disease itself was promoting genetic damage in host lymphocytes which, in part, could explain the retardation of the lymphocyte proliferation observed in cysticercotic patients. Pigs infected with Taenia solium cysticerci showed an increased lymphocyte proliferation for 6-8 weeks post infection, followed by an impaired proliferation after this period. Significant induction of sister-chromatid exchanges was also observed in lymphocytes from infected pigs after the 6th week post infection. Additionally, it was found that a factor secreted by the cysticerci morphologically transformed primary fibroblasts in culture. The results strongly suggest that the parasite produces genetic instability in the host cells, which could result in immunosuppression and malignant transformation of target cells.