Influence of immunomodulation on the development of Listeria monocytogenes infection in aged guinea pigs

We investigated the impact of immunomodulation on the development of listeriosis within an aged population of guinea pigs after an intragastric challenge with Listeria monocytogenes. Supplementation with vitamin E for 35 days significantly increased the level of cytotoxic T cells (CD8⁺), while treatment with cyclosporin A resulted in a 25% decrease of CD8⁺ T cells. In the animals receiving the low dose (10² CFU) of L. monocytogenes, 50% of the control-group animals became infected. Only 22% of animals receiving the orthomolecular dose of vitamin E became infected, whereas animals that were immunosuppressed had an infection rate of 89%. In the immunosuppressed group three animals (16%) developed listerial infection with a quantifiable bacterial level of 0.3-3 log CFU g^-1 of organ in the spleen and liver. In the high-dose study, the population of L. monocytogenes was consistently 1 log CFU g^-1 lower in the spleen or liver of the vitamin E-supplemented group, compared with the control and cyclosporin A-treated animals. At day 4, a significant increase in the levels of CD8 ⁺ during listerial infection occurred in vitamin E-supplemented animals, suggesting an increased ability to produce CD8⁺ T cells. The results suggest that immunomodulation of the host can influence listerial infection within an aged population of guinea pigs.