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 (10(2) 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.