Abstract
Summary
To determine if the resistance to intracellular bacteria observed in mice chronically infected with Toxoplasma gondii or Besnoitia jellisoni extends also against viruses, mice infected with these protozoa were challenged with Mengo virus. Significantly greater survival and/or prolonged time to death were noted in the protozoal infected animals when compared with controls. This resistance to viral challenge persisted in some groups of mice for longer than 1 year. Resistance to viral challenge was also noted in mice infected with Listeria monocytogenes but less marked and persisted for a shorter period of time than in protozoal-infected animals. To define a possible role for interferon, serum, peritoneal fluid, and spleens of the protozoal-infected mice were assayed for interferon levels at various intervals following initial infection. Interferon was demonstrable only during the acute stage of the infections, whereas resistance to viral challenge in the same animals persisted in some instances for more than 1 year. Freund's complete adjuvant also conferred resistance to Mengo virus for a period of 5 months. The role of persistent active infection and of humoral and cellular mechanisms as well as of interferon in the observed resistance are discussed.
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