Glucan-induced enhancement of host resistance to selected infectious diseases.

We conducted studies with mice, rats, and monkeys which demonstrated the ability of glucan to induce either nonspecific or specific enhancement of host resistance to infectious diseases. Intravenous pretreatment of mice with glucan significantly enhanced the survival of mice challenged with either Venezuelan equine encephalomyelitis (VEE) virus or Rift Valley fever virus. Pretreatment was beneficial when initiated 3 days before challenge with VEE virus and 7 days before challenge with Rift Valley fever virus. Treatment of mice after VEE challenge did not increase their survival compared with controls. Glucan pretreatment of rats provided increased resistance to both intraperitoneal and low-dose aerosol challenges with virulent Francisella tularensis when the glucan was given intravenously, but not when it was administered intranasally. In contrast, intranasal glucan pretreatment enhanced the survival of mice when they were challenged by aerosol with Pseudomonas pseudomallei, whereas intravenous glucan pretreatment did not increase survival. mice given glucan combined with a marginally immunogenic dose of VEE vaccine were more resistant to homologous virus challenge than were mice given either Freund complete adjuvant plus vaccine or vaccine alone. Similarly, both primary and secondary VEE antibody titers in cynomolgus monkeys given glucan with VEE vaccine were significantly greater than titers in vaccine controls.