Protective Effect of β‐Glucan Against Mycobacterium bovis, BCG Infection in BALB/c Mice

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Abstract
β‐1,3‐Glucan is a potent stimulator of macrophage functions and has a protective effect against a range of infections in rodent models. We examined whether the agent could also protect against the intracellular Mycobacterium bovis, bacillus Calmette–Guérin (BCG) infection in mice. BCG‐susceptible BALB/c mice were injected intravenously (i.v.) with β‐glucan or vehicle 3 days before, or with β‐glucan 7 days after i.v. challenge with live BCG bacilli. The animals were killed 4 or 8 weeks later, their organs were homogenized and applied to object slides and stained with auramin for counting of bacilli, or seeded onto agar in Petri dishes. Mice treated with β‐glucan both pre‐ and postchallenge had significantly lower numbers of BCG bacilli and BCG colony‐forming units in spleen homogenates compared with controls 4 weeks after challenge. A similar, but not statistically significant, tendency was observed in spleen homogenates from mice killed 8 weeks after challenge. In homogenates of liver and lungs there were similar findings, but less pronounced. There was a dose‐dependent effect of β‐glucan injected before BCG challenge on the number of BCG bacilli found in spleen and liver homogenates. In addition, antibody cross‐reactivity was demonstrated between M. tuberculosis cell wall and β‐glucan. The results suggest that β‐glucan has a protective effect against M. bovis, BCG infection in susceptible mice.