Glucan as an adjuvant for a murine Babesia microti immunization trial

A vaccination protocol against murine Babesia microti infection, using glucan, a β-1,3-glucopyranose derivative of yeast cell walls, and glutaraldehyde-fixed infected erythrocytes was evaluated. BALB/c mice were immunized intravenously four times at 2-day intervals with 2 x 10⁸ fixed infected erythrocytes with and without glucan (0.45 mg). The mice were challenged 2 weeks after the last immunization with 10⁸ viable infected erythrocytes. Peak parasitemia was significantly reduced (8.9 ± 1.0%; P < 0.001) in glucan-immunized mice as compared with nonimmunized controls (41.2 ± 1.4%), glucan-treated controls (31.7 ± 2.5%; P < 0.05), or mice which received fixed infected erythrocytes without glucan (21.0 ± 1.2%; P < 0.01). Humoral and cellular immunity to B. microti was evaluated before challenge by measuring antibody titers and splenocyte blastogenic responses to B. microti antigens. The in vitro cellular response was inversely correlated with mean peak parasitemia (P < 0.05). These observations demonstrate that glucan is an effective adjuvant in enhancing immunity to murine babesiosis.