Adjuvant effect ofBacillus firmus in intranasal immunization of guinea pigs with inactivated type B influenza virus

Immunomodulatory properties of subcellular fractions of a G+ bacterium, Bacillus firmus

Mucosal immunization with non-living antigens usually requires the use of an adjuvant. The adjuvant activity of Bacillus firmus in the mucosal immunization of mice was described by our laboratory previously. In the present study, subcellular localization of B. firmus activities was followed. After mechanical disintegration, subcellular components of bacterium were fractionated by differential centrifugation and salting out. Bacterial cell walls, cytoplasmic membrane fraction, soluble cytoplasmic proteins, and ribosomal fractions were isolated. Their effect on the mouse immune system was studied. Lymphocyte proliferation and immunoglobulin formation in vitro were stimulated by bacterial cell wall (BCW), cytoplasmic membrane (CMF), and ribosomal fractions. BCW and CMF increased antibody formation after intratracheal immunization of mice with influenza A and B viruses, and increased protection against subsequent infection with influenza virus. The BCW fraction even induced intersubtypic cross-protection: Mice immunized with A/California/7/04 (H3N2) + BCW were resistant to the infection by the highly pathogenic A/PR/8/34 (H1N1) virus.

Immunomodulatory effects ofBacillus firmus on mouse peritoneal cellsin Vitro

The effect of nonpathogenic G+ bacterium B. firmus (BF) on stimulation of mouse peritoneal cells in vitro was evaluated by testing nitric-oxide-synthesis induction and cytokine formation. The reactivity was compared of peritoneal cells from two inbred mouse strains, C57B1/6 and BALB/c, which differ in their immunological reactivity. Peritoneal macrophages from C57B1/6 produced more nitric oxide after a 1-d cultivation with inactivated BF than those of BALB/c mice. In both strains, production can be further increased by adding exogenous IFN-gamma to the culture. There were no significant differences between peritoneal cells of these two mouse strains in cytokine production after optimal in vitro stimulation with BF. BF effectively activated peritoneal cells for the production of TNF-alpha, IL-1beta and IL-10, delipidated bacterium (DBF) being more efficient than BF in induction of IL-10 and TNF-alpha. On the other hand, BF had only small effect on IFN-gamma production and no detectable effect on IL-12 production. Macrophage activation by BF/DBF can represent one of the mechanisms responsible for previously described immunomodulatory activity of BF.