Resistance to infection and activation of the monocyto-macrophage system caused by Bacillus firmus and its fractions

The hepatocyte as a microbial product-responsive cell

Much research has focused on the responses to microbial products of immune cells such as monocytes, macrophages, and neutrophils. Although the liver is a primary response organ in various infections, relatively little is known about the antimicrobial responses of its major cell type, the hepatocyte. It is now known that the recognition of bacteria occurs via cell-surface proteins that are members of the Toll-like receptor (TLR) family. In addition, lipopolysaccharide (LPS) is bound by circulating LPS-binding protein (LBP) and presented to cell-surface CD14, which in turn interacts with TLR and transduces an intracellular signal. We investigated the CD14 and TLR2 responses of whole liver and isolated hepatocytes, and demonstrated that these cells can be induced to express the molecules necessary for responses to both Gram-positive and Gram-negative bacteria. Our findings may have clinical implications for pathological states such as sepsis.

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.

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

Intranasal immunization of guinea pigs with inactivated type B influenza virus plus inactivated Bacillus firmus as an adjuvant compared to the virus alone yields higher titers of serum hemagglutination-inhibiting antibodies and virus-neutralizing antibodies. This phenomenon could be useful in standard serology, especially in the preparation of immune sera against highly pathogenic strains for in vitro diagnosis.

Immune response after adjuvant mucosal immunization of mice with inactivated influenza virus

Satisfactory mucosal immunity in the respiratory tract is very important for protection against influenza. It can be achieved only by mucosal immunization. Mucosal vaccination with inactivated influenza virus may not be sufficiently effective and suitable adjuvants are therefore sought. We tested intratracheal immunization of mice with inactivate B type influenza virus in a mixture with formolized G+ bacterium Bacillus firmus, whose adjuvant effects have previously been documented in another system. The treatment resulted in a marked increase of both systemic and mucosal antibody response in IgG and IgA classes. Stimulation of T lymphocytes after adjuvant immunization was very mild, no proliferation taking place after specific stimulation with antigen in vitro. However, slightly increased systemic (spleen) and local (lungs) production of cytokines without perceptible Th1/Th2 polarization was determined. B. firmus is an efficient adjuvant in respiratory tract immunization while with subcutaneous immunization it lowers the antibody response.

Immunostimulatory effect of Bacillus firmus on mouse lymphocytes

Bacillus firmus (a Gram-positive nonpathogenic and harmless bacterium), was shown to be a strong polyclonal activator of mouse B lymphocytes as estimated by ELISA testing of Ig concentrations in culture supernatants after incubation of BALB/c mouse splenocytes with inactivated bacillus. Synthesis of all main Ig classes and all IgG subclasses was stimulated in vitro, the considerable effect on IgA formation being the most interesting feature. B cell stimulation was T cell dependent, as was demonstrated by the effect of B. firmus on all Ig isotypes and by comparison of lymphocyte response of nu/nu mice and heterozygous nu/+ mice. The effect of B. firmus on splenocyte proliferation was stimulatory or suppressive depending on the dose of the bacterium. Increased synthesis of IFN-gamma and IL-10 (detected by ELISA in splenocyte culture supernatants) showed probable stimulation of Th1 and Th2 subpopulations. Considering the stimulatory effect on IgA formation and macrophage stimulation, B. firmus seems to be a prospective mucosal adjuvant and/or probiotic.

Differential effect of Bacillus firmus on immune response and enterocyte brush-border enzyme levels in BALB/c and B10.BR mice

A nonpathogenic bacterium of external environment possessing remarkable immunomodulatory activity, Bacillus firmus (BF) inactivated with formaldehyde, was given intragastrically to two genetically different mouse strains BALB/c (H-2d) and B10.BR/SnPh (B10.BR, H-2k) reared in conventional (CV) and B10.BR strain also in germ-free (GF) conditions. Repeated intragastric administration of BF (500 micrograms every other day over two weeks, starting at the age of 3 months) significantly enhanced intestinal IgA levels in CV BALB/c mice but did not affect intestinal IgA in CV B10.BR mice. In GF B10.BR mice, IgG levels in sera and intestinal washings increased after BF administration compared to CV B10.BR mice. In CV BALB/c mice, specific activity of enterocyte brush-border enzymes (lactase, gamma-glutamyltransferase, alkaline phosphatase) decreased after BF treatment; sucrase (sucrose alpha-glucosidase) activity was not affected. On the other hand, in B10.BR mice, specific activity of gamma-glutamyltransferase and dipeptidyl peptidase IV were higher after administration of BF in both CV and GF groups relative to untreated controls. The activities of lactase and glucoamylase (glucan 1,4-alpha-glucosidase) were significantly stimulated only in the group of GF B10.BR mice treated with formolized BF. The stimulation of immunoglobulin production after BF treatment was accompanied by changes in the levels of enterocyte brush-border enzymes; this responsiveness to BF treatment was genetically regulated.

Effect of Bacillus firmus on antibody formation after mucosal and parenteral immunization in mice

Immunostimulatory properties of B. firmus, a nontoxic, nonpathogenic G + bacterium of external environment, were described previously. Antiinfectious and antitumor activity, macrophage activation and strong polyclonal stimulation of B lymphocytes were proved in human, mice and rats. The adjuvant effect of B. firmus on specific antibody response to ovalbumin in BALB/c mice is the topic of the present study. Against our expectation, B. firmus exerts more suppressive than stimulatory effect on specific antibody response. Formolized B. firmus decreased anti-ovalbumin response after subcutaneous immunization and only slightly increased serum antibodies after intraperitoneal immunization. After mucosal immunization, both oral and rectal, ovalbumin itself did not cause a significant systemic response but induced IgA anti-ovalbumin response in the intestine. B. firmus applied together with ovalbumin increased systemic serum response but absolutely eliminated intestinal response. The rectal route of antigen administration has been found less convenient because of less precise dosing of antigen in this mode of immunization.

Immunomodulatory effects of Bacillus firmus

3-day-old miniature piglets were stimulated in vivo with Bacillus firmus by the intraperitoneal or intragastric route for 1 d. Cells containing IgA and IgG2 were detected in the ileum in all stimulated but not in control animals. The frequency of blood CD3+ cells increased after intraperitoneal administration of B. firmus, the ratio of polymorphonuclears to lymphocytes increased in all stimulated piglets. B. firmus induced antitumor immunity in rats with transplanted Yoshida sarcoma cells. Granular lymphocytes and dead tumor cells were found in peritoneal exudate of stimulated animals. B. firmus induced IFN-gamma synthesis in human blood lymphocytes stimulated in vitro for 1 d. The amount of TNF-alpha produced by these stimulated human peripheral blood mononuclears (PBMC) was lower than that of PBMC stimulated with some other bacterial immunomodulators. Cells containing TGF-beta or IL-8 were not found in human PBMC stimulated with B. firmus.

Polyclonal activation of human lymphocytes by Bacillus firmus and its constituents

Bacillus firmus strongly stimulates Ig synthesis in the cultures of human peripheral blood mononuclear leukocytes. As apparent from the character of Ig formation and blastic transformation, the stimulation has features of a polyclonal activation of B lymphocytes without substantial participation of T lymphocytes. B firmus is a strong B cell polyclonal activator even for human cord blood lymphocytes. The most striking feature is the strong stimulation of IgA synthesis in both adult and cord blood lymphocytes. Several crude fractions were isolated from B. firmus. None of them exhibited any remarkable enhancement of activity but the cytoplasmic fraction P-40 was clearly more potent than the intact bacilli. On the other hand, cell wall peptidoglycan, a well known polyclonal activator of B cells, had a much lower activity than whole bacteria. The effect of B. firmus on the stimulation of Ig formation is thus relatively complex; it is not caused mainly by peptidoglycan but rather by some cytoplasmic constituents of the bacterium.

Prolonged survival of AVN Wistar rats with transplanted Yoshida sarcoma and increase of granular lymphocytes after administration of Bacillus firmus and their crude lipids

Bacillus firmus is a Gram-positive, aerobic, sporulating, nonpathogenic air contaminant which, according to earlier findings, is a strong polyclonal activator of B lymphocytes. The crude lipids of this microbe induced significant resistance of mice against listerial infection. The administration of bacterin, like that of crude lipids obtained by the extraction of cell suspension with chloroform-methanol to rats, strain AVN Wistar, transplanted later with Yoshida sarcoma, significantly prolonged the survival of the animals in comparison with the control group. At the same time the number of granular lymphocytes was increased. The destruction of tumor cells in the peritoneal exudate of immunostimulated rats was also determined.