Tumor necrosis factor-alpha mediates RANK ligand stimulation of osteoclast differentiation by an autocrine mechanism

Osteoblasts or bone marrow stromal cells are required as supporting cells for the in vitro differentiation of osteoclasts from their progenitor cells. Soluble receptor activator of nuclear factor-kappaB ligand (RANKL) in the presence of macrophage colony-stimulating factor (M-CSF) is capable of replacing the supporting cells in promoting osteoclastogenesis. In the present study, using Balb/c-derived cultures, osteoclast formation in both systems-osteoblast/bone-marrow cell co-cultures and in RANKL-induced osteoclastogenesis-was inhibited by antibody to tumor necrosis factor-alpha (TNF-alpha), and was enhanced by the addition of this cytokine. TNF-alpha itself promoted osteoclastogenesis in the presence of M-CSF. However, even at high concentrations of TNF-alpha the efficiency of this activity was much lower than the osteoclastogenic activity of RANKL. RANKL increased the level of TNF-alpha mRNA and induced TNF-alpha release from osteoclast progenitors. Furthermore, antibody to p55 TNF-alpha receptors (TNF receptors-1) (but not to p75 TNF-alpha receptors (TNF receptors-2) inhibited effectively RANKL- (and TNF-alpha() induced osteoclastogenesis. Anti-TNF receptors-1 antibody failed to inhibit osteoclastogenesis in C57BL/6-derived cultures. Taken together, our data support the hypothesis that in Balb/c, but not in C57BL/6 (strains known to differ in inflammatory responses and cytokine modulation), TNF-alpha is an autocrine factor in osteoclasts, promoting their differentiation, and mediates, at least in part, RANKL's induction of osteoclastogenesis.     

Interleukin (IL)-12 mediates the anti-osteoclastogenic activity of CpG-oligodeoxynucleotides

Bacterial DNA activates the innate immune system via interactions with Toll-like receptor 9 (TLR9). This receptor recognizes CpG-oligodeoxynucleotides (CpG-ODNs) mimicking the CpG dinucleotides in certain sequence contexts characterizing this DNA. Most studies have shown increased osteoclast differentiation by TLR ligands. We found that activation of TLRs (specifically TLR4 and TLR9) in early osteoclast precursors results in inhibition of receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast differentiation. Our objective is to identify the mechanism leading to this inhibitory effect of a TLR ligand. Since both RANKL-RANK and CpG-ODN-TLR9 interactions result in NF-kappaB activation, p38 and ERK phosphorylation, and TNF-alpha synthesis (all implicated in osteoclastogenesis), we hypothesized that CpG-ODN (but not RANKL) in addition induces the synthesis of an anti-osteoclastogenic factor. Control osteoclast precursors, and cells treated with RANKL, CpG-ODN, or their combination were studied using DNA arrays (GEArray Q Series Mouse NF-kappaB Signaling Pathway Gene Array, MM-016, SuperArray). We found a marked increase in the mRNA levels of the osteoclastogenesis inhibitor interleukin-12 (IL-12) in osteoclast precursors treated with CpG-ODN and CpG-ODN + RANKL. Northern and Western analyses, together with ELISA, confirmed the DNA array studies. In correlation with these findings, IL-12 inhibited RANKL-induced osteoclast differentiation and specific anti-IL-12-antibodies inhibited the anti-osteoclastogenic effect of CpG-ODN. In conclusion, activation of TLR9 by its ligand, CpG-ODN, results in synthesis and release of IL-12 opposing RANKL-induced osteoclast differentiation.     

Akt is a neutral amplifier for Th cell differentiation

Both CD28 and its relative, inducible costimulator (ICOS), have a binding motif for phosphatidylinositol 3-kinase (PI3K) in their cytoplasmic tail, and the binding of PI3K leads to activation of a serine/threonine kinase, Akt. The role of Akt in cytokine production and helper T (Th) cell differentiation remains obscure. In this study, we found that enforced expression of the constitutively active form (E40K) of Akt rendered CD4(+) T cells activated. Wild-type of Akt and E40K promoted Th1 cell differentiation in C57BL/6-derived and Th1-polarized BALB/c-derived CD4(+) T cells, while both promoted Th2 cell differentiation in BALB/c-derived and Th2-polarized C57BL/6 CD4(+) T cells. E40K also facilitated Th1 differentiation in CD4(+) T cells from IL-4-deficient mice with the BALB/c background. E40K up-regulated expression of NF-AT and c-Myb, which may be related to the augmentation of cytokine production by E40K. These findings indicate that the mechanism by which Akt augments cytokine production via CD28 and ICOS is Th cell type-specific and reflects the intracellular status affected by the cytokine milieu. We conclude that Akt is a neutral amplifier of T cell activation and Th differentiation.     

Anthrax lethal toxin-mediated killing of human and murine dendritic cells impairs the adaptive immune response

Many pathogens have acquired strategies to combat the immune response. Bacillus anthracis interferes with host defenses by releasing anthrax lethal toxin (LT), which inactivates mitogen-activated protein kinase pathways, rendering dendritic cells (DCs) and T lymphocytes nonresponsive to immune stimulation. However, these cell types are considered resistant to killing by LT. Here we show that LT kills primary human DCs in vitro, and murine DCs in vitro and in vivo. Kinetics of LT-mediated killing of murine DCs, as well as cell death pathways induced, were dependent upon genetic background: LT triggered rapid necrosis in BALB/c-derived DCs, and slow apoptosis in C57BL/6-derived DCs. This is consistent with rapid and slow killing of LT-injected BALB/c and C57BL/6 mice, respectively. We present evidence that anthrax LT impairs adaptive immunity by specifically targeting DCs. This may represent an immune-evasion strategy of the bacterium, and contribute to anthrax disease progression. We also established that genetic background determines whether apoptosis or necrosis is induced by LT. Finally, killing of C57BL/6-derived DCs by LT mirrors that of human DCs, suggesting that C57BL/6 DCs represent a better model system for human anthrax than the prototypical BALB/c macrophages.     

The synthetic analogue of mycoplasmal lipoprotein FSL-1 induces dendritic cell maturation through Toll-like receptor 2

Granulocyte-macrophage colony-stimulating factor-differentiated bone marrow-derived dendritic cells were stimulated with the synthetic lipopeptide S-(2,3-bispalmitoyloxypropyl)-CGDPKHSPKSF (FSL-1) or the Escherichia coli lipopolysaccharide. FSL-1 induced the production of TNF-alpha and IL-12 by C57BL/6-derived bone marrow-derived dendritic cells but not by bone marrow-derived dendritic cells from Toll-like receptor 2-deficient (TLR2(-/-)) mice. Lipopolysaccharide induced the production of TNF-alpha and IL-12 by bone marrow-derived dendritic cells derived from either type of mice. FSL-1 did not induce production of IL-10 by bone marrow-derived dendritic cells from either type of mice, whereas lipopolysaccharide induced small amounts of IL-10 by bone marrow-derived dendritic cells from both types of mice. The upregulation by FSL-1 of the expression of CD80, CD86 and the MHC class II molecule IA(b) was dose- and time-dependent on the surfaces of C57BL/6-derived bone marrow-derived dendritic cells but not on the surface of TLR2(-/-)-derived bone marrow-derived dendritic cells. Lipopolysaccharide upregulated the expression of these molecules on the surfaces of bone marrow-derived dendritic cells from both types of mice. The expression of CD11c on the surfaces of C57BL/6-derived bone marrow-derived dendritic cells was upregulated by stimulation with both FSL-1 and lipopolysaccharide up to 12 h; thereafter, the expression was downregulated. The results suggest that FSL-1 can accelerate maturation of bone marrow-derived dendritic cells and this FSL-1 activity is mediated by TLR2.     

Distinct osteoclast precursors in the bone marrow and extramedullary organs characterized by responsiveness to Toll-like receptor ligands and TNF-alpha

Osteoclasts are derived from hemopoietic stem cells and play critical roles in bone resorption and remodeling. Multinucleated osteoclasts are attached tightly to bone matrix, whereas precursor cells with the potential to differentiate into osteoclasts in culture are widely distributed. In this study, we assessed the characteristics of osteoclast precursors in bone marrow (BM) and in extramedullary organs as indicated by their responsiveness to ligands for Toll-like receptors (TLRs) and to TNF-alpha. Development of osteoclasts from precursor cells in the BM was inhibited by CpG oligonucleotides, a ligand for TLR9, but not by LPS, a ligand for TLR4. BM osteoclasts were induced by TNF-alpha as well as receptor activator of NF-kappaB ligand in the presence of M-CSF. Splenic osteoclast precursors, even in osteoclast-deficient osteopetrotic mice, differentiated into mature osteoclasts following exposure to TNF-alpha or receptor activator of NF-kappaB ligand. However, splenic osteoclastogenesis was inhibited by both LPS and CpG. Osteoclastogenesis from peritoneal precursors was inhibited by not only these TLR ligands but also TNF-alpha. The effects of peptidoglycan, a ligand for TLR2, were similar to those of LPS. BM cells precultured with M-CSF were characterized with intermediate characteristics between those of splenic and peritoneal cavity precursors. Taken together, these findings demonstrate that osteoclast precursors are not identical in the tissues examined. To address the question of why mature osteoclasts occur only in association with bone, we may characterize not only the microenvironment for osteoclastogenesis, but also the osteoclast precursor itself in intramedullary and extramedullary tissues.     

Marrow stromal cells and osteoclast precursors differentially contribute to TNF-alpha-induced osteoclastogenesis in vivo

The marrow stromal cell is the principal source of the key osteoclastogenic cytokine receptor activator of NF-kappaB (RANK) ligand (RANKL). To individualize the role of marrow stromal cells in varying states of TNF-alpha-driven osteoclast formation in vivo, we generated chimeric mice in which wild-type (WT) marrow, immunodepleted of T cells and stromal cells, is transplanted into lethally irradiated mice deleted of both the p55 and p75 TNFR. As control, similarly treated WT marrow was transplanted into WT mice. Each group was administered increasing doses of TNF-alpha. Exposure to high-dose cytokine ex vivo induces exuberant osteoclastogenesis irrespective of in vivo TNF-alpha treatment or whether the recipient animals possess TNF-alpha-responsive stromal cells. In contrast, the osteoclastogenic capacity of marrow treated with lower-dose TNF-alpha requires priming by TNFR-bearing stromal cells in vivo. Importantly, the osteoclastogenic contribution of cytokine responsive stromal cells in vivo diminishes as the dose of TNF-alpha increases. In keeping with this conclusion, mice with severe inflammatory arthritis develop profound osteoclastogenesis and bone erosion independent of stromal cell expression of TNFR. The direct induction of osteoclast recruitment by TNF-alpha is characterized by enhanced RANK expression and sensitization of precursor cells to RANKL. Thus, osteolysis attending relatively modest elevations in ambient TNF-alpha depends upon responsive stromal cells. Alternatively, in states of severe periarticular inflammation, TNF-alpha may fully exert its bone erosive effects by directly promoting the differentiation of osteoclast precursors independent of cytokine-responsive stromal cells and T lymphocytes.     

Enhanced proinflammatory response to the Candida albicans gpi7 null mutant by murine cells

The Candida albicans gpi7/gpi7 null mutant strain (Deltagpi7), which is affected in glycosylphosphatidylinositol (GPI) anchor biosynthesis, showed a reduced virulence following systemic infection of C57BL/6 mice. In vitro production of TNF-alpha, IL-6 and IL-1beta by macrophages in response to Deltagpi7 cells was significantly increased as compared to control (wild type GPI7/GPI7 and revertant gpi7/GPI7) cells; this probably contributes to the enhanced recruitment of neutrophils to the peritoneal cavity in response to Deltagpi7 cells. Survival of knockout mice for Toll-like receptor (TLR) 2 and TLR4 following intravenous injection of Deltagpi7 cells showed no significant differences as compared to C57BL/6 mice. In vitro production of TNF-alpha by macrophages and neutrophil recruitment were significantly inhibited in TLR2-/- mice in response to control yeast strains. Interestingly both TNF-alpha production and neutrophil recruitment in response to Deltagpi7 were significantly increased in all three types of mice, with no differences among them, and laminarin failed to inhibit this increased production of TNF-alpha. These results indicate that the enhanced proinflammatory response to Deltagpi7 does not involve recognition through TLR2, TLR4 nor dectin-1. Therefore, complete GPI anchors confer surface properties that are involved in modulation of cytokine production by macrophages in response to C. albicans.     

An X-encoded alloantigenicity between BALB/c and C57BL/6 strains of mice

To detect minor barriers to histocompatibility that might be encoded on the X chromosome in mice, we grafted reciprocal sets of (C57BL/6xBALB/c)F1, (C57BL/6xDBA/2)F1, and (BALB/cxDBA/2)F1 mice with tail skin from the respective paternal inbred strain. Our histogenic analysis suggests that, compared with the C57BL/6 mouse strain, the BALB/c strain generates X-linked antigen loss. In contrast, we detected no X-linked histogenic differences between strains C57BL/6 and DBA/2, or DBA/2 and BALB/c. To localize this X-linked barrier to histocompatibility, we produced a panel of 25 [(BALB/cxC57BL/6)F1xC57BL/6]N2 males that were grafted with C57BL/6 skin to determine which carried the BALB/c-derived component(s) necessary for graft rejection. DNA marker analysis showed one region of overlapping BALB/c-derived X-chromosomal segments among the graft rejecters, suggesting that this antigen-loss haplotype ( H-hix(c), for histoincompatibility on the X chromosome, c haplotype) may be restricted within the DXMit55 to the Xq telomere interval (which excludes only the centromeric tip of the X). Further backcrossing of H-hix(c) to C57BL/6 resulted in fewer rejecter mice than expected by the N4 generation, suggesting that a second, unlinked locus is also involved in this X-linked alloantigenicity. The vigorous rejection of male (C57BL/6xBALB)F1 and female (B6.C- H2(d)xC57BL/6)F1 skin by (BALB/cxC57BL/6)F1 males, as well as the assessment of markers on Chromosome 17 among N2 and N4 graft-recipient males, suggests that this second locus is H2, and that H-hix(b)-encoded alloantigens require both H2(b) and H2(d)-encoded presentation molecules for efficient graft rejection.     

Stimulation by toll-like receptors inhibits osteoclast differentiation

Osteoclasts, the cells capable of resorbing bone, are derived from hemopoietic precursor cells of monocyte-macrophage lineage. The same precursor cells can also give rise to macrophages and dendritic cells, which are essential for proper immune responses to various pathogens. Immune responses to microbial pathogens are often triggered because various microbial components induce the maturation and activation of immunoregulatory cells such as macrophages or dendritic cells by stimulating Toll-like receptors (TLRs). Since osteoclasts arise from the same precursors as macrophages, we tested whether TLRs play any role during osteoclast differentiation. We showed here that osteoclast precursors prepared from mouse bone marrow cells expressed all known murine TLRs (TLR1-TLR9). Moreover, various TLR ligands (e.g., peptidoglycan, poly(I:C) dsRNA, LPS, and CpG motif of unmethylated DNA, which act as ligands for TLR2, 3, 4, and 9, respectively) induced NF-kappa B activation and up-regulated TNF-alpha production in osteoclast precursor cells. Unexpectedly, however, TLR stimulation of osteoclast precursors by these microbial products strongly inhibited their differentiation into multinucleated, mature osteoclasts induced by TNF-related activation-induced cytokine. Rather, TLR stimulation maintained the phagocytic activity of osteoclast precursors in the presence of osteoclastogenic stimuli M-CSF and TNF-related activation-induced cytokine. Taken together, these results suggest that TLR stimulation of osteoclast precursors inhibits their differentiation into noninflammatory mature osteoclasts during microbial infection. This process favors immune responses and may be critical to prevent pathogenic effects of microbial invasion on bone.     

Mouse genotype affects inducible expression of cytokine genes.

The levels of circulating IFN in mice infected with Newcastle disease virus (NDV) are regulated by the If-1 locus. In this study we show that in NDV-infected C57BL/6 mice, which carry the If-1h allele and produce high levels of IFN, high levels of both IFN-alpha and -beta mRNA can be detected in the spleen. In contrast, only very low levels of IFN mRNA could be detected in spleens of infected BALB/c mice containing the If-1l allele and producing low levels of IFN or in B6.C-H28c mice that are congenic for the If-1l allele. The relative levels of all individual IFN-alpha 1, alpha 4, and alpha 6 mRNA in spleens of infected BALB/c were lower than in spleens of infected C57BL/6 mice, indicating that the If-1 locus affects the expression of all IFN-alpha subtypes and is not associated with the deletion or inactivation of a specific IFN gene. The relative levels of IFN regulatory factor-1 mRNA in infected mice carrying the If-1l and If-1h loci were comparable, suggesting that the If-1 regulation is not associated with the altered expression of the IFN regulatory factor-1 gene. Quantitative difference in the expression of IFN-alpha and -beta genes was also observed in in vitro-infected peritoneal macrophages isolated from either C57BL/6 or BALB/c mice. A surprise finding was that the If-1 locus also affected the NDV-induced expression of two other cytokine genes, TNF-alpha and IL-6. Priming of the macrophage cultures with murine IFN enhanced the expression of all cytokine genes, and the relative levels of IFN, TNF-alpha, and IL-6 mRNA induced by NDV in macrophages derived from C57BL/6 and BALB/c mice were comparable. We propose that the If-1 locus affects the early stages of a signal transduction pathway which are common to the virus-mediated induction of IFN, TNF-alpha, and IL-6 genes.     

Vaccination with the Leishmania major ribosomal proteins plus CpG oligodeoxynucleotides induces protection against experimental cutaneous leishmaniasis in mice

In the present work we analyze the antigenicity of Leishmania major ribosomal proteins (LRP) in infected BALB/c mice. We show that BALB/c mice vaccinated with LRP in the presence of CpG oligodeoxynucleotides (CpG-ODN) were protected against the development of dermal pathology and showed a reduction in the parasite load after challenge with L. major. This protection was associated with the induction of an IL-12 dependent specific-IFN-gamma response mediated mainly by CD4(+) T cell, albeit a minor contribution of CD8(+) T cells cannot be ruled out. Induction of Th1 responses against LRP also resulted in a reversion of the Th2 responses associated with susceptibility. A marked reduction of IgG1 antibody titer against parasite antigens besides an impaired IL-4 and IL-10 cytokine production by parasite specific T cells was observed. In addition, we show that the administration of the LRP plus CpG-ODN preparation also conferred protection in the naturally resistant C57BL/6 mice. In this strain protection was associated with a LRP specific IFN-gamma production in lymph nodes draining the challenge site. We believe that these evolutionary conserved proteins, combined with adjuvants that favor Th1 responses, may be relevant components of a pan-Leishmania vaccine.     

TLR ligands in the local treatment of established intracerebral murine gliomas

Local TLR stimulation is an attractive approach to induce antitumor immunity. In this study, we compared various TLR ligands for their ability to affect murine GL261 cells in vitro and to eradicate established intracerebral murine gliomas in vivo. Our data show that GL261 cells express TLR2, TLR3, and TLR4 and respond to the corresponding TLR ligands with increasing MHC class I expression and inducing IL-6 secretion in vitro, while TLR5, TLR7, and TLR9 are essentially absent. Remarkably, CpG-oligonucleotides (CpG-ODN, TLR9) appeared to inhibit GL261 cell proliferation in a cell-type specific, but CpG-motif and TLR9-independent manner. A single intratumoral injection of CpG-ODN most effectively inhibited glioma growth in vivo and cured 80% of glioma-bearing C57BL/6 mice. Intratumoral injection of Pam3Cys-SK4 (TLR1/2) or R848 (TLR7) also produced a significant survival benefit, whereas poly(I:C) (TLR3) or purified LPS (TLR4) stimulation alone was not effective. Additional studies using TLR9(+/+) wild-type and TLR9(-/-) knockout mice revealed that the efficacy of local CpG-ODN treatment in vivo required TLR9 expression on nontumor cells. Additional experiments demonstrated increased frequencies of tumor-infiltrating IFN-gamma producing CD4(+) and CD8(+) effector T cells and a marked increase in the ratio of CD4(+) effector T cells to CD4(+)FoxP3(+) regulatory T cells upon CpG-ODN treatment. Surviving CpG-ODN treated mice were also protected from a subsequent tumor challenge without further addition of CpG-ODN. In summary, this study underlines the potency of local TLR treatment in antiglioma therapy and demonstrates that local CpG-ODN treatment most effectively restores antitumor immunity in a therapeutic murine glioma model.     

The protocol for the isolation and cryopreservation of osteoclast precursors from mouse bone marrow and spleen

Osteoclasts are responsible for physiological bone remodeling as well as pathological bone destruction in osteoporosis, periodontitis and rheumatoid arthritis, and thus represent a pharmacological target for drug development. We aimed to characterize and compare the cytokine-induced osteoclastogenesis of bone marrow and spleen precursors. Established protocols used to generate osteoclasts from bone marrow were modified to examine osteoclastogenesis of the spleen cells of healthy mice. Osteoclast formation was successfully induced from spleen precursors using receptor activator of nuclear factor κB ligand (50 ng/ml) and macrophage colony stimulating factor (50 ng/ml). Compared to bone marrow cultures, differentiation from spleen required a longer cultivation time (9 days for spleen, as compared to 5 days for marrow cultures) and a higher plating density of non-adherent cells (75,000/cm² for spleen, as compared to 50,000/cm² for bone marrow). Osteoclasts generated from spleen precursors expressed osteoclast marker genes calcitonin receptor, cathepsin K and matrix metalloproteinase 9 and were capable of resorbing hydroxyapatite. The differentiation capacity of spleen and bone marrow precursors was comparable for BALB/c, C57BL/6 and FVB mice. We also developed and tested a cryopreservation protocol for the osteoclast precursors. While 70–80 % of cells were lost during the first week of freezing, during the subsequent 5 weeks the losses were within 2–5 % per week. Osteoclastogenesis from the recovered bone marrow precursors was successful up to 5 weeks after freezing. Spleen precursors retained their osteoclastogenic capacity for 1 week after freezing, but not thereafter. The described protocol is useful for the studies of genetically modified animals as well as for screening new osteoclast-targeting therapeutics.     

High mobility group box 1 protein regulates osteoclastogenesis through direct actions on osteocytes and osteoclasts in vitro

Old age and Cx43 deletion in osteocytes are associated with increased osteocyte apoptosis and osteoclastogenesis. We previously demonstrated that apoptotic osteocytes release elevated concentrations of the proinflammatory cytokine, high mobility group box 1 protein (HMGB1) and apoptotic osteocyte conditioned media (CM) promotes osteoclast differentiation. Further, prevention of osteocyte apoptosis blocks osteoclast differentiation and attenuates the extracellular release of HMGB1 and RANKL. Moreover, sequestration of HMGB1, in turn, reduces RANKL production/release by MLO-Y4 osteocytic cells silenced for Cx43 (Cx43^def), highlighting the possibility that HMGB1 promotes apoptotic osteocyte-induced osteoclastogenesis. However, the role of HMGB1 signaling in osteocytes has not been well studied. Further, the mechanisms underlying its release and the receptor(s) responsible for its actions is not clear. We now report that a neutralizing HMGB1 antibody reduces osteoclast formation in RANKL/M-CSF treated bone marrow cells. In bone marrow macrophages (BMMs), toll-like receptor 4 (TLR4) inhibition with LPS-RS, but not receptor for advanced glycation end products (RAGE) inhibition with Azeliragon attenuated osteoclast differentiation. Further, inhibition of RAGE but not of TLR4 in osteoclast precursors reduced osteoclast number, suggesting that HGMB1 produced by osteoclasts directly affects differentiation by activating TLR4 in BMMs and RAGE in preosteoclasts. Our findings also suggest that increased osteoclastogenesis induced by apoptotic osteocytes CM is not mediated through HMGB1/RAGE activation and that direct HMGB1 actions in osteocytes stimulate pro-osteoclastogenic signal release from Cx43^def osteocytes. Based on these findings, we propose that HMGB1 exerts dual effects on osteoclasts, directly by inducing differentiation through TLR4 and RAGE activation and indirectly by increasing pro-osteoclastogenic cytokine secretion from osteocytes.     

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.