The role of B cells in in vitro induction of IFN-gamma-producing CD4+ T cells specific to Listeria monocytogens: positive and IL-10-mediated negative regulation

Systemic maternal inflammation promotes ASD via IL-6 and IFN-γ

Autism spectrum disorder (ASD) is a neurological disorder that manifests during early development, impacting individuals through their ways of communicating, social behaviors, and their ability to perform day-to-day activities. There have been different proposed mechanisms on how ASD precipitates within a patient, one of which being the impact cytokines have on fetal development once a mother's immune system has been activated (referred to as maternal immune activation, MIA). The occurrence of ASD has long been associated with elevated levels of several cytokines, including interleukin-6 (IL-6) and interferon gamma (IFN-γ). These proinflammatory cytokines can achieve high systemic levels in response to immune activating pathogens from various extrinsic sources. Transfer of cytokines such as IL-6 across the placental barrier allows accumulation in the fetus, potentially inducing neuroinflammation and consequently altering neurodevelopmental processes. Individuals who have been later diagnosed with ASD have been observed to have elevated levels of IL-6 and other proinflammatory cytokines during gestation. Moreover, the outcome of MIA has been associated with neurological effects such as impaired social interaction and an increase in repetitive behavior in animal models, supporting a mechanistic link between gestational inflammation and development of ASD-like characteristics. The present review attempts to provide a concise overview of the available preclinical and clinical data that suggest cross-talk between IL-6 and IFN-γ through both extrinsic and intrinsic factors as a central mechanism of MIA that may promote the development of ASD.

Suppression of the Bacterial Antigen-Specific T Cell Response and the Dendritic Cell Migration to the Lymph Nodes by Osteopontin

Osteopontin (OPN) has been reported to enhance the interferon (IFN)-gamma-producing Th1-type T cell response through the induction of interleukin (IL)-12 and the suppression of IL-10. We therefore investigated whether OPN could enhance Th1 induction by vaccination against bacterial antigen in vivo. Unexpectedly, the co-inoculation of OPN suppressed the induction of IFN-gamma-producing CD4(+) T cells and T cell proliferative response after the subcutaneous heat-killed Listeria monocytogenes(HKLM) immunization. These results suggest that OPN down-regulates T cell priming. Since dendritic cells (DC) play a pivotal role in T cell priming, we next analyzed the effects of OPN on DC. The addition of OPN into the culture of either bone marrow-derived immature DC or an immature DC line JAWSII showed no effects on the expression of MHC class II, CD80, and CD86 molecules before and after HKLM stimulation. Consistently, in vitro OPN-treated DC showed a normal antigen-presenting function to an established Listeria-specific Th1-type T cells. However, when the DC were transferred into the footpad with HKLM and OPN, the migration of the transferred DC into the regional LN was suppressed in comparison to the DC transferred with HKLM alone. Furthermore, the addition of OPN into the culture of the DC line and HKLM severely suppressed the HKLM-induced expression of CCR7 chemokine receptor which is an important factor in the migration of DC into LN. All the results suggest the existence of an OPN-mediated negative feedback mechanism in the T cell immune response through the regulation of DC migration.

Depressed CD40 ligand expression contributes to reduced gamma interferon production in human tuberculosis

Expression of CD40 ligand (CD40L) correlated directly with Mycobacterium tuberculosis-stimulated gamma interferon (IFN-gamma) production by peripheral blood mononuclear cells (PBMC) from tuberculosis patients and healthy tuberculin reactors. The CD40L agonist increased M. tuberculosis-induced IFN-gamma production by PBMC, and anti-CD40 or anti-CD40L antibodies reduced IFN-gamma production. CD40L expression on PBMC was reduced by exposure to B cells and to soluble factors from M. tuberculosis-infected monocytes. These findings suggest that CD40L dysregulation contributes to reduced IFN-gamma production in human tuberculosis.

Role of IL-10 in a Neonatal Mouse Listeriosis Model

This study was undertaken to test the hypothesis that altered IL-10 production plays a role in the increased susceptibility of neonates to listeriosis. Plasma IL-10 levels were measured in neonatal and adult mice at various times after infection with Listeria monocytogenes. Relative to adults, neonatal mice had markedly increased IL-10 levels early in the course of infection with Listeria using a 90% lethal dose. Higher neonatal IL-10 responses were also observed after injecting adults and pups with equal doses of killed organisms. Splenic macrophages from neonates produced higher IL-10 levels than those of adults after in vitro stimulation with killed bacteria, confirming in vivo observations. Moreover, IL-10 blockade had differential effects in neonates and adults infected with live Listeria. In adult mice, anti-IL-10 Abs decreased bacterial burden early in the course of infection, but were no longer effective at 6 days or later after challenge. In the pups, however, the same treatment had beneficial effects both early and late during infection and resulted in increased survival. Collectively, our data suggest that an overproduction of IL-10 by macrophages may at least partially explain the increased susceptibility of neonates to listeriosis, and provide further evidence that cytokine production is different in adults and neonates.

The role of B cells in the establishment of T cell response in mice infected with an intracellular bacteria, Listeria monocytogenes

To clarify the role of B cells in the establishment of T cell response against intracellular bacteria, B-cell-deficient (muMT-/-) mice were infected with an intracellular bacteria, Listeria monocytogenes, and T cell response against the bacteria was analyzed. On day 6 of primary Listeria infection, spleen T cells of the muMT-/- mice showed significantly lower levels of proliferative response and IFN-gamma production than those of normal infected mice after in vitro stimulation with listerial antigen. Even in the secondary Listeria infection after immunization with viable bacteria, spleen T cells of the muMT-/- mice proliferated and produced IFN-gamma against listerial antigen at significantly lower levels than those of normal immunized mice. These results demonstrate participation of B cells in priming of Listeria-specific T cells in vivo. However, B cells failed to present Listeria antigen to Listeria-specific T cells in vitro unless Listeria antigen was solubilized. Furthermore, transfer of immune serum from Listeria-infected normal mice failed to enhance the Listeria-specific T cell response of muMT-/- mice. The results indicate that B cells support the T cell response against intracellular bacteria through a mechanism other than their Ig production or antigen presentation function.

Listeria monocytogenes and Serratia marcescens infections as models for Th1/Th2 immunity in laboratory cats

Five species of bacteria known to be naturally-occurring pathogens of cats were screened for their ability to grow in feline macrophages in vitro, and to induce antibodies and delayed type hypersensitivity (DTH) responses in vivo. Two of these organisms, L. monocytogenes and S. marcescens, were selected for further study based on clear-cut differences in their in vitro and in vivo behavior. Listeria was macrophage tropic, induced DTH, and evoked poor antibody responses post-recovery, whereas Serratia remained extracellular, did not induce a DTH reaction, and produced high titer of antibodies. Young specific pathogen free cats were then inoculated subcutaneously into the drainage areas of the right and left popliteal and auricular lymph nodes with either L. monocytogenes or S. marcescens. Each of the four lymph nodes were then removed in sequence over a two week period, weighed, cultured for viable bacteria, and RNA extracted for Th1/Th2 cytokine mRNA quantitation. Antibody responses and delayed type hypersensitivity responses were also measured. Identical to pilot studies, cats infected with Serratia developed very high levels of antibody compared to Listeria infected cats but no DTH, while Listeria infected cats produced negligible or low titers of antibodies and strong DTH. Immunity to Listeria occurred around 168 h post infection as evidenced by the disappearance of living bacteria from the nodes, while immunity to Serratia took over 264 h. Pronounced lymph node hyperplasia occurred in both infections, but persisted longer for Serratia. Enlargement of Serratia infected nodes was associated with marked follicular, primary and secondary germinal center and medullary hyperplasia. Germinal center formation in Listeria stimulated nodes was much less intense and dense accumulations of macrophages dissected between follicles downward from the subcapsular sinuses. Although functional and histologic studies showed a clear-cut cell-mediated vs. humoral response in the respective Listeria and Serratia infections, preferential cytokine mRNA upregulation was observed for only two of the five major Th1/Th2 cytokines measured. Interferon-gamma, a Th1 cytokine, was much more elevated in the Listeria stimulated nodes, but TNF-alpha (also a Th1 cytokine) was more elevated in Serratia infected nodes. Interleukin-12, an important Th1 cytokine, was elevated to equal levels in both infections as were the Th2 cytokines IL-4 and IL-10.

Ly1- (CD5-) B cells produce interleukin (IL)-10

Interleukin (IL)-10 enhances humoral immunity by inhibiting macrophage activation and promoting the development of Th2 cytokine synthesis. In this study we investigated the ability of conventional Ly-1- (CD5-) B cells to produce IL-10 protein. Highly purified normal, naive splenic B cells from both BALB/c and C57BL/6 mice produced IL-10 in response to stimulation with the mitogen LPS. In addition, B cells from antigen primed mice also produced IL-10 upon antigen restimulation in vitro, as analyzed by ELISA and by bioassay. Removal of Ly-1+ B cells did not appreciably reduce IL-10 production, indicating that conventional Ly-1- B cells produced IL-10. These results indicate that normal Ly-1- B cells produce significant quantities of IL-10 during mitogen- or antigen-driven immune responses. The production of IL-10 by conventional B cells may enhance their capacity to promote humoral immune responses.

Osteoclast activation in inflammatory periodontal diseases

OBJECTIVE

In this paper, we review the mechanisms thought to be involved in the activation of osteoclasts in periodontitis.

SUMMARY

Osteoclasts are regulated by both microbial and host factors. Some factors act directly on cells of the osteoclast lineage, whereas others act indirectly through other cell types in the bone environment. The proinflammatory cytokines (interleukins 1 and 6, tumor necrosis factors) have been implicated in the stimulation of osteoclastic resorption. The roles of the immunoregulatory cytoknes (interleukins 2 and 4, interferon gamma) are less clear, but decreased levels of these factors may contribute to periodontitis. A number of lipid mediators may be involved in stimulation of bone resorption. These include bacterial lipopolysaccharide and host-derived platelet-activating factor and prostaglandins. More recently, reactive oxygen intermediates and extracellular nucleotides, both present at sites of inflammation, have been investigated as possible modulators of osteoclast activity. The potential use of antiresorptive therapies in periodontitis is reviewed.

CONCLUSIONS

A wide range of host and bacterial factors contribute to the loss of alveolar bone in periodontitis. However, much remains to be understood about the complex mechanisms through which these factors regulate osteoclast activity. Further studies at the cellular and molecular level will lead to a better understanding of these processes and perhaps suggest new approaches for periodontal therapy.

Endogenous interleukin-4, but not interleukin-10, is involved in suppression of host resistance against Listeria monocytogenes infection in interferon-depleted mice

The production and roles of endogenous interleukin-4 (IL-4) and IL-10 in a sublethal infection with Listeria monocytogenes were studies in normal mice and anti-gamma interferon (IFN-gamma) monoclonal antibody (MAb)-pretreated mice. In normal mice, the expression of mRNAs for IL-4 and IL-10, which was amplified by reverse transcription-PCR, was induced in the spleens and livers either early or late in infection, although the serum IL-4 and IL-10 were not detectable by enzyme-linked immunosorbent assays. In vivo administration of anti-IL-4 MAb showed no effect on antilisterial resistance, whereas anti-IL-10 MAb partially diminished the defense. In anti-IFN-gamma MAb-pretreated mice, a delay in the bacterial elimination from the spleens and livers was observed and high titers of serum IL-4 and IL-10 were induced late in infection. Production of endogenous IL-4 and IL-10 was suppressed in both CD4+ cell-and CD8+ cell depleted mice. The suppression of antilisterial resistance in anti-IFN-gamma MAb-pretreated mice was canceled when anti-IL-4 MAb was injected late in infection, whereas anti-IL-10 MAb showed no effect. These results suggest that the host immune responses were polarized into the T-helper 2 phenotype in anti-IFN-gamma MAb-pretreated mice and that inhibition of host resistance against L. monocytogenes by depletion of IFN-gamma might be attributable to IL-4 produced by T cells polarized into the T-helper 2 phenotype as well as the inhibition of the IFN-gamma effects.

Down-regulation of Listeria monocytogenes-specific Th1 cytokine response by treatment of mice with goat antibody to mouse IgD

Injection of goat anti-mouse IgD antibody (G alpha M IgD) to mice has been shown to induce polyclonal IgG1 and IgE production by B cells and IL-4 production by goat Ig-specific T cells. Surface IgD crosslinking also activates function of B cells as antigen presenting cells. Although the G alpha M IgD treatment is a well established system for regulation of immune response against antigens that bind to B cell receptor, we found that the G alpha M IgD treatment also influences immune response against irrelevant bacterial antigen. The T cells from the G alpha M IgD-treated Listeria monocytogenes-infected mice showed increased IL-4 production and decreased IFN-gamma and IL-2 production against listerial antigen compared with those from control L. monocytogenes-infected mice. Interestingly, changes were also found in antigen presenting cells in the G alpha M IgD-treated mice. MHC class II expression of both B cells and macrophages decreased significantly in the G alpha M IgD-treated mice, suggesting cytokine induced by G alpha M IgD-treatment may suppress MHC class II expression and modulate APC function in the G alpha M IgD-treated mice. In accordance with the assumption, T cells from the G alpha M IgD-treated mice produced high amount of IL-4 and IL-10 in in vitro culture with goat serum which contain goat Ig. These result suggest that G alpha M IgD treatment may modulate APC function in the G alpha M IgD-treated mice through Th2 type cytokine(s) produced by goat Ig-specific T cells, which results in changes of Th response against irrelevant antigen.

In vitro generation of IFN-gamma-producing Listeria-specific T cells is dependent on IFN-gamma production by non-NK cells

In vitro 5-day cultures of naive spleen cells with viable Listeria monocytogenes (VLM), but not heat-killed L. monocytogenes, induced CD4+ T cells that produced IFN-gamma upon secondary antigen stimulation. The VLM-induced Listeria-specific T cells produced IFN-gamma but lacked expression of IL-2 and IL-4. To study the role of IFN-gamma in the induction of the IFN-gamma-producing T cells, we added anti-IFN-gamma mAb to the primary culture and analyzed IFN-gamma production upon secondary antigen stimulation. Addition of anti-IFN-gamma mAb to the culture suppressed generation of IFN-gamma-producing CD4+ T cells, suggesting that IFN-gamma is important in the induction of IFN-gamma-producing CD4+ T cells. Furthermore, our results showed that depletion of NK cells from spleen cells by anti-asialo GM1 antibody plus complement before culture enhanced induction of IFN-gamma-producing CD4+ T cells. Although NK cells are known to produce IFN-gamma, the results indicate that NK cell-derived IFN-gamma may not be important in induction of the Listeria-specific IFN-gamma-producing CD4+ T cells in the culture system. In addition, we demonstrated that IFN-gamma expression was high in CD4+ T cells from cultures of spleen cells with VLM at the primary culture level. These results suggest that IFN-gamma derived from T cells may enhance production of IFN-gamma by CD4+ T cells, while NK cells rather suppress the induction of IFN-gamma producing CD4+ T cells.