Airway structural cells regulate TLR5-mediated mucosal adjuvant activity.

Antigen-presenting cell (APC) activation is enhanced by vaccine adjuvants. Most vaccines are based on the assumption that adjuvant activity of Toll-like receptor (TLR) agonists depends on direct, functional activation of APCs. Here, we sought to establish whether TLR stimulation in non-hematopoietic cells contributes to flagellin's mucosal adjuvant activity. Nasal administration of flagellin enhanced T-cell-mediated immunity, and systemic and secretory antibody responses to coadministered antigens in a TLR5-dependent manner. Mucosal adjuvant activity was not affected by either abrogation of TLR5 signaling in hematopoietic cells or the presence of flagellin-specific, circulating neutralizing antibodies. We found that flagellin is rapidly degraded in conducting airways, does not translocate into lung parenchyma and stimulates an early immune response, suggesting that TLR5 signaling is regionalized. The flagellin-specific early response of lung was regulated by radioresistant cells expressing TLR5 (particularly the airway epithelial cells). Flagellin stimulated the epithelial production of a small set of mediators that included the chemokine CCL20, which is known to promote APC recruitment in mucosal tissues. Our data suggest that (i) the adjuvant activity of TLR agonists in mucosal vaccination may require TLR stimulation of structural cells and (ii) harnessing the effect of adjuvants on epithelial cells can improve mucosal vaccines.

NLRP3 inflammasome is required in murine asthma in the absence of aluminum adjuvant.

BACKGROUND: Inflammasome activation with the production of IL-1ß received substantial attention recently in inflammatory diseases. However, the role of inflammasome in the pathogenesis of asthma is not clear. Using an adjuvant-free model of allergic lung inflammation induced by ovalbumin (OVA), we investigated the role of NLRP3 inflammasome and related it to IL-1R1 signaling pathway. METHODS: Allergic lung inflammation induced by OVA was evaluated in vivo in mice deficient in NLRP3 inflammasome, IL-1R1, IL-1ß or IL-1α. Eosinophil recruitment, Th2 cytokine, and chemokine levels were determined in bronchoalveolar lavage fluid, lung homogenates, and mediastinal lymph node cells ex vivo. RESULTS: Allergic airway inflammation depends on NLRP3 inflammasome activation. Dendritic cell recruitment into lymph nodes, Th2 lymphocyte activation in the lung and secretion of Th2 cytokines and chemokines are reduced in the absence of NLRP3. Absence of NLRP3 and IL-1ß is associated with reduced expression of other proinflammatory cytokines such as IL-5, IL-13, IL-33, and thymic stromal lymphopoietin. Furthermore, the critical role of IL-1R1 signaling in allergic inflammation is confirmed in IL-1R1-, IL-1ß-, and IL-1α-deficient mice. CONCLUSION: NLRP3 inflammasome activation leading to IL-1 production is critical for the induction of a Th2 inflammatory allergic response.

Histamine plays an essential regulatory role in lung inflammation and protective immunity in the acute phase of Mycobacterium tuberculosis infection.

The course and outcome of infection with mycobacteria are determined by a complex interplay between the immune system of the host and the survival mechanisms developed by the bacilli. Recent data suggest a regulatory role of histamine not only in the innate but also in the adaptive immune response. We used a model of pulmonary Mycobacterium tuberculosis infection in histamine-deficient mice lacking histidine decarboxylase (HDC(-/-)), the histamine-synthesizing enzyme. To confirm that mycobacterial infection induced histamine production, we exposed mice to M. tuberculosis and compared responses in C57BL/6 (wild-type) and HDC(-/-) mice. Histamine levels increased around fivefold above baseline in infected C57BL/6 mice at day 28 of infection, whereas only small amounts were detected in the lungs of infected HDC(-/-) mice. Blocking histamine production decreased both neutrophil influx into lung tissue and the release of proinflammatory mediators, such as interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), in the acute phase of infection. However, the accumulation and activation of CD4(+) T cells were augmented in the lungs of infected HDC(-/-) mice and correlated with a distinct granuloma formation that contained abundant lymphocytic infiltration and reduced numbers of mycobacteria 28 days after infection. Furthermore, the production of IL-12, gamma interferon, and nitric oxide, as well as CD11c(+) cell influx into the lungs of infected HDC(-/-) mice, was increased. These findings indicate that histamine produced after M. tuberculosis infection may play a regulatory role not only by enhancing the pulmonary neutrophilia and production of IL-6 and TNF-alpha but also by impairing the protective Th1 response, which ultimately restricts mycobacterial growth.

Understanding the mechanism of action of bacterial superantigens from a decade of research.

In the face of the unique diversity and plasticity of the immune system pathogenic organisms have developed multiple mechanisms in adaptation to their hosts, including the expression of a particular class of molecules called superantigens. Bacterial superantigens are the most potent stimulators of T cells. The functional consequences of the expression of superantigens by bacteria can be extended not only to T lymphocytes, but also to B lymphocytes and to cells of the myeloid compartment, including antigen-presenting cells and phagocytes. The biological effects of bacterial superantigens as well as their molecular aspects have now been studied for a decade. Although there is still a long way to go to clearly understand the role these molecules play in the establishment of disease, recently acquired knowledge of their biochemistry now offers unique experimental opportunities in defining the molecular rules of T-cell activation. Here, we present some of the most recent functional and molecular aspects of the interaction of bacterial superantigens with MHC class II molecules and the T-cell receptor.

Presence or absence of TGF-beta determines IL-4-induced generation of type 1 or type 2 CD8 T cell subsets.

CD8+ T cells often differentiate into highly cytotoxic cells, secreting a Th1-like or type 1 cytokine pattern characterized by the production of IFN-gamma. However, cytotoxic, and in some reports, noncytotoxic, type 2 cells that secrete IL-4, IL-5, or IL-10 instead of IFN-gamma, can be generated when CD8+ T cells are primed in the presence of IL-4. Here, we show that IL-4 can also generate typical CD8 type 1 responses. Indeed, while presence of TGF-beta biases the development of CD8 T cells that, then, produce little cytolytic activity and IFN-gamma, addition of IL-4 results in the recovery of cytotoxicity and IFN-gamma production. The cooperative effects of TGF-beta and IL-4 imply dual functions, not only for IL-4, but also for TGF-beta. Indeed, depending on the presence or absence of IL-4, TGF-beta either inhibits or induces the generation of type 1 CD8+ T cells. Physiologically, the ratio of local IL-4/TGF-beta concentration may therefore be a critical element in determining the outcome of T cell responses to pathogen and autoantigens. It allows CD8 T cells to switch from an immunotolerant state in the presence of only TGF-beta or IL-4, to an immunocompetent proinflammatory type 1 state in the absence or presence of both cytokines.

Neoepitope immunoassay: an assay for human interleukin 1 beta based on an antibody induced conformational change.

A secondary monoclonal antibody (mAb2) was generated by immunization with immune complexes of human IL-1 beta and a primary monoclonal (mAb1). mAb2 bound to a neoepitope on the IL-1 beta/mAb1-complex with a dissociation constant (Kd) of 26 pM but not to uncomplexed IL-1 beta. As assessed by the binding of labeled IL-1 beta and neutralization of bioactivity, mAb2 enhanced the affinity of IL-1 beta to mAb1; Kd-values were 108 pM in absence and 5.4 pM in presence of mAb2. By analyzing a series of mutants of IL-1 where surface loops had been exchanged with the corresponding loops of human IL-1 receptor antagonist protein, a critical region responsible for mAb2 binding was localized to the C-terminal region. In addition to mAb1/IL-1 beta-complexes, mAb2 bound pro-IL-1 beta/mAb1 complexes as well as pro-IL-1 beta suggesting that mAb2 recognized a conformation of IL-1 beta resembling that of pro-IL-1 beta. Using this pair of mAbs, chemiluminescent and enzyme linked assays with detection limits of 2 pg/ml hIL-1 beta have been established.

IL-4 differentiates naive CD8+ T cells to a "Th2-like" phenotype: a link between viral infections and bronchial asthma.

Viral infections of the lung have been postulated to be a major factor in the etiology of bronchial asthma, a disease characterized by eosinophilic inflammation of the airways. In addition, upper respiratory tract infection in asthmatic individuals results in an exacerbation of the disease. Nevertheless, the mechanisms by which viral infection leads to disease exacerbation are poorly understood. CD8+ T cells play an important role in the host defense responses against viral infection, although to date, there are no reports to suggest that CD8+ T cells play any role in eosinophil recruitment. In the present study, we report that CD8+ T cells activated by either immobilized CD3 mAb or specific antigen can switch to a phenotype that produces Th2 cytokines and secretes less IFN-gamma. Moreover, in vivo, if a lung mucosal Th2 immune response exists, then antigen-specific activation of CD8 cells results in the development of lung eosinophilic inflammation mediated by the secretion of IL-5 from CD8+ T cells. These results may explain the link between viral infections and bronchial asthma, as this IL-4-dependent switch to CD8+ T cells to IL-5 secretion may not only exacerbate asthma by recruiting eosinophils into the lungs, but the impaired IFN-gamma production may also lead to delayed viral clearance.

Activation of the Fas receptor on lung eosinophils leads to apoptosis and the resolution of eosinophilic inflammation of the airways.

While considerable progress has been made in understanding the events by which eosinophils accumulate in various pathophysiological conditions, the mechanisms controlling the resolution of eosinophilic inflammation are poorly understood. In the present study, we demonstrate that lung eosinophils obtained by bronchoalveolar lavage (BAL) after aerosol allergen provocation of immunized mice expressed the Fas receptor. Stimulation of purified eosinophils in vitro with a monoclonal anti-Fas mAb (1 ng-1 microg/ml) induced a dose/time dependent loss of cell viability from 24-72 h. Measurement of DNA fragmentation with propidium iodide confirmed that anti-Fas induced eosinophil death by apoptosis. While incubation with IL-3, IL-5, or GM-CSF prevented spontaneous apoptosis, these factors failed to prevent anti-Fas induced apoptosis. Administration of anti-Fas mAb to the lungs after the induction of a lung eosinophilia increased the number of peroxidase positive macrophages in BAL fluid 4-12 h later which was followed by a marked reduction in the number of eosinophils in the airways. Importantly, Fas-mediated resolution of eosinophilic inflammation occurred in the absence of any overt secondary inflammatory changes in the lungs. We speculate that defects in this pathway may at least in part explain the chronic eosinophilic inflammation often observed in the lungs of asthmatic individuals.

Virus-specific CD8+ cells can switch to interleukin 5 production and induce airway eosinophilia.

Virus infections of the lung are thought to predispose individuals to asthma, a disease characterized by eosinophil infiltration of the airways. CD8+ T cells are an important part of the host response to virus infection, however, they have no reported role in eosinophil recruitment. We developed a mouse model of virus peptide-stimulated CD8+ T cell immune responses in the lung. We found that bystander CD4+ T helper cell type 2 immune responses to ovalbumin switched the virus peptide-specific CD8+ T cells in the lung to interleukin (IL) 5 production. Furthermore, when such IL-5-producing CD8 T cells were challenged via the airways with virus peptide, a significant eosinophil infiltration was induced. In vitro studies indicated that IL-4 could switch the virus-specific CD8+ T cells to IL-5 production. These results could explain the link between virus infection and acute exacerbation of asthma and, perhaps more importantly, they indicate an IL-4-dependent mechanism that would impair CD8+ T cell responses and delay viral clearance from the host.

Non-cytotoxic, IL-4, IL-5, IL-10 producing CD8+ T cells: their activation and effector functions.

CD8+ T cells activated in the presence of IL-4 can develop into distinct, non-cytotoxic CD8- and cytotoxic CD8+ subsets that produce IL-4, IL-5, IL-10 but do not produce IFN-gamma. These 'Th2 like' CD8+ cells may enhance Th2 responses, help B cells or suppress Th1 immune responses. Importantly, the switch from the cytotoxic, IFN-gamma producing CD8+ T-cell phenotype could compromise the host response to infectious agents such as HIV.

Th2-like CD8 T cells: their role in protection against infectious diseases.

The expression of cytolytic activity and production of interferon gamma (IFN-gamma) by CD8(+) T cells is thought to play a fundamental role in protection against infection by viruses and intracellular parasites. François Erard and Graham Le Gros have recently shown that CD8(+) T cells activated in the presence of interleukin 4 (IL-4) can switch development to a CD8(-)CD4(-)Th2-like phenotype that is not cytolytic and that does not produce IFN-gamma. Here they speculate on whether this IL-4-induced switch is used by the host to make a more-effective response against parasite invasion, or i f it is a host mechanism used by the parasite to evade protective CD8(+) T-cell responses.

Switch of CD8 T cells to noncytolytic CD8-CD4- cells that make TH2 cytokines and help B cells.

CD8+ T cells are a major defense against viral infections and intracellular parasites. Their production of interferon-gamma (IFN-gamma) and their cytolytic activity are key elements in the immune response to these pathogens. Mature mouse CD8+ T cells that were activated in the presence of interleukin-4 (IL-4) developed into a CD8-CD4- population that was not cytolytic and did not produce IFN-gamma. However, these CD8- cells produced large amounts of IL-4, IL-5, and IL-10 and helped activate resting B cells. Thus, CD8 effector functions are potentially diverse and could be exploited by infectious agents that switch off host protective cytolytic responses.

Human peripheral blood eosinophils produce and release interleukin-8 on stimulation with calcium ionophore.

We present evidence that human blood eosinophils produce interleukin (IL)-8 when stimulated with calcium ionophore. Following in vitro culture of 99% pure eosinophils with calcium ionophore, released IL-8 was detectable by enzyme-linked immunosorbent assay in supernatants. Eosinophil IL-8 production was considerably greater than that of IL-3 or granulocyte macrophage colony-stimulating factor. Furthermore, eosinophil production of IL-8 in the presence of calcium ionophore could be inhibited with the immunomodulating agent cyclosporin A and the protein synthesis inhibitor cycloheximide. In addition, following stimulation of highly purified blood eosinophils with calcium ionophore, IL-8 mRNA was detectable after polymerase chain reaction amplification. In comparison with other cells on stimulation with calcium ionophore, eosinophils produce about half as much IL-8 as neutrophils but significantly more than purified T cells. In contrast to monocytes and neutrophils, IL-8 production was not inducible with IL-1 or tumor necrosis factor. Finally, following calcium ionophore stimulation blood eosinophils were shown to contain cytoplasmic IL-8 by employing a monoclonal antibody against IL-8 in conjunction with immunohistochemistry. These observations demonstrate that eosinophils are capable of IL-8 production and release, which may contribute to defense against parasites and to the pathophysiology of allergic and asthmatic disease.

Interferon-alpha suppresses the capacity of T cells to help antibody production by human B cells.

This study was designed to analyze the effect of interferon-alpha (IFN-alpha) on the potential of T cells to help B-cell differentiation in vitro. Human splenic T cells preactivated via the T-cell receptor (TCR)/CD3 complex, as well as murine EL4 thymoma T cells preactivated with phorbol esters, stimulated human B cells via a species cross-reactive physical interaction to differentiate into antibody-producing cells. If the human or murine T cells were activated in the presence of IFN-alpha, normal proliferation and interleukin-2 (IL-2) production occurred, but the cells did not acquire any B-cell helper potential. Therefore, IFN-alpha modulates the B-cell stimulatory potential of T cells by interfering with the T-cell activation process. In contrast, IFN-alpha neither acted on B cells directly nor on already activated T cells, because it did not suppress B-cell differentiation induced by T cells preactivated in the absence of IFN-alpha. IFN-alpha did not induce the production of inhibitory T-cell factor(s), since T cells preactivated in the presence of IFN-alpha did not inhibit the interaction of B cells with T cells optimally preactivated in the absence of IFN-alpha. Taken together the data indicate that IFN-alpha suppresses the potential of T cells to stimulate B-cell differentiation by interfering with the T-cell activation process, but acts neither on B cells directly nor on already activated T cells.

Recombinant human C5a induces transcription but not translation of interleukin 1 beta mRNA in human monocytes.

The effect of recombinant human C5a (rhC5a) on the synthesis of interleukin 1 beta (IL-1 beta) was investigated in human monocytes, isolated by leukapheresis and countercurrent elutriation. rhC5a induced IL-1 beta mRNA synthesis in a dose- and time-dependent manner. Maximal induction was achieved at 3 h with rhC5a concentrations of 200 to 500 ng/ml. The maximal rhC5a-stimulated mRNA induction was about 75% of that observed using LPS as the stimulus (300 ng/ml). The inducing activity of rhC5a could be neutralized by preincubation with a polyclonal anti-C5a antibody. On the other hand rhC5a in optimal concentrations only weakly stimulated IL-1 beta protein synthesis, as measured by a two-site directed enzyme-linked immunoassay. When compared on Northern blots, a slightly reduced mobility of C5a-stimulated IL-1 beta mRNA was observed relative to LPS-stimulated RNA. To exclude the possibility that structural defects in the IL-1 beta mRNA are responsible for the weak translational efficiency after C5a stimulation a primer extension experiment was performed. No difference in the length of the extended fragment was detected between LPS and C5a-stimulated RNA, suggesting that the 5'-regions of the RNAs are identical. When LPS- or C5a-stimulated RNA was used to program IL-1 beta synthesis in an in vitro translation system from rabbit reticulocytes, no difference in translational efficiency was observed. Our results indicate that in human monocytes two signals for IL-1 beta gene expression are necessary, a signal for transcriptional activation and another signal to induce translation of the mRNA.

Measurement of interleukin 1 alpha and 1 beta (IL-1 alpha and IL-1 beta) in human cystic lesions of the jaw. Implications for the pathogenesis of radicular cysts.

Human radicular cystic tissue of jaws was found to contain between 0.823 pg/mg to 18.026 pg/mg interleukin 1 beta and from 0.34 pg/mg to 0.708 pg/mg interleukin 1 alpha. No IL-1 beta and alpha could be found in specimens from healthy patients. A finding which may be extremely relevant in cystic growth and episodes of alveolar bone resorption around the cystic lesion.

Transforming growth factor type beta 1 (TGF-beta 1) down-regulates interleukin-2 production and up-regulates interleukin-2 receptor expression in a thymoma cell line.

Transforming growth factor type beta 1 (TGB-beta 1) belongs to a family of polypeptides with regulatory effects on growth and differentiation of a variety of cell types. TGB-beta 1 plays an important role in regulation of immune response by acting as a negative control signal for T cell proliferation through still unknown mechanisms. In this study we have analysed the effects of TGB-beta 1 on EL 4-6.1, a variant of the murine EL 4 thymoma, which can be induced by phorbol 12-myristate 13-acetate (PMA) and/or interleukin 1 (IL-1) to secrete interleukin 2 (IL-2) and express IL-2 receptors (IL-2R). Using this defined model system, we show that TGB-beta 1 simultaneously down-regulates IL-2 expression and up-regulates the number of both high and low affinity IL-2R. These changes correlate with changes at the mRNA level, suggesting an effect at the pre-translational level. The specificity of both TGF-beta 1 effects was demonstrated using a neutralizing antiserum to TGF-beta 1. Our data also suggest that TGF-beta 1 does not interfere with early activation signals of PMA and/or IL-1. This model might be useful for elucidating the complex role of TGF-beta 1 in the regulation of T cell responses.

Increased interleukin-1 beta (IL-1 beta) concentration in gingival tissue from periodontitis patients.

Human gingival tissues from periodontitis patients were found to contain from 126 fg/mg to 2161 fg/mg interleukin-1 beta as determined by a sensitive enzyme linked immunoassay. No IL-1 beta could be found in normal gingival tissue. This finding may have important consequences relevant to connective tissue destruction and episodes of alveolar bone resorption characteristic of chronic periodontitis.