Interferon-γ production and host protective response against Mycobacterium tuberculosis in mice lacking both IL-12p40 and IL-18

Phenotype and function of peripheral blood γδ T cells in HIV infection with tuberculosis

Background

Although γδ T cells play an essential role in immunity against Human Immunodeficiency Virus (HIV) or Mycobacterium tuberculosis (MTB), they are poorly described in HIV infection with tuberculosis (TB).

Methods

The phenotypic and functional properties of peripheral blood γδ T cells in patients with HIV/TB co-infection were analyzed compared to healthy controls and patients with HIV mono-infection or TB by direct intracellular cytokine staining (ICS).

Results

The percentage of Vδ₁ subset in HIV/TB group was significantly higher than that in TB group, while the decreased frequency of the Vδ₂ and Vγ₂Vδ₂ subsets were observed in HIV/TB group than in TB group. The percentage of CD4⁺CD8^- Vδ₂ subset in HIV/TB group was markedly lower than in TB group. However, the percentage of CD4⁺CD8⁺ Vδ₂ subset in HIV/TB group was markedly higher than HIV group or TB group. A lower percentage TNF-α and a higher percentage of IL-17A of Vδ₂ subset were observed in HIV/TB group than that in HIV mono-infection. The percentage of perforin-producing Vδ₂ subset was significantly lower in HIV/TB group than that in HIV group and TB group.

Conclusions

Our data suggested that HIV/TB co-infection altered the balance of γδ T cell subsets. The influence of HIV/TB co-infection on the function of γδ T cells to produce cytokines was complicated, which will shed light on further investigations on the mechanisms of the immune response against HIV and/or MTB infection.

Interferon-gamma promotes iron export in human macrophages to limit intracellular bacterial replication

Salmonellosis and listeriosis together accounted for more than one third of foodborne illnesses in the United States and almost half the hospitalizations for gastrointestinal diseases in 2018 while tuberculosis afflicted over 10 million people worldwide causing almost 2 million deaths. Regardless of the intrinsic virulence differences among Listeria monocytogenes, Salmonella enterica and Mycobacterium tuberculosis, these intracellular pathogens share the ability to survive and persist inside the macrophage and other cells and thrive in iron rich environments. Interferon-gamma (IFN-γ) is a central cytokine in host defense against intracellular pathogens and has been shown to promote iron export in macrophages. We hypothesize that IFN-γ decreases iron availability to intracellular pathogens consequently limiting replication in these cells. In this study, we show that IFN-γ regulates the expression of iron-related proteins hepcidin, ferroportin, and ferritin to induce iron export from macrophages. Listeria monocytogenes, S. enterica, and M. tuberculosis infections significantly induce iron sequestration in human macrophages. In contrast, IFN-γ significantly reduces hepcidin secretion in S. enterica and M. tuberculosis infected macrophages. Similarly, IFN-γ-activated macrophages express higher ferroportin levels than untreated controls even after infection with L. monocytogenes bacilli; bacterial infection greatly down-regulates ferroportin expression. Collectively, IFN-γ significantly inhibits pathogen-associated intracellular iron sequestration in macrophages and consequently retards the growth of intracellular bacterial pathogens by decreasing iron availability.

Multidimensional analyses reveal modulation of adaptive and innate immune subsets by tuberculosis vaccines

We characterize the breadth, function and phenotype of innate and adaptive cellular responses in a prevention of Mycobacterium tuberculosis infection trial. Responses are measured by whole blood intracellular cytokine staining at baseline and 70 days after vaccination with H4:IC31 (subunit vaccine containing Ag85B and TB10.4), Bacille Calmette-Guerin (BCG, a live attenuated vaccine) or placebo (n = ~30 per group). H4:IC31 vaccination induces Ag85B and TB10.4-specific CD4 T cells, and an unexpected NKTlike subset, that expresses IFN-γ, TNF and/or IL-2. BCG revaccination increases frequencies of CD4 T cell subsets that either express Th1 cytokines or IL-22, and modestly increases IFNγ-producing NK cells. In vitro BCG re-stimulation also triggers responses by donor-unrestricted T cells, which may contribute to host responses against mycobacteria. BCG, which demonstrated efficacy against sustained Mycobacterium tuberculosis infection, modulates multiple immune cell subsets, in particular conventional Th1 and Th22 cells, which should be investigated in discovery studies of correlates of protection.

Harnessing Unconventional T Cells for Immunotherapy of Tuberculosis

Even if the incidence of tuberculosis (TB) has been decreasing over the last years, the number of patients with TB is increasing worldwide. The emergence of multidrug-resistant and extensively drug-resistant TB is making control of TB more difficult. Mycobacterium bovis bacillus Calmette–Guérin vaccine fails to prevent pulmonary TB in adults, and there is an urgent need for a vaccine that is also effective in patients with human immunodeficiency virus (HIV) coinfection. Therefore, TB control may benefit on novel therapeutic options beyond antimicrobial treatment. Host-directed immunotherapies could offer therapeutic strategies for patients with drug-resistant TB or with HIV and TB coinfection. In the last years, the use of donor lymphocytes after hematopoietic stem cell transplantation has emerged as a new strategy in the cure of hematologic malignancies in order to induce graft-versus leukemia and graft-versus-infection effects. Moreover, adoptive therapy has proven to be effective in controlling cytomegalovirus and Epstein-Barr virus reactivation in immunocompromised patients with ex vivo expanded viral antigen-specific T cells. Unconventional T cells are a heterogeneous group of T lymphocytes with limited diversity. One of their characteristics is that antigen recognition is not restricted by the classical major histocompatibility complex (MHC). They include CD1 (cluster of differentiation 1)–restricted T cells, MHC-related protein-1–restricted mucosal-associated invariant T (MAIT) cells, MHC class Ib–reactive T cells, and γδ T cells. Because these T cells are genotype-independent, they are also termed “donor unrestricted” T cells. The combined features of low donor diversity and the lack of genetic restriction make these cells suitable candidates for T cell–based immunotherapy of TB.

ZBTB7B (ThPOK) Is Required for Pathogenesis of Cerebral Malaria and Protection against Pulmonary Tuberculosis

We used a genome-wide screen in N-ethyl-N-nitrosourea (ENU)-mutagenized mice to identify genes in which recessive loss-of-function mutations protect against pathological neuroinflammation. We identified an R367Q mutation in the ZBTB7B (ThPOK) protein in which homozygosity causes protection against experimental cerebral malaria (ECM) caused by infection with Plasmodium berghei ANKA. Zbtb7b^R367Q homozygous mice show a defect in the lymphoid compartment expressed as severe reduction in the number of single-positive CD4 T cells in the thymus and in the periphery, reduced brain infiltration of proinflammatory leukocytes in P. berghei ANKA-infected mice, and reduced production of proinflammatory cytokines by primary T cells ex vivo and in vivo Dampening of proinflammatory immune responses in Zbtb7b^R367Q mice is concomitant to increased susceptibility to infection with avirulent (Mycobacterium bovis BCG) and virulent (Mycobacterium tuberculosis H37Rv) mycobacteria. The R367Q mutation maps to the first DNA-binding zinc finger domain of ThPOK and causes loss of base contact by R367 in the major groove of the DNA, which is predicted to impair DNA binding. Global immunoprecipitation of ThPOK-containing chromatin complexes coupled to DNA sequencing (ChIP-seq) identified transcriptional networks and candidate genes likely to play key roles in CD4⁺ CD8⁺ T cell development and in the expression of lineage-specific functions of these cells. This study highlights ThPOK as a global regulator of immune function in which alterations may affect normal responses to infectious and inflammatory stimuli.

Mechanisms of Bacterial Superinfection Post-influenza: A Role for Unconventional T Cells

Despite the widespread application of vaccination programs and antiviral drug treatments, influenza viruses are still among the most harmful human pathogens. Indeed, influenza results in significant seasonal and pandemic morbidity and mortality. Furthermore, severe bacterial infections can occur in the aftermath of influenza virus infection, and contribute substantially to the excess morbidity and mortality associated with influenza. Here, we review the main features of influenza viruses and current knowledge about the mechanical and immune mechanisms that underlie post-influenza secondary bacterial infections. We present the emerging literature describing the role of "innate-like" unconventional T cells in post-influenza bacterial superinfection. Unconventional T cell populations span the border between the innate and adaptive arms of the immune system, and are prevalent in mucosal tissues (including the airways). They mainly comprise Natural Killer T cells, mucosal-associated invariant T cells and γδ T cells. We provide an overview of the principal functions that these cells play in pulmonary barrier functions and immunity, highlighting their unique ability to sense environmental factors and promote protection against respiratory bacterial infections. We focus on two major opportunistic pathogens involved in superinfections, namely Streptococcus pneumoniae and Staphylococcus aureus. We discuss mechanisms through which influenza viruses alter the antibacterial activity of unconventional T cells. Lastly, we discuss recent fundamental advances and possible therapeutic approaches in which unconventional T cells would be targeted to prevent post-influenza bacterial superinfections.

Natural Killer T Cells and Mucosal-Associated Invariant T Cells in Lung Infections

The immune system has been traditionally divided into two arms called innate and adaptive immunity. Typically, innate immunity refers to rapid defense mechanisms that set in motion within minutes to hours following an insult. Conversely, the adaptive immune response emerges after several days and relies on the innate immune response for its initiation and subsequent outcome. However, the recent discovery of immune cells displaying merged properties indicates that this distinction is not mutually exclusive. These populations that span the innate-adaptive border of immunity comprise, among others, CD1d-restricted natural killer T cells and MR1-restricted mucosal-associated invariant T cells. These cells have the unique ability to swiftly activate in response to non-peptidic antigens through their T cell receptor and/or to activating cytokines in order to modulate many aspects of the immune response. Despite they recirculate all through the body via the bloodstream, these cells mainly establish residency at barrier sites including lungs. Here, we discuss the current knowledge into the biology of these cells during lung (viral and bacterial) infections including activation mechanisms and functions. We also discuss future strategies targeting these cell types to optimize immune responses against respiratory pathogens.

Striking the right immunological balance prevents progression of tuberculosis

INTRODUCTION

Tuberculosis (TB) caused by infection with Mycobacterium tuberculosis (Mtb) is a major burden for human health worldwide. Current standard treatments for TB require prolonged administration of antimycobacterial drugs leading to exaggerated inflammation and tissue damage. This can result in the reactivation of latent TB culminating in TB progression. Thus, there is an unmet need to develop therapies that would shorten the duration of anti-TB treatment and to induce optimal protective immune responses to control the spread of mycobacterial infection with minimal lung pathology.

FINDINGS

Granulomata is the hallmark structure formed by the organized accumulation of immune cells including macrophages, natural killer cells, dendritic cells, neutrophils, T cells, and B cells to the site of Mtb infection. It safeguards the host by containing Mtb in latent form. However, granulomata can undergo caseation and contribute to the reactivation of latent TB, if the immune responses developed to fight mycobacterial infection are not properly controlled. Thus, an optimal balance between innate and adaptive immune cells might play a vital role in containing mycobacteria in latent form for prolonged periods and prevent the spread of Mtb infection from one individual to another.

CONCLUSION

Optimal and well-regulated immune responses against Mycobacterium tuberculosis may help to prevent the reactivation of latent TB. Moreover, therapies targeting balanced immune responses could help to improve treatment outcomes among latently infected TB patients and thereby limit the dissemination of mycobacterial infection.

Inducible nitric oxide synthase response and associated cytokine gene expression in the spleen of mice infected with Clonorchis sinensis

Clonorchis sinensis is a food-borne parasite that induces a permanent increase of nitrosation in the body upon infection. The spleen is an important secondary lymphoid organ for the regulation of immune responses locally and in the whole body. However, the functions and mechanisms of the spleen in nitric oxide (NO) responses after C. sinensis infection remain unknown. In this study, BALB/c mice were infected with 20, 40, and 80 C. sinensis metacercariae to simulate mild, moderate, and severe infections, respectively. We examined the expression of inducible nitric oxide synthase (iNOS) in the spleen and the relevant cytokine transcription in splenocytes from the mice infected with different amounts of metacercariae. The iNOS of the mice infected with 80 metacercariae was expressed in the spleen as early as 10 days post-infection (dpi) and gradually increased until 90 dpi. The iNOS expression in the mice infected with 40 metacercariae was detected only at 45 and 90 dpi, but not in the mice infected with 20 metacercariae. The level of interferon (IFN)-γ messenger RNA (mRNA) transcription in splenocytes significantly increased at 10 and 20 dpi (P < 0.05) in response to mild/moderate infection but gradually decreased to normal levels after 45 dpi. The level of IL-12p35 mRNA transcription did not change at 10 and 20 dpi but significantly decreased after 45 dpi under moderate/severe infection (P < 0.05/0.01/0.001). The level of IL-18 mRNA transcription significantly increased at 10 dpi (P < 0.05/0.01) but significantly decreased after 20 dpi (P < 0.05/0.01/0.001). These results suggest that spleen is an important organ for iNOS/NO responses, which correspond to the severity of C. sinensis infection, but cannot be attributed to the expression of the Th1 cytokines.

Principal role of IL-12p40 in the decreased Th1 and Th17 responses driven by dendritic cells of mice lacking IL-12 and IL-18

IL-12 and IL-18 are cytokines which are mainly secreted by endothelial cells and monocytes including dendritic cells. The well-known effects of IL-12 and IL-18 in the protection against bacteria and virus infection as well as tumor development are associated with their characteristics in synergistically driving the development of T helper type 1 (Th1) cells and inducing IFN-γ production. In this study, we compared the knockout effects of IL-12 and/or IL-18 genes on phenotypes and functional capabilities of dendritic cells (DCs) including their ability to polarize naive CD4(+) T cells. The expression levels of surface molecules such as MHC II, CD80, CD86 and ICOSL, and endocytic capacity were not significantly differences between DCs of wild type (WT) mice and double knockout (DKO) mice of IL-12p40 and IL-18. Additionally, DCs lacking IL-12p40 and/or IL-18 genes were equivalently efficient in inducing T cell proliferation, compared with the WT-DCs. Interestingly, IL-10 production significantly decreased in DKO-DCs, while production of other inflammation-related cytokines were unaffected in WT-DCs and DKO-DCs. Importantly, IL-12p40(-/-)-DCs and DKO-DCs severely impaired the ability to induce IFN-γ and IL-17 production from CD4(+) T cells. IL-18(-/-)-DCs also moderately decreased IL-17 production and IL-17-expressing CD4(+) T cells when co-cultured with CD4(+) T cells, demonstrating the involvement of IL-18 in driving IL-17 differentiation. Taken together, these results suggest the principal contribution of IL-12p40 in inducing Th1 and Th17 polarization, regardless of similar surface phenotypes of DCs.

A defect in the synthesis of Interferon-γ by the T cells of Complement-C5 deficient mice leads to enhanced susceptibility for tuberculosis

Interferon-γ (IFNγ) plays a major role during host defense against Mycobacterium tuberculosis (Mtb). T cells produce IFNγ in response to IL-12 and IL-18 secreted from Mtb infected macrophages. IFNγ in turn, induces nitric oxide secretion in macrophages that kills Mtb. IFNγ knockout mice are thus hyper-susceptible to tuberculosis. We reported earlier that Complement-C5 deficient (C5(-/-)) congenic mice are more susceptible to tuberculosis and showed reduced IL-12 synthesis in their macrophages. Using C5(-/-) congenic mice that carry a deletion in the C5 gene and the wild type C5(+/+) mice, we demonstrate here that, the C5(-/-) derived CD3(+) T cells, have an additional defect in the synthesis of IFNγ. C5(-/-) T cells produced lower levels of IFNγ upon stimulation by antigen presenting cells (APCs) infected with Mtb or when stimulated directly with a combination of IL-12 and IL-18. The latter was in part due to a reduced phosphorylation of STAT4 following IL-12/IL-18 stimulation. Addition of C5a peptide to IL-12/IL-18 partially restored STAT4 phosphorylation and IFNγ synthesis in C5(-/-) T cells indicating that IL-12/IL-18 mediated signaling within CD3(+) T cells involves C5a peptide. Finally, C5(-/-) T cells derived from M. bovis BCG or Mtb infected mice showed a reduced expression of T-bet (T-box expressed in T cells) transcription factor, which correlated well with a reduced T cell secretion of IFNγ. Since T-bet mediated IFNγ synthesis facilitates Th1 expansion, C5(-/-) mouse derived T cells appear to have an intrinsic defect in the production of IFNγ, which is related to C5 deficiency and this may explain their increased susceptibility to infection with Mtb and BCG.

Natural killer cells promote tissue injury and systemic inflammatory responses during fatal Ehrlichia-induced toxic shock-like syndrome

Human monocytotropic ehrlichiosis is caused by Ehrlichia chaffeensis, a Gram-negative bacterium lacking lipopolysaccharide. We have shown that fatal murine ehrlichiosis is associated with CD8(+)T cell-mediated tissue damage, tumor necrosis factor-alpha, and interleukin (IL)-10 overproduction, and CD4(+)Th1 hyporesponsiveness. In this study, we examined the relative contributions of natural killer (NK) and NKT cells in Ehrlichia-induced toxic shock. Lethal ehrlichial infection in wild-type mice induced a decline in NKT cell numbers, and late expansion and migration of activated NK cells to the liver, a main infection site that coincided with development of hepatic injury. The spatial and temporal changes in NK and NKT cells in lethally infected mice correlated with higher NK cell cytotoxic activity, higher expression of cytotoxic molecules such as granzyme B, higher production of interferon-gamma and tumor necrosis factor-alpha, increased hepatic infiltration with CD8alphaCD11c(+) dendritic cells and CD8(+)T cells, decreased splenic CD4(+)T cells, increased serum concentrations of IL-12p40, IL-18, RANTES, and monocyte chemotactic protein-1, and elevated production of IL-18 by liver mononuclear cells compared with nonlethally infected mice. Depletion of NK cells prevented development of severe liver injury, decreased serum levels of interferon-gamma, tumor necrosis factor-alpha, and IL-10, and enhanced bacterial elimination. These data indicate that NK cells promote immunopathology and defective anti-ehrlichial immunity, possibly via decreasing the protective immune response mediated by interferon-gamma producing CD4(+)Th1 and NKT cells.

Disparity in circulating peripheral blood dendritic cell subsets and cytokine profile of pulmonary tuberculosis patients compared with healthy family contacts

Dendritic cell (DC) subsets, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) play a fundamental role in immune response to Mycobacterium tuberculosis (M. tuberculosis). Flow-cytometric estimation of DC subsets showed differences in the ratio of these subsets in untreated, smear-positive pulmonary tuberculosis patients compared with healthy family contacts (HFC, p < 0.05). The percentage of pDCs (0.14 +/- 0.01) was higher than mDCs (0.12 +/- 0.01) in patients, whereas in HFC, mDCs (0.15 +/- 0.01) was higher than pDCs (0.1 +/- 0.01). The percentage of mDCs (0.15 +/- 0.01) and pDCs (0.11 +/- 0.01) was restored in treated patients. Alteration in the DC subsets before and after chemotherapy was confirmed in the follow-up of acid-fast bacilli (AFB)-positive patients. This reversal in the percentage of mDC vs pDCs implicates the influence of active disease on circulating DC subsets. The cytokine bead array revealed an inverse relationship in the circulating levels of IL-12 and IFN-gamma. High IL-12 (37.9 +/- 15.2) and low IFN-gamma (11.09 +/- 3.6) was seen in HFCs derived serum samples compared with that of patients (p < 0.05). The higher percentage of mDCs and elevated IL-12 levels was found to be associated with high risk HFCs investigated. Furthermore CpG/LPS-stimulated whole-blood culture of untreated patients expressed high IFN-alpha in pDCs and less IL-12 in mDCs compared with those of treated patients.

Disseminated and rapidly fatal tuberculosis in mice bearing a defective allele at IFN regulatory factor 8

The interferon regulatory factor (IRF) family member IRF-8 participates in IFN-gamma-dependent transcriptional activation of genes containing in their promoter regions IFN-stimulated response element or IFN-gamma activation site elements. To test the role of IRF-8 in host defenses against tuberculosis, BXH-2 mice, which bear a defective IRF-8(R294C) allele, were challenged with low doses of virulent Mycobacterium tuberculosis via the i.v. and aerosol routes. BXH-2 mice were found to be extremely susceptible to M. tuberculosis, as demonstrated by rapid and uncontrolled microbial replication in spleen, liver, and lungs leading to very early death. The BXH-2 defect was expressed very early (10 days postinfection) as uncontrolled intracellular pathogen replication in NOS2-expressing lung macrophages, impaired granuloma formation, rapid dissemination of the infection to distant sites, and rapid necrosis of infected tissues. There was complete absence of IL-12p40 induction, severely reduced IFN-gamma production, and impaired T cell priming in the lungs of infected BXH-2, highlighting the critical role of IRF-8 in this process. Collectively, these results identify IRF-8 as a critical regulator of host defenses against tuberculosis.

Whatever turns you on: accessory-cell-dependent activation of NK cells by pathogens

Natural killer (NK) cells have a crucial role in combating infections and cancers and their surface receptors can directly recognize and respond to damaged, transformed or non-self cells. Whereas some virus-infected cells are recognized by this same route, NK-cell responses to many pathogens are triggered by a different mechanism. Activation of NK cells by these pathogens requires the presence of accessory cells such as monocytes, macrophages and dendritic cells. Recent studies have identified numerous pathogen-recognition receptors that enable accessory cells to recognize different pathogens and subsequently transmit signals--both soluble and contact-dependent--to NK cells, which respond by upregulating their cytotoxic potential and the production of inflammatory cytokines.

Activation of dendritic cells and induction of CD4(+) T cell differentiation by aluminum-containing adjuvants

Aluminum-containing adjuvants are widely used in licensed human and veterinary vaccines. However, the mechanism by which these adjuvants enhance the immune response and predominantly stimulate a T(H)2 humoral immune response is not well understood. In this study, the effects of aluminum hydroxide and aluminum phosphate adjuvants on antigen presentation, expression of costimulatory molecules and cytokines by mouse dendritic cells (DCs) and the ability of DCs to induce T helper cell differentiation were investigated. Dendritic cells pulsed with ovalbumin (OVA) adsorbed to aluminum-containing adjuvants activated antigen-specific T cells more effectively than DCs pulsed with OVA alone. Aluminum hydroxide adjuvant had a significantly stronger effect than aluminum phosphate adjuvant. Both aluminum-containing adjuvants significantly increased the expression of CD86 on DCs but only aluminum hydroxide adjuvant also induced moderate expression of CD80. Aluminum-containing adjuvants stimulated the release of IL-1beta and IL-18 from DCs via caspase-1 activation. DCs incubated with LPS and OVA induced T(H)1 differentiation of naïve CD4(+) T cells. In contrast, DCs incubated with aluminum/OVA activated CD4(+) T cells to secrete IL-4 and IL-5 as well as IFN-gamma. Addition of neutralizing anti-IL-1beta antibodies decreased IL-5 production and addition of anti-IL-18 antibodies decreased both IL-4 and IL-5 production. Inhibition of IL-1beta and IL-18 secretion by DCs via inhibition of caspase-1 also led to a marked decrease of IL-4 and IL-5 by CD4(+) T cells. These results indicate that aluminum-containing adjuvants activate DCs and influence their ability to direct T(H)1 and T(H)2 responses through the secretion of IL-1beta and IL-18.

What is the role of Toll-like receptors in bacterial infections?

Innate immunity relies on signalling by Toll-like receptors (TLRs) to alert the immune system of the presence of invading bacteria. TLR activation leads to the release of cytokines that allow for effective innate and adaptive immune responses. However, the contribution of different TLRs depends on the site of the infection and the pathogen. This review will describe the involvement of TLRs in the development of three different bacterial infections as well as our current understanding of the role of TLRs during microbial pathogenesis.

Regulation by Jun N-terminal kinase/stress activated protein kinase of cytokine expression in Mycobacterium avium subsp paratuberculosis-infected bovine monocytes

OBJECTIVE

To evaluate activation of Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) pathway in bovine monocytes after incubation with Mycobacterium avium subsp paratuberculosis (Mptb) organisms.

SAMPLE POPULATION

Bovine monocytes obtained from 4 healthy adult Holstein dairy cows.

PROCEDURES

Bovine monocytes were incubated with Mptb organisms with or without a specific inhibitor of the JNK/SAPK pathway (SP600125) for 2, 6, 24, or 72 hours. Expression of interleukin (IL)-1beta, IL-10, IL-12, IL-18; transforming growth factor-beta (TGF-beta); and tumor necrosis factor-alpha (TNF-alpha) and the capacity of Mptb-infected monocytes to acidify phagosomes and kill Mptb organisms were evaluated. Phosphorylation status of JNK/SAPK was evaluated at 10, 30, and 60 minutes after Mptb incubation.

RESULTS

Compared with uninfected control monocytes, Mptb-infected monocytes had increased expression of IL-10 at 2 and 6 hours after incubation and had increased expression of TNF-alpha, IL-1beta, IL-18, and TGF-beta at 2, 4, and 6 hours. Additionally, Mptb-infected monocytes had increased expression of IL-12 at 6 and 24 hours. Addition of SP600125 (specific chemical inhibitor of JNK/SAPK) resulted in a decrease in TNF-alpha expression at 2, 6, and 24 hours, compared with untreated Mptb-infected cells. Addition of SP600125 resulted in a decrease in TGF-beta expression at 24 hours and an increase in IL-18 expression at 6 hours. Addition of SP600125 failed to alter phagosome acidification but did enhance the capacity of monocytes to kill Mptb organisms.

CONCLUSIONS AND CLINICAL RELEVANCE

Activation of JNK/SAPK may be an important mechanism used by Mptb to regulate cytokine expression in bovine monocytes for survival and to alter inflammatory and immune responses.

Responses to Leishmania donovani in mice deficient in interleukin-12 (IL-12), IL-12/IL-23, or IL-18

Interleukin-12 (IL-12) orchestrates acquired resistance in intracellular Leishmania donovani infection in the liver, inducing gamma interferon and, in turn, macrophage activation and parasite killing. Nevertheless, testing in IL-18(-/-) mice compared to wild-type mice and in IL-12p40(-/-) compared to IL-12p35(-/-) mice also suggested both early-acting (IL-18) and late-acting (IL-23) antileishmanial effects independent of IL-12.

Mitogen activated protein kinasep38 pathway is an important component of the anti-inflammatory response in Mycobacterium avium subsp. paratuberculosis-infected bovine monocytes

We investigated the role of cell signaling through the mitogen-activated protein kinase-p38 (MAPK p38) pathway on the antimicrobial functions and cytokine expression by bovine monocytes after ingestion of Mycobacterium avium subsp. paratuberculosis. We evaluated the dynamic secretion of interleukin (IL)-10, IL-12 and tumor necrosis factor-alpha (TNF-alpha) as well as phagosome acidification and organism killing at several time points after in vitro infection of bovine monocytes with M. avium subsp. paratuberculosis. Monocytes treated with M. avium subsp. paratuberculosis had a significant increase in IL-10 expression at 2, 4, and 6h post-infection and an increase expression of TNF-alpha at 2, 4, 6, and 24h post-infection. In contrast, IL-12 expression did not increase at any time point post-infection. Moreover, MAPK p38 was rapidly phosphorylated at 10 and 60 min after M. avium subsp. paratuberculosis ingestion. Chemical inhibition of the MAPK p38 signaling pathway (SB203580) resulted in decreased expression of IL-10 and increased expression of IL-12 at 6h post-infection. Chemically blocking the MAPK p38 pathway also increased acidification of phagosomes as well as increasing the capacity of macrophages to kill organisms. Taken together, these results indicated that selective activation of MAPK p38 may be a major mechanism exploited by M. avium subsp. paratuberculosis to circumvent the antimycobacterial effects of mononuclear phagocytes.

Neutralization of tumor necrosis factor alpha suppresses antigen-specific type 1 cytokine responses and reverses the inhibition of mycobacterial survival in cocultures of immune guinea pig T lymphocytes and infected macrophages

Neutralization of tumor necrosis factor alpha (TNF-alpha) significantly down-regulated antigen-induced lymphoproliferation and the expression of interleukin-12 p40 and gamma interferon mRNA and enhanced the viability of intracellular attenuated and virulent mycobacteria in cocultures of immune T cells and macrophages obtained from Mycobacterium bovis BCG-vaccinated guinea pigs. This suggests the crucial role of TNF-alpha in the activation of a type 1 T-cell response against Mycobacterium tuberculosis infection.

Pulmonary interleukin-23 gene delivery increases local T-cell immunity and controls growth of Mycobacterium tuberculosis in the lungs

Interleukin-23 (IL-23) is a heterodimeric cytokine that shares IL-12 p40 but contains a unique p19 subunit similar to IL-12 p35. Previous studies indicate a greater importance for intact IL-12/23 p40 expression than IL-12 p35 for immunity against Mycobacterium tuberculosis, suggesting a role for IL-23 in host defense. The effects of IL-23 on the outcome of pulmonary infection with M. tuberculosis have not been described. Here, we show that local delivery of replication-defective adenovirus vectors encoding IL-23 (AdIL-23) greatly stimulated expression of both gamma interferon (IFN-gamma) and IL-17 in lung tissues of otherwise normal mice. When given 72 h prior to infection with M. tuberculosis, AdIL-23 significantly reduced the bacterial burden at 14, 21, and 28 days. Markedly lower levels of lung inflammation were observed at 28 days than in control mice pretreated with control adenovirus (AdNull) or vehicle controls. AdIL-23 pretreatment resulted in increased numbers of CD4(+) CD25(+) activated T cells in lungs and draining lymph nodes compared to control groups and more CD4(+) T cells bearing surface memory markers in lung lymph nodes. IL-23 gene delivery also significantly enhanced host anti-mycobacterial T-cell responses, as shown by elevated levels of IFN-gamma and IL-17 secreted in vitro following restimulation with M. tuberculosis purified protein derivative. Overall, our data show that transient IL-23 gene delivery in the lung is well tolerated, and they provide the initial demonstration that this factor controls mycobacterial growth while augmenting early pulmonary T-cell immunity.

Prevention of Relapse after Chemotherapy in a Chronic Intracellular Infection: Mechanisms in Experimental Visceral Leishmaniasis

In visceral leishmaniasis, chemotherapy probably seldom eradicates all parasites in tissue macrophages; nevertheless, most T cell-intact patients show long-lasting clinical cure after treatment despite residual intracellular infection. To characterize prevention of posttreatment relapse, amphotericin B was used to kill approximately 90-95% of Leishmania donovani in livers of mice deficient in mechanisms of acquired antileishmanial resistance. Recrudescence subsequently developed 1) in animals deficient in both CD4 and CD8 T cells as well as CD40L-mediated T cell costimulation, but not in a) CD4 or CD8 cells alone, b) NK cell lytic activity, or c) ICAM-1-recruited monocytes; and 2) in mice deficient in IFN-gamma, but not in the IFN-gamma-inducing cytokines, a) IL-12, b) IL-12 and IL-23, or c) IL-18. Posttreatment recrudescence also did not develop in animals deficient in macrophage phagocyte NADPH oxidase (phox) or inducible NO synthase (iNOS) alone or, surprisingly, in those deficient in both phox and iNOS. Therefore, regulation of the intracellular replication of residual Leishmania donovani that escape chemotherapy evolves to a host mechanism distinguishable from initial acquired resistance at the T cell, cytokine, and macrophage levels. Posttreatment, either CD8 or CD4 cells can direct the response, IL-12 is not required, and iNOS and phox, the activated macrophage's primary IFN-gamma-inducible leishmanicidal pathways, both become dispensable.