Difference in neutrophil cytokine production induced by pathogenic and non-pathogenic mycobacteria

Evaluation of the innate immune response of caprine neutrophils against Mycobacterium avium subspecies paratuberculosis in vitro

Neutrophils constitute an essential component of the innate immune response, readily killing most bacteria through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs) among other mechanisms. These cells play an unclear role in mycobacterial infections such as Mycobacterium avium subspecies paratuberculosis (Map), the etiological agent of paratuberculosis, and its response is particularly understudied in ruminants. Herein, a wide set of techniques were adapted, or newly developed, to study the in vitro response of caprine neutrophils after Map infection. Immunofluorescence was used to demonstrate, simultaneously, chemotaxis, phagocytosis, degranulation, and NETs. The quantification of neutrophil phagocytic activity against Map at a 1:10 multiplicity of infection (MOI), through flow cytometry, showed values that varied from 4.54 to 5.63% of phagocyting neutrophils. By immunofluorescence, a 73.3 ± 14.5% of the fields showed NETs, and the mean release of DNA, attributable to NETosis, calculated through a fluorometric method, was 16.2 ± 3.5%. In addition, the RNA expression of TGF-β, TNF and IL-1β cytokines, measured through reverse transcription qPCR, was significantly higher in the two latter. Overall, neutrophil response was proportional to the number of bacteria. This work confirms that the simultaneous study of several neutrophil mechanisms, and the combination of different methodologies, are essential to reach a comprehensive understanding of neutrophil response against pathogens, demonstrates that, in vitro, caprine neutrophils display a strong innate response against Map, using their entire repertoire of effector functions, and sets the basis for further in vitro and in vivo studies on the role of neutrophils in paratuberculosis.

The roles of neutrophils in non-tuberculous mycobacterial pulmonary disease

Non-tuberculous Mycobacterial Pulmonary Disease (NTM-PD) is an increasingly recognised global health issue. Studies have suggested that neutrophils may play an important role in controlling NTM infection and contribute to protective immune responses within the early phase of infection. However, these cells are also adversely associated with disease progression and exacerbation and can contribute to pathology, for example in the development of bronchiectasis. In this review, we discuss the key findings and latest evidence regarding the diverse functions of neutrophils in NTM infection. First, we focus on studies that implicate neutrophils in the early response to NTM infection and the evidence reporting neutrophils' capability to kill NTM. Next, we present an overview of the positive and negative effects that characterise the bidirectional relationship between neutrophils and adaptive immunity. We consider the pathological role of neutrophils in driving the clinical phenotype of NTM-PD including bronchiectasis. Finally, we highlight the current promising treatments in development targeting neutrophils in airways diseases. Clearly, more insights on the roles of neutrophils in NTM-PD are needed in order to inform both preventative strategies and host-directed therapy for these important infections.

Live Vaccines Have Different NK Cells and Neutrophils Requirements for the Development of a Protective Immune Response Against Tuberculosis

It has been shown that neutrophils drive NK cells to activate DCs while NK cells regulate neutrophils survival. In response to mycobacteria, NK cells proliferate and produces IFN-γ, that appears to regulate the neutrophilic inflammatory responses to both M. tuberculosis infection and BCG vaccination. Although the role of neutrophils in the immune response to tuberculosis is a matter of debate, neutrophils were shown to be crucial to induce specific response against mc²-CMX vaccine. The objective of this study was to investigate the interplay between NK cells and neutrophils in regard to the development of a protective immune response against M. tuberculosis. Depletion of NK cells during vaccination did not alter the total number of neutrophils or DCs, but reduced the number of activated DCs, thus reducing the generation of Th1 specific immune responses and the protection conferred by mc²-CMX and BCG vaccines. However, only in mc²-CMX vaccination that neutrophil depletion interfered with the NK cell numbers and protection. In conclusion, it was shown that only when both NK and neutrophils were present, specific Th1 response and protection was achieved by mc²-CMX vaccine, while neutrophils although activated upon BCG vaccination were not necessary for the induced protection.

A joint effort: The interplay between the innate and the adaptive immune system in Lyme arthritis

Articular joints are a major target of Borrelia burgdorferi, the causative agent of Lyme arthritis. Despite antibiotic treatment, recurrent or persistent Lyme arthritis is observed in a significant number of patients. The host immune response plays a crucial role in this chronic arthritic joint complication of Borrelia infections. During the early stages of B. burgdorferi infection, a major hinder in generating a proper host immune response is the lack of induction of a strong adaptive immune response. This may lead to a delayed hyperinflammatory reaction later in the disease. Several mechanisms have been suggested that might be pivotal for the development of Lyme arthritis and will be highlighted in this review, from molecular mimicry of matrix metallopeptidases and glycosaminoglycans, to autoimmune responses to live bacteria, or remnants of Borrelia spirochetes in joints. Murine studies have suggested that the inflammatory responses are initiated by innate immune cells, but this does not exclude the involvement of the adaptive immune system in this dysregulated immune profile. Genetic predisposition, via human leukocyte antigen-DR isotype and microRNA expression, has been associated with the development of antibiotic-refractory Lyme arthritis. Yet the ultimate cause for (antibiotic-refractory) Lyme arthritis remains unknown. Complex processes of different immune cells and signaling cascades are involved in the development of Lyme arthritis. When these various mechanisms are fully been unraveled, new treatment strategies can be developed to target (antibiotic-refractory) Lyme arthritis more effectively.

Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis

Mycobacterium smegmatis rarely causes disease in the immunocompetent, but reported cases of soft tissue infection describe abscess formation requiring surgical debridement for resolution. Neutrophils are the first innate immune cells to accumulate at sites of bacterial infection, where reactive oxygen species and proteolytic enzymes are used to kill microbial invaders. As these phagocytic cells play central roles in protection from most bacteria, we assessed human neutrophil phagocytosis and granule exocytosis in response to serum opsonized or non-opsonized M. smegmatis mc². Although phagocytosis was enhanced by serum opsonization, M. smegmatis did not induce exocytosis of secretory vesicles or azurophilic granules at any time point tested, with or without serum opsonization. At early time points, opsonized M. smegmatis induced significant gelatinase granule exocytosis compared to non-opsonized bacteria. Differences in granule release between opsonized and non-opsonized M. smegmatis decreased in magnitude over the time course examined, with bacteria also evoking specific granule exocytosis by six hours after addition to cultured primary single-donor human neutrophils. Supernatants from neutrophils challenged with opsonized M. smegmatis were able to digest gelatin, suggesting that complement and gelatinase granule exocytosis can contribute to neutrophil-mediated tissue damage seen in these rare soft tissue infections.

The ATC/TTC haplotype in the Interleukin 8 gene in response to Gram-negative bacteria: A pilot study

OBJECTIVE

The aim of this study was to investigate the functionality of ATC/TTC (Hap-1) and ATT/TTC (Hap-2) Interleukin (IL) 8 gene haplotypes in the response of neutrophils to Gram-negative bacteria associated with periodontitis.

DESIGN

Neutrophils were isolated by gradient centrifugation from whole peripheral blood of systemically healthy individuals presenting the two IL8 gene haplotypes. Neutrophils were stimulated with P. gingivalis, A. actinomycetemcomitans and PMA/ionomycin. Cytokine gene expression (RT-qPCR) and migration/chemotaxis (boyden chamber assay) were compared according to the presence of Hap-1 or Hap-2 haplotypes. Protein production was also evaluted in the multiplex assay using the mixed population of leukocytes present in the whole blood from the same individuals. The influence of these two haplotypes on the IL8 promoter activity was assessed in gene-reporter experiments.

RESULTS

Hap-1 haplotype in neutrophils and leukocytes exacerbated the response to stimulation with Gram-negative bacteria, with higher levels of TNF-α (mRNA and protein), IL-1β, IL-2R and IFN-γ (protein) and with increased chemotaxis. Presence of the T allele at the rs4071 polymorphism (alias -251) was associated with increased activity of IL8 proximal promoter.

CONCLUSIONS

Neutrophils and leukocytes carrying the Hap-1 haplotype (ATC/TTC) in the IL8 gene present an enhanced response to stimulation with Gram-negative bacteria associated with periodontitis. Presence of the T allele (rs4073) in the IL8 proximal promoter increases transcription activity.

Re-Examining Neutrophil Participation in GN

Significant advances in understanding the pathogenesis of GN have occurred in recent decades. Among those advances is the finding that both innate and adaptive immune cells contribute to the development of GN. Neutrophils were recognized as key contributors in early animal models of GN, at a time when the prevailing view considered neutrophils to function as nonspecific effector cells that die quickly after performing antimicrobial functions. However, advances over the past two decades have shown that neutrophil functions are more complex and sophisticated. Specifically, research has revealed that neutrophil survival is regulated by the inflammatory milieu and that neutrophils demonstrate plasticity, mediate microbial killing through previously unrecognized mechanisms, demonstrate transcriptional activity leading to the release of cytokines and chemokines, interact with and regulate cells of the innate and adaptive immune systems, and contribute to the resolution of inflammation. Therefore, neutrophil participation in glomerular diseases deserves re-evaluation. In this review, we describe advances in understanding classic neutrophil functions, review the expanded roles of neutrophils in innate and adaptive immune responses, and summarize current knowledge of neutrophil contributions to GN.

Correlation between lymph node pathology and chemokine expression during bovine tuberculosis

Bovine tuberculosis is a disease of worldwide importance yet comparatively little is known about chemokine responses to infection. We report on the levels of chemokine expression within lymph nodes of cattle infected with Mycobacterium bovis when infection would be well established. Expression levels of a number of chemokines were increased in infected cattle and could be correlated to levels of respective chemokine receptors. Several chemokines were significantly correlated to pathology within the lymph node, indicating a direct relationship between chemokine expression and disease. Vaccinated animals challenged with M. bovis had lower levels of chemokine expression than unvaccinated, challenged animals, correlating with lower levels of disease in vaccinated animals. The chemokine expression profile correlated with previous evidence for a pro-inflammatory bias within the lymph node. At this stage of infection we suggest there is on-going chemokine expression by cells associated with the granuloma and continual recruitment of cells to control infection.

Neutrophils in tuberculosis: friend or foe?

Neutrophils are rapidly recruited to sites of mycobacterial infection, where they phagocytose bacilli. Whether neutrophils can kill mycobacteria in vivo probably depends on the tissue microenvironment, stage of infection, individual host, and infecting organism. The interaction of neutrophils with macrophages, as well as the downstream effects on T cell activity, could result in a range of outcomes from early clearance of infection to dissemination of viable bacteria together with an attenuated acquired immune response. In established disease, neutrophils accumulate in situations of high pathogen load or immunological dysfunction, and are likely to contribute to pathology. These activities may have clinical importance in terms of new treatments, targeted interventions and vaccine strategies.

The non-pathogenic mycobacteria M. smegmatis and M. fortuitum induce rapid host cell apoptosis via a caspase-3 and TNF dependent pathway

Background

The HIV pandemic raised the potential for facultative-pathogenic mycobacterial species like, Mycobacterium kansasii, to cause disseminating disease in humans with immune deficiencies. In contrast, non-pathogenic mycobacterial species, like M. smegmatis, are not known to cause disseminating disease even in immunocompromised individuals. We hypothesized that this difference in phenotype could be explained by the strong induction of an innate immune response by the non-pathogenic mycobacterial species.

Results

A comparison of two rapid-growing, non-pathogenic species (M. smegmatis and M. fortuitum) with two facultative-pathogenic species (M. kansasii and M. bovis BCG) demonstrated that only the non-pathogenic bacteria induced strong apoptosis in human THP-1 cells and murine bone marrow-derived macrophages (BMDM) and dendritic cells (BMDD). The phospho-myo-inositol modification of lipoarabinomannan (PI-LAM) isolated from non-pathogenic species may be one of the cell wall components responsible for the pro-inflammatory activity of the whole bacteria. Indeed, PI-LAM induces high levels of apoptosis and IL-12 expression compared to the mannosyl modification of LAM isolated from facultative-pathogenic mycobacteria. The apoptosis induced by non-pathogenic M. smegmatis was dependent upon caspase-3 activation and TNF secretion. Consistently, BALB/c BMDM responded by secreting large amounts of TNF upon infection with non-pathogenic but not facultative-pathogenic mycobacteria. Interestingly, C57Bl/6 BMDM do not undergo apoptosis upon infection with non-pathogenic mycobacteria despite the fact that they still induce an increase in TNF secretion. This suggests that the host cell signaling pathways are different between these two mouse genotypes and that TNF is necessary but not sufficient to induce host cell apoptosis.

Conclusion

These results demonstrate a much stronger induction of the innate immune response by non-pathogenic versus facultative-pathogenic mycobacteria as measured by host cell apoptosis, IL-12 and TNF cytokine induction. These observations lend support to the hypothesis that the strong induction of the innate immune response is a major reason for the lack of pathogenicity in fast-growing mycobacteria.

Polymorphonuclear neutrophils and T lymphocytes: strange bedfellows or brothers in arms?

Polymorphonuclear neutrophils (PMN) are linked invariably to the innate immune response, particularly to the defence against bacterial infection. T lymphocytes are studied mainly in virus infections, the defence against tumours, the development and progression of chronic inflammatory processes, in autoimmune phenomena and in materno-fetal tolerance. There is, however, increasing evidence for communication and interactions between PMN and T cells that we discuss here in the context of different physiological and pathological conditions, including acute and chronic inflammatory disease, defence against tumours, and maintenance of pregnancy.

Bbeta15-42 (FX06) reduces pulmonary, myocardial, liver, and small intestine damage in a pig model of hemorrhagic shock and reperfusion

OBJECTIVE

The fibrin-derived peptide Bbeta15-42 (also called FX06) has been shown to reduce myocardial infarct size following ischemia/reperfusion. Hemorrhagic shock (HS) followed by volume resuscitation represents a similar scenario, whereby a whole organism is vulnerable to reperfusion injury.

DESIGN

We subjected male farm-bred landrace pigs ( approximately 30 kg) to HS by withdrawing blood to a mean arterial pressure of 40 mm Hg for 60 minutes. Pigs were then resuscitated with shed blood and crystalloids for 60 minutes, and at this time, FX06 (2.4 mg/kg, n = 8) or vehicle control (phosphate buffered saline; 2.4 mg/kg, n = 7) was injected as an intravenous bolus.

SETTING

University hospital laboratory.

SUBJECTS

Anesthetized male farm-bred landrace pigs.

MEASUREMENTS AND MAIN RESULTS

Data are presented as mean +/- sd. Five hours after resuscitation, controls presented acute lung injury (Pao2/Fio2-ratio <300 mm Hg; extra-vascular lung water index (marker for lung injury): 9.0 +/- 1.8 mL/kg) and myocardial dysfunction/damage (cardiac index: 4.3 +/- 0.25 L/min/m; stroke volume index: 30 +/- 6 mL/m; cardiac TnT levels: 0.58 +/- 0.25 ng/mL). In contrast, FX06-treated animals showed significantly improved pulmonary and circulatory function (Pao2/Fio2-ratio >*400 mm Hg; extra-vascular lung water index: *5.2 +/- 2.1 mL/kg, cardiac index: *6.3 +/- 1.4 L/min/m; stroke volume index: *51 +/- 11 mL/m; cardiac TnT levels: *0.11 +/- 0.09 ng/mL; *p < 0.05). Also, tissue oxygenation (tpO2; mm Hg) was significantly improved during reperfusion in FX06-treated pigs when compared with controls (liver 51 +/- 4 vs. *65 +/- 4; serosa 44 +/- 5 vs. *55 +/- 7; mucosa 14 +/- 4 vs. *26 +/- 4). Finally, FX06 reduced accumulation of myeloperoxidase-positive cells (mainly neutrophils) in myocardium, liver, and small intestine and reduced interleukin-6 plasma levels (*p < 0.05; compared with controls).

CONCLUSION

We conclude that in a pig model of HS and reperfusion, administration of FX06 during reperfusion protects shock- susceptible organs such as heart, lung, liver, and small intestine.

The alternative sigma factor SigF of Mycobacterium smegmatis is required for survival of heat shock, acidic pH and oxidative stress

The alternative sigma factor SigF of Mycobacterium tuberculosis has been characterized in detail as a general-stress, stationary-phase sigma factor involved in the virulence of the bacterium. While a homologous gene has been annotated in the genome of the fast-growing Mycobacterium smegmatis, little experimental evidence is available on the function of this gene. Here, we demonstrate that SigF of M. smegmatis is required for resistance to hydrogen peroxide, heat shock and acidic pH, but not for survival in human neutrophils. No difference in sensitivity to isoniazid was observed between the wild-type strain and the DeltasigF mutant, suggesting that SigF-mediated resistance to hydrogen peroxide was via a pathway independent of KatG or AhpC. RT-PCR and 5'-RACE (rapid amplification of cDNA ends) analyses showed that sigF of M. smegmatis was co-transcribed with rsbW (thought to encode an anti-sigma factor for SigF) and MSMEG_1802 (unknown function) and was expressed from two promoters, one upstream of MSMEG_1802 and the second upstream of rsbW. Analysis of transcriptional lacZ fusion constructs in the sigF-deletion background revealed that the MSMEG_1802 promoter was dependent on SigF for expression. Moreover, MSMEG_1802-lacZ was induced twofold upon entry into stationary phase, while exposure of exponentially growing cultures to various stress conditions (e.g. heat, cold, ethanol, hydrogen peroxide or different pH values) did not lead to induction of MSMEG_1802-lacZ. Expression of rsbW-lacZ was independent of SigF and remained constant throughout the growth cycle and under various stress conditions unless the bacteria were challenged with d-cycloserine.

Non-pathogenic Mycobacterium smegmatis induces the differentiation of human monocytes directly into fully mature dendritic cells

Mycobacterium smegmatis infects human monocytes that can be precursors of dendritic cells. We tested whether the interaction of M. smegmatis with monocytes modulated their differentiation into dendritic cells. We found that M. smegmatis-infected monocytes differentiated into CD1a-CCR7+ dendritic cells in the presence of GM-CSF and IL-4 and acquired a mature phenotype since they expressed CD83 molecules in the absence of maturation stimuli. Dendritic cells derived from M. smegmatis-infected monocytes stimulated with bacterial products, produced IL-10 and still retained the capacity to produce IL-12. Consequently, they polarized naïve T lymphocytes towards a mixed Th1/Th2 immune response inducing both IFN-gamma and IL-4 production. These findings suggest that the exposure to environmental mycobacteria could modulate the differentiation of dendritic cells making them able to migrate into secondary lymphoid organs and modulate the adaptive immune response. This could explain one of the mechanisms by which environmental mycobacteria can influence the immune response to pathogenic species.

Guinea pig neutrophils infected with Mycobacterium tuberculosis produce cytokines which activate alveolar macrophages in noncontact cultures

The early influx of neutrophils to the site of infection may be an important step in host resistance against Mycobacterium tuberculosis. In this study, we investigated the effect of M. tuberculosis infection on the ability of guinea pig neutrophils to produce interleukin-8 (IL-8; CXCL8) and tumor necrosis factor alpha (TNF-alpha) and to activate alveolar macrophages. Neutrophils and alveolar macrophages were isolated from naïve guinea pigs, cultured together or alone, and infected with virulent M. tuberculosis for 3, 12, and 24 h. IL-8 protein production in cocultures, as measured by using an enzyme-linked immunosorbent assay, was found to be additive at 24 h and significantly greater in M. tuberculosis-infected cocultures than in uninfected cocultures and in cultures of the infected neutrophils or macrophages alone. The IL-8 mRNA levels, determined by real-time reverse transcription-PCR, were elevated at 24 h in infected cocultures and infected cells cultured alone. In order to elucidate the contributions of neutrophils and their soluble mediators to the activation of alveolar macrophages, neutrophils and alveolar macrophages were cultured in a contact-independent manner by using a Transwell insert system. Neutrophils were infected with virulent M. tuberculosis in the upper wells, and alveolar macrophages were cultured in the lower wells. The release of hydrogen peroxide from alveolar macrophages exposed to soluble products from infected neutrophils was significantly increased compared to that from unexposed alveolar macrophages. Significant up-regulation of IL-1beta and TNF-alpha mRNA levels in alveolar macrophages was observed at 24 and 30 h, respectively, compared to those in cells not exposed to soluble neutrophil products. Treatment with anti-guinea pig TNF-alpha polyclonal antibody completely abolished the response of alveolar macrophages to neutrophil products. This finding suggests that TNF-alpha produced by infected neutrophils may be involved in the activation of alveolar macrophages and hence may contribute to the containment of M. tuberculosis infection during the early period of infection.

M. leprae inhibits apoptosis in THP-1 cells by downregulation of Bad and Bak and upregulation of Mcl-1 gene expression

Background

Virulent Mycobacterium leprae interfere with host defense mechanisms such as cytokine activation and apoptosis. The mitochondrial pathway of apoptosis is regulated by the Bcl-2 family of proteins. Expression of Fas ligand and apoptotic proteins is found in leprosy lesions and M. leprae has been shown to activate pro-apoptotic Bcl-2 genes, Bak and Bax. However, the mechanism by which M. leprae modulates apoptosis is as yet unclear. We investigated expression of apoptotic genes in THP-1 monocytes in response to infection by M. leprae and non-pathogenic M. bovis BCG.

Results

M. leprae did not induce apoptosis in THP-1 cells, while BCG induced a significant loss of cell viability by 18 h post-infection at both (multiplicity of infection) MOI-10 and 20, with an increase by 48 h. BCG-induced cell death was accompanied by characteristic apoptotic DNA laddering in cells. Non-viable BCG had a limited effect on host cell death suggesting that BCG-induced apoptosis was a function of mycobacterial viability. M. leprae also activated lower levels of TNF-alpha secretion and TNF-alpha mRNA expression than BCG. Mycobacterium-induced activation of apoptotic gene expression was determined over a time course of infection. M. leprae reduced Bad and Bak mRNA expression by 18 h post-stimulation, with a further decrease at 48 h. Outcome of cell viability is determined by the ratio between pro- and anti-apoptotic proteins present in the cell. M. leprae infection resulted in downregulation of gene expression ratios, Bad/Bcl-2 mRNA by 39% and Bak/Bcl-2 mRNA by 23%. In contrast, live BCG increased Bad/Bcl-2 mRNA (29 %) but had a negligible effect on Bak/Bcl-2 mRNA. Heat killed BCG induced only a negligible (1–4 %) change in mRNA expression of either Bak/Bcl-2 or Bad/Bcl-2. Additionally, M. leprae upregulated the expression of anti-apoptotic gene Mcl-1 while, BCG downregulated Mcl-1 mRNA.

Conclusion

This study proposes an association between mycobacterium-induced apoptosis in THP-1 cells and the regulation of Bcl-2 family of proteins. M. leprae restricts apoptosis in THP-1 cells by downregulation of Bad and Bak and upregulation of Mcl-1 mRNA expression.

Mycobacterium bovis bacille Calmette Guerin infection of human neutrophils induces CXCL8 secretion by MyD88-dependent TLR2 and TLR4 activation

To investigate the potential role of neutrophils in initiation of immune responses to mycobacteria, we have characterized the response of human neutrophils to infection with Mycobacterium bovis bacille Calmette Guerin, the BCG vaccine. BCG induced transcription and secretion of the chemokine CXCL8, by signalling through Toll-like receptors TLR2 and TLR4, in conjunction with the adaptor protein myeloid differentiation factor 88 (MyD88). Blocking of responses with antibodies revealed a difference in the kinetics of signalling through the different TLRs. Anti-TLR2 antibody blocked the early phase of CXCL8 and MyD88 induction. Anti-TLR4 antibody blocked the late phase of induction occurring 2 h after infection. The existence of a TLR/MyD88 pathway for recognition and response to mycobacterial ligands provides neutrophils with the ability to drive the recruitment and activation of inflammatory cells during the early phase of mycobacterial infection and immunization.

Induction of murine macrophage TNF-alpha synthesis by Mycobacterium avium is modulated through complement-dependent interaction via complement receptors 3 and 4 in relation to M. avium glycopeptidolipid

We studied whether complement receptor (CR) mediated Mycobacterium avium interaction modulated macrophage TNF-alpha expression. Compared to control conditions, infections performed with C3-depletion yielded significantly higher TNF-alpha levels. Blockage of the CR4 iC3b site yielded increases in TNF-alpha for all morphotypic variants of a virulent serovar-8 strain (smooth transparent (SmT), smooth opaque (SmO), serovar-specific glycopeptidolipid (ssGPL) deficient knockout mutant) whereas CR3 blockage increased TNF-alpha only for SmT and ssGPL-deficient strains. Thus, complement-mediated binding of M. avium to CR3 and CR4 was shown to modulate TNF-alpha expression. The differential activation of morphotypic and isogenic variants of a single strain provides an excellent model system to delineate signaling pathways.

Elevated ex vivo monocyte chemotactic protein-1 (CCL2) in pulmonary as compared with extra-pulmonary tuberculosis

Background

Tuberculosis causes 3 million deaths annually. The most common site of tuberculosis is pulmonary however; extra-pulmonary forms of the disease also remain prevalent. Restriction of Mycobacterium tuberculosis depends on effective recruitment and subsequent activation of T lymphocytes, mononuclear and polymorphonuclear cells to the site of infection. Tumor necrosis factor (TNF)-α is essential for granuloma formation and is a potent activator of monocyte chemotactic protein (MCP-1, CCL2). CCL2 is essential for recruitment of monocytes and T cells and has been shown to play a role in protection against tuberculosis. Interleukin -8 (CXCL8) is a potent activator of neutrophils. Increased levels of CCL2, CXCL8 and TNFα are reported in tuberculosis but their significance in different forms of tuberculosis is as yet unclear. We have used an ex vivo assay to investigate differences in immune parameters in patients with either pulmonary or extra-pulmonary tuberculosis.

Methods

Serum levels of CCL2, CXCL8 and TNFα were measured in patients with pulmonary tuberculosis (N = 12), extra-pulmonary tuberculosis (N = 8) and BCG-vaccinated healthy volunteers (N = 12). Whole blood cells were stimulated with non-pathogenic Mycobacterium bovis bacille-Calmette Guerin (BCG) vaccine strain or bacterial lipopolysaccharide (LPS) and cyto/chemokines were monitored in supernatants.

Results

Circulating serum levels of CXCL8 and TNFα were raised in all tuberculosis patients, while CCL2 levels were not. There was no difference in spontaneous cytokine secretion from whole blood cells between patients and controls. M. bovis BCG-induced ex vivo CCL2 secretion was significantly greater in pulmonary as compared with both extra-pulmonary tuberculosis patients and endemic controls. In response to LPS stimulation, patients with pulmonary tuberculosis showed increased CCL2 and TNFα responses as compared with the extra-pulmonary group. BCG-, and LPS-induced CXCL8 secretion was comparable between patients and controls.

Conclusion

CCL2 is activated by TNFα and is essential for recruitment of monocytes and T cells to the site of mycobacterial infection. Increased CCL2 activation in pulmonary tuberculosis may result in a stronger cellular response as compared with extra-pulmonary tuberculosis patients, and this may contribute to the localization of infection to the pulmonary site.

Interleukin-8 is differentially expressed by human-derived monocytic cell line U937 infected with Mycobacterium tuberculosis H37Rv and Mycobacterium marinum

Although Mycobacterium marinum is closely related to Mycobacterium tuberculosis H37Rv genomically, the clinical outcome in humans is quite different for M. marinum and M. tuberculosis infections. We investigated possible factors in the host macrophages for determining differential pathological responses to M. tuberculosis and M. marinum using an in vitro model of mycobacterial infection. Using suppression-subtractive hybridization, we identified 12 differentially expressed genes in the human monocytic cell line U937 infected with M. tuberculosis and M. marinum. Of those genes, the most frequently recovered transcript encoded interleukin-8 (IL-8). Northern hybridization revealed that IL-8 mRNA was highly upregulated in M. tuberculosis-infected U937 cells compared with M. marinum-infected cells. In addition, enzyme-linked immunosorbent assay showed that IL-8 protein secretion was significantly elevated in M. tuberculosis-infected U937 cells, human primary monocytes, and monocyte-derived macrophages compared with that in M. marinum-infected cells. The depressed IL-8 expression was unique in M. marinum-infected cells compared with cells infected with other strains of mycobacteria, including M. tuberculosis H37Ra, Mycobacterium bovis BCG, or Mycobacterium smegmatis. When the expression of NF-kappaB was assessed in mycobacterium-infected U937 cells, IkappaBalpha proteins were significantly degraded in M. tuberculosis-infected cells compared with M. marinum-infected cells. Collectively, these results suggest that differential IL-8 expression in human macrophages infected with M. tuberculosis and M. marinum may be critically associated with distinct host responses in tuberculosis. Additionally, our data indicate that differential signal transduction pathways may underlie the distinct patterns of IL-8 secretion in cells infected by the two mycobacteria.