Secretory leukocyte protease inhibitor: a secreted pattern recognition receptor for mycobacteria

The Role of Recombinant Secretory Leukocyte Protease Inhibitor to CD163, FGF-2, IL-1 and IL-6 Expression in Skin Wound Healing

Background

The wound healing process can be optimized through the addition of a biomaterial such as recombinant secretory leukocyte protease inhibitor (rSLPI). The SLPI is a non-glycosylated proteomic material that inhibits protease enzymes and has anti-inflammatory properties, thus accelerating wound healing. This study analyzed the administration of rSLPI doses 0.04 cc and 0.06 cc in skin wound healing on the CD163 expression of macrophages and cytokines such as interleukin 1 (IL-1), interleukin 6 (IL-6) and fibroblast growth factor 2 (FGF-2).

Materials and Methods

rSLPI produced from Escherichia coli TOP10 as the cloning host, BL21 (DE3) strains as the expression host and pET30a plasmids were used for the expression system construction. The wound was created on Wistar rat dorsal skin, then rSLPI 0.04 cc and 0.06 cc was administered. In the next four days, the back skin was biopsied and stained by immunohistochemistry to analyze the CD163, FGF-2, IL-1 and IL-6 expression.

Results

The administration of rSLPI increased CD163 and FGF-2 expression dependent on dose (p<0.05). On the other hand, administration of rSLPI decreased IL-1 and IL-6 expression depending on dose (p <0.05).

Conclusion

The administration of rSLPI is able to accelerate the wound healing process by increasing the CD163 and FGF-2 expression. The cytokines such as IL-1 and IL-6 decreased depending on rSLPI doses.

Time-Course Transcriptome Analysis of Lungs From Mice Infected With Hypervirulent Klebsiella pneumoniae via Aerosolized Intratracheal Inoculation

Hypervirulent Klebsiella pneumoniae (hvKp) can cause life-threatening community-acquired infections among healthy young individuals and is thus of concern for global dissemination. In this study, a mouse model of acute primary hvKp pneumonia was established via aerosolized intratracheal (i.t.) inoculation, laying the foundation for conducting extensive studies related to hvKp. Subsequently, a time-course transcriptional profile was created of the lungs from the mouse model at 0, 12, 24, 48 and 60 hours post-infection (hpi) using RNA Sequencing (RNA-Seq). RNA-Seq data were analyzed with the use of Mfuzz time clustering, weighted gene co-expression network analysis (WGCNA) and Immune Cell Abundance Identifier for mouse (ImmuCellAI-mouse). A gradual change in the transcriptional profile of the lungs was observed that reflected expected disease progression. At 12 hpi, genes related to acute phase inflammatory response increased in expression and lipid metabolism appeared to have a pro-inflammatory effect. At 24 hpi, exacerbation of inflammation was observed and active IFN-γ suggested that signaling promoted activation and recruitment of macrophages occurred. Genes related to maintaining the structural integrity of lung tissues showed a sustained decrease in expression after infection and the decrease was especially marked at 48 hpi. TNF, IL-17, MAPK and NF-kB signaling pathways may play key roles in the immunopathogenesis mechanism at all stages of infection. Natural killer (NK) cells consistently decreased in abundance after infection, which has rarely been reported in hvKp infection and could provide a new target for treatment. Genes Saa1 and Slpi were significantly upregulated during infection. Both Saa1, which is associated with lipopolysaccharide (LPS) that elicits host inflammatory response, and Slpi, which encodes an antimicrobial protein, have not previously been reported in hvKp infections and could be important targets for subsequent studies. To t our knowledge, this paper represents the first study to investigate the pulmonary transcriptional response to hvKp infection. The results provide new insights into the molecular mechanisms underlying the pathogenesis of hvKp pulmonary infection that can contribute to the development of therapies to reduce hvKp pneumonia.

Modulation of Host Immune Response during Leishmania infantum Natural Infection: A Whole-Transcriptome Analysis of the Popliteal Lymph Nodes in Dogs

Leishmania infantum, the etiological agent of canine leishmaniosis (CanL) in Europe, was responsible of the largest outbreak of human leishmaniosis in Spain. The parasite infects and survives within myeloid lineage cells, causing a potentially fatal disease if left untreated. The only treatment option relies on chemotherapy, although immunotherapy strategies are being considered as novel approaches to prevent progression of the disease. To this aim, a deeper characterization of the molecular mechanisms behind the immunopathogenesis of leishmaniosis is necessary. Thus, we evaluated, for the first time, the host immune response during L. infantum infection through transcriptome sequencing of the popliteal lymph nodes aspirates of dogs with CanL. Differential expression and weighted gene co-expression network analyses were performed, resulting in the identification of 5,461 differentially expressed genes (DEGs) and four key modules in sick dogs, compared to controls. As expected, defense response was the highest enriched biological process in the DEGs, with six genes related to immune response against pathogens (CHI3L1, SLPI, ACOD1, CCL5, MPO, BPI) included among the ten most expressed genes; and two of the key co-expression modules were associated with regulation of immune response, which also positively correlated with clinical stage and blood monocyte concentration. In particular, sick dogs displayed significant changes in the expression of Th1, Th2, Th17 and Tr1 cytokines (e. g. TNF-α, IFN-γ, IL-21, IL-17, IL-15), markers of T cell and NK cell exhaustion (e. g. LAG3, CD244, Blimp-1, JUN), and B cell, monocyte and macrophage disrupted functionality (e. g. CD40LG, MAPK4, IL-1R, NLRP3, BCMA). In addition, we found an overexpression of XBP1 and some other genes involved in endoplasmic reticulum stress and the IRE1 branch of the unfolded protein response, as well as one co-expression module associated with these processes, which could be induced by L. infantum to prevent host cell apoptosis and modulate inflammation-induced lymphangiogenesis at lymph nodes. Moreover, 21 lncRNAs were differentially expressed in sick dogs, and one key co-expression module was associated with chromatin organization, suggesting that epigenetic mechanisms could also contribute to dampening host immune response during natural L. infantum infection in the lymph nodes of dogs suffering from clinical leishmaniosis.

Effects of Mycobacterium vaccae vaccine in a mouse model of tuberculosis: protective action and differentially expressed genes

BACKGROUND

Tuberculosis is a leading cause of death worldwide. BCG is an effective vaccine, but not widely used in many parts of the world due to a variety of issues. Mycobacterium vaccae (M. vaccae) is another vaccine used in human subjects to prevent tuberculosis. In the current study, we investigated the potential mechanisms of M. vaccae vaccination by determining differentially expressed genes in mice infected with M. tuberculosis before and after M. vaccae vaccination.

METHODS

Three days after exposure to M. tuberculosis H37Rv strain (5 × 10⁵ CFU), adult BALB/c mice randomly received either M. vaccae vaccine (22.5 μg) or vehicle via intramuscular injection (n = 8). Booster immunization was conducted 14 and 28 days after the primary immunization. Differentially expressed genes were identified by microarray followed by standard bioinformatics analysis.

RESULTS

M. vaccae vaccination provided protection against M. tuberculosis infection (most prominent in the lungs). We identified 2326 upregulated and 2221 downregulated genes in vaccinated mice. These changes could be mapped to a total of 123 signaling pathways (68 upregulated and 55 downregulated). Further analysis pinpointed to the MyD88-dependent TLR signaling pathway and PI3K-Akt signaling pathway as most likely to be functional.

CONCLUSIONS

M. vaccae vaccine provided good protection in mice against M. tuberculosis infection, via a highly complex set of molecular changes. Our findings may provide clue to guide development of more effective vaccine against tuberculosis.

Plasma concentrations of secretory leukocyte protease inhibitor (SLPI) differ depending on etiology and severity in community-onset bloodstream infection

The severity of bloodstream infections (BSI) depends on pathogen, source, and host factors. Secretory leukocyte protease inhibitor (SLPI) counteracts tissue damage, balances inflammation, and is increased in pneumonia and sepsis. We aimed to evaluate whether SLPI production differs depending on etiology, disease severity, and sex in BSI and to correlate SLPI with markers of inflammation and immunosuppression. Of the adult patients with BSI, 109 were included and sampled repeatedly, from hospital admission through day 28. Controls (blood donors) were sampled twice. SLPI in plasma was measured with enzyme-linked immunosorbent assay (ELISA) technique. Streptococcus pneumoniae and Staphylococcus aureus etiology were associated with higher SLPI than Escherichia coli on days 1–2 and 3. On day 1–2, subjects with sepsis had higher SLPI concentrations than those with non-septic BSI. Pneumonia was associated with higher SLPI than a non-pulmonary source of infection. SLPI co-varied with inflammatory markers. SLPI concentrations did not differ with regard to sex in the full cohort, but men with pneumonia had higher SLPI than women on day 1–2. S. pneumoniae and S. aureus BSI were associated with higher SLPI, when compared to E. coli. Severity and pneumonia, as well as male sex in the pneumonia sub-cohort, were factors independently associated with higher SLPI.

Cementoin-SLPI fusion protein binds to human monocytes and epithelial cells and shows higher biological activity than SLPI

Secretory Leukocyte Proteinase Inhibitor (SLPI) is an antiinflammatory peptide that blocks the activity of serine proteases, primarily the neutrophil elastase. In an attempt to direct the activity of SLPI on inflamed sites, a chimera consisting of the transglutaminase II substrate domain of trappin 2 (cementoin), and the mature SLPI protein was constructed. Cell attachment and biological activity were compared between SLPI and this chimera. By using whole cell ELISA, fluorescence microscopy and flow cytometry assays we observed that the cementoin-SLPI fusion protein (FP) but not SLPI attached to a human lung epithelial cell line and monocytes. A maximum attachment was achieved 15 min after FP was added to the cell cultures. In an elastase activity assay, we observed that FP retained its antiprotease activity and that at equimolar amount of proteins, FP was more efficient than SLPI in the inhibition. Both, FP and SLPI inhibits IL-2-induced lymphocyte proliferation, however, lower amounts of FP were required to achieve this inhibition. Furthermore, FP binds to mycobacteria and maintained the bactericidal activity observed for SLPI. Overall, these results show that this new chimera is able to attach to the cell surfaces retaining and improving some biological activities described for SLPI.

RNAseq reveals hypervirulence-specific host responses to M. tuberculosis infection

The distinguishing factors that characterize the host response to infection with virulent Mycobacterium tuberculosis (M.tb) are largely confounding. We present an infection study with 2 genetically closely related M.tb strains that have vastly different pathogenic characteristics. The early host response to infection with these detergent-free cultured strains was analyzed through RNAseq in an attempt to provide information on the subtleties which may ultimately contribute to the virulent phenotype. Murine bone marrow derived macrophages (BMDMs) were infected with either a hyper- (R5527) or hypovirulent (R1507) Beijing M. tuberculosis clinical isolate. RNAseq revealed 69 differentially expressed host genes in BMDMs during comparison of these 2 transcriptomes. Pathway analysis revealed activation of the stress-induced and growth inhibitory Gadd45 signaling pathway in hypervirulent infected BMDMs. Upstream regulators of interferon activation such as and IRF3 and IRF7 were predicted to be upregulated in hypovirulent-infected BMDMs. Additional analysis of the host immune response through ELISA and qPCR included the use of human THP-1 macrophages where a robust proinflammatory response was observed after infection with the hypervirulent strain. RNAseq revealed 2 early-response genes (ier3 and saa3) and 2 host-defense genes (oasl1 and slpi) that were significantly upregulated by the hypervirulent strain. The role of these genes under M.tb infection conditions are largely unknown but here we provide validation of their presence with use of qPCR and Western blot. Further analysis into their biological role during infection with virulent M.tb is required.

Serum alarm antiproteases in systemic sclerosis patients

Alarm antiproteases, i.e. secretory leukocyte protease inhibitor ad elafin, are key mediators in innate immune response and integrate innate and adaptive immunity systems. The aim of the study was to assess clinical significance of serum levels of alarm antiproteases, elafin and secretory leukocyte protease inhibitor (SLPI) in patients with systemic sclerosis (SSc). Twenty-eight patients with SSc, 25 patients with rheumatoid arthritis (RA) and 22 healthy controls were recruited. Serum elafin and SLPI levels were examined using enzyme-linked immunosorbent assay (ELISA). The patients with SSc had significantly increased serum levels of SLPI in comparison with the RA patients and the healthy controls (p<0.01), and the RA patients presented significantly higher serum levels of elafin in comparison with the controls (p=0.003). In the SSc subgroup serum SLPI level negatively correlated with diffusing capacity of the lung for carbon monoxide (DLCO) (r=-0.41, p=0.03) and total lung capacity (r=-0.42, p=0.03). Both alarm antiproteases, elafin and SLPI could be potentially implicated in the pathogenesis of SSc and SLPI may be considered a candidate for serum biomarker of lung involvement in SSc.

Secretory leukocyte protease inhibitor promising protective roles in obesity-associated atherosclerosis

Secretory leukocyte protease inhibitor (SLPI), a serine protease inhibitor, which was most commonly examined in mucosal fluids such as saliva, is a versatile molecule and plays non-redundant roles. In addition to its anti-protease activity, SLPI has been shown to express anti-bacterial, anti-viral, anti-fungal, and anti-inflammatory properties as well as participating in innate and adaptive immune responses, most of which has been well documented. Recently, it is reported that SLPI is expressed in adipocytes and adipose tissue where it could play an important feedback role in the resolution of inflammation. Furthermore, circulating SLPI has been shown to correlate with progressive metabolic dysfunction. Moreover, adenoviral gene delivery of elafin and SLPI attenuates nuclear factor-κB-dependent inflammatory responses of human endothelial cells and macrophages to atherogenic stimuli. This review contributes to unraveling the protective role of SLPI in obesity-related atherosclerosis development, and the potential role in preventing arterial plaque rupture.

Secretory leukocyte protease inhibitor (SLPI), a multifunctional protein in the host defense response

Secretory leukocyte protease inhibitor (SLPI), a ∼12kDa nonglycosylated cationic protein, is emerging as an important regulator of innate and adaptive immunity and as a component of tissue regenerative programs. First described as an inhibitor of serine proteases such as neutrophil elastase, this protein is increasingly recognized as a molecule that benefits the host via its anti-proteolytic, anti-microbial and immunomodulatory activities. Here, we discuss the diverse functions of SLPI. Moreover, we review several novel layers of SLPI-mediated control that protect the host from excessive/dysregulated inflammation typical of infectious, allergic and autoinflammatory diseases and that support healing responses through affecting cell proliferation, differentiation and apoptosis.

Hypoxia down-regulates expression of secretory leukocyte protease inhibitor in bronchial epithelial cells via TGF-β1

Background

Secretory leukocyte protease inhibitor (SLPI) is a protein with anti-protease and antimicrobial properties that is constitutively secreted from the airway epithelium. The importance of maintaining a balance between proteases and anti-proteases, and robust innate defence mechanisms in the airways, is exemplified by inflammatory lung conditions such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF). Both conditions present with a high protease burden in the airways which leads to tissue destruction. These patients also have an impaired innate immune system in the lungs with bacterial colonization and frequent airway infections. Moreover, both diseases are associated with airway hypoxia due to inflammation and mucus plugs. The aim of the present study was to investigate the role of hypoxia on SLPI production from the airway epithelium.

Methods

Primary human bronchial epithelial cells were grown in sub-immersed cultures or as differentiated epithelium in air liquid interface cultures. Cells were incubated at 21% O₂ (normoxia) or 1% O₂ (hypoxia), and the release of SLPI was analysed with ELISA. RT-PCR was used to study the expression of SLPI and transforming growth factor β1 (TGF-β1).

Results

Hypoxia decreased the constitutive production of SLPI by bronchial epithelial cells. The multifunctional cytokine TGF-β1, which is known to affect SLPI expression, showed increased expression in hypoxic bronchial epithelial cells. When bronchial epithelial cells were exposed to exogenous TGF-β1 during normoxia, the SLPI production was down-regulated. Addition of TGF-β1-neutralizing antibodies partially restored SLPI production during hypoxia, showing that TGF-β1 is an important regulator of SLPI during hypoxic conditions.

Conclusions

The mechanism described here adds to our knowledge of the pathogenesis of severe pulmonary diseases associated with hypoxia, e.g. COPD and CF. The hypoxic down-regulation of SLPI may help explain the protease/anti-protease imbalance associated with these conditions and vulnerability to airway infections. Furthermore, it provides an interesting target for the treatment and prevention of exacerbation in these patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12890-015-0016-0) contains supplementary material, which is available to authorized users.

Secretory Leukocyte Protease Inhibitor (SLPI): Emerging Roles in CNS Trauma and Repair

At first glance, secretory leukocyte protease inhibitor (SLPI) would appear to have little relevance to the central nervous system (CNS). This serine protease inhibitor is most commonly found in mucosal fluids such as saliva and is best known for its anti-inflammatory and antimicrobial properties. It has been shown to promote wound healing by reducing expression of pro-inflammatory cytokines, and it can also inhibit bacterial growth and block HIV infection of macrophages. In the past 10 years, however, several studies have reported that SLPI is strongly up-regulated in response to CNS injury and that exogenous administration of SLPI is neuroprotective. It has also been shown that SLPI can overcome inhibition by CNS myelin and promote axonal regeneration. In this review, we will discuss these studies, examine the molecular mechanisms underlying SLPI's effects, and consider SLPI's potential for therapeutic use in cerebral ischemia, spinal cord injury, and multiple sclerosis.

Outcome of Mycobacterium tuberculosis and Toll-like receptor interaction: immune response or immune evasion?

Mycobacterium tuberculosis (M. tuberculosis), the causative agent of tuberculosis, is an intracellular bacterium capable of surviving and persisting within host mononuclear cells. The host response against tubercle bacilli is dominated by fine-tuned interaction of innate and adaptive immune responses. Toll-like receptors (TLRs) play a critical role in the formation of this immune response by facilitating in elaboration of protective T helper type 1 (Th1) cytokines and microbicidal molecules, but the intracellular persistence of M. tuberculosis in the phagosome and processing and presentation of TLR ligands by host antigen-presenting cell leads to continuous and chronic TLR2 signaling. The prolonged stimulation of TLR ultimately results in elaboration of immunosuppressive cytokines and downregulation of antigen presentation by major histocompatibility complex (MHC) class II and therefore becomes beneficial for M. tuberculosis, resulting in its continued survival inside macrophages. An understanding of the host-pathogen interaction in tuberculosis is important to delineate the mechanisms that can modulate the immune response toward protection. This review focuses on the role of TLRs in immune response and immune evasion and how M. tuberculosis maintains its dominance over the host during infection. A precise understanding of the TLRs and M. tuberculosis interaction will undoubtedly lead to the development of novel therapies to combat tuberculosis.

The impact of IFN-γ receptor on SLPI expression in active tuberculosis: association with disease severity

Interferon (IFN)-γ displays a critical role in tuberculosis (TB), modulating the innate and adaptive immune responses. Previously, we reported that secretory leukocyte protease inhibitor (SLPI) is a pattern recognition receptor with anti-mycobacterial activity against Mycobacterium tuberculosis (Mtb). Herein, we determined whether IFN-γ modulated the levels of SLPI in TB patients. Plasma levels of SLPI and IFN-γ were studied in healthy donors (HDs) and TB patients. Peripheral blood mononuclear cells from HDs and patients with TB or defective IFN-γ receptor 1* were stimulated with Mtb antigen and SLPI, and IFN-γR expression levels were measured. Both SLPI and IFN-γ were significantly enhanced in plasma from those with TB compared with HDs. A direct association between SLPI levels and the severity of TB was detected. In addition, Mtb antigen stimulation decreased the SLPI produced by peripheral blood mononuclear cells from HDs, but not from TB or IFN-γR patients. Neutralization of IFN-γ reversed the inhibition of SLPI induced by Mtb antigen in HDs, but not in TB patients. Furthermore, recombinant IFN-γ was unable to modify the expression of SLPI in TB patients. Finally, IFN-γR expression was lower in TB compared with HD peripheral blood mononuclear cells. These results show that Mtb-induced IFN-γ down-modulated SLPI levels by signaling through the IFN-γR in HDs. This inhibitory mechanism was not observed in TB, probably because of the low expression of IFN-γR detected in these individuals.

Anti-tumor effect of SLPI on mammary but not colon tumor growth

Secretory leukocyte protease inhibitor (SLPI) is a serine protease inhibitor that was related to cancer development and metastasis dissemination on several types of tumors. However, it is not known the effect of SLPI on mammary and colon tumors. The aim of this study was to examine the effect of SLPI on mammary and colon tumor growth. The effect of SLPI was tested on in vitro cell apoptosis and in vivo tumor growth experiments. SLPI over-expressing human and murine mammary and colon tumor cells were generated by gene transfection. The administration of murine mammary tumor cells over-expressing high levels of SLPI did not develop tumors in mice. On the contrary, the administration of murine colon tumor cells over-expressing SLPI, developed faster tumors than control cells. Intratumoral, but not intraperitoneal administration of SLPI, delayed the growth of tumors and increased the survival of mammary but not colon tumor bearing mice. In vitro culture of mammary tumor cell lines treated with SLPI, and SLPI producer clones were more prone to apoptosis than control cells, mainly under serum deprivation culture conditions. Herein we demonstrated that SLPI induces the apoptosis of mammary tumor cells in vitro and decreases the mammary but not colon tumor growth in vivo. Therefore, SLPI may be a new potential therapeutic tool for certain tumors, such as mammary tumors.

Secretory leukocyte protease inhibitor binds to Neisseria gonorrhoeae outer membrane opacity protein and is bactericidal

PROBLEM

Secretory leukocyte protease inhibitor (SLPI) is an innate immune peptide present on the genitourinary tract mucosa that has antimicrobial activity. In this study, we investigated the interaction of SLPI with Neisseria gonorrhoeae.

METHOD OF STUDY

ELISA and far-Western blots were used to analyze binding of SLPI to gonococci. The binding site for SLPI was identified by tryptic digests and mass spectrometry. Antimicrobial activity of SLPI for gonococci was determined using bactericidal assays. SLPI protein levels in cell supernatants were measured by ELISA, and SLPI mRNA levels were assessed by quantitative RT-PCR.

RESULTS

SLPI bound directly to the gonococcal Opa protein and was bactericidal. Epithelial cells from the reproductive tract constitutively expressed SLPI at different levels. Gonococcal infection of cells did not affect SLPI expression.

CONCLUSION

We conclude that SLPI is bactericidal for gonococci and is expressed by reproductive tract epithelial cells and thus is likely to play a role in the pathogenesis of gonococcal infection.

WAP domain proteins as modulators of mucosal immunity

WAP (whey acidic protein) is an important whey protein present in milk of mammals. This protein has characteristic domains, rich in cysteine residues, called 4-DSC (four-disulfide core domain). Other proteins, mainly present at mucosal surfaces, have been shown to also possess these characteristic WAP-4-DSC domains. The present review will focus on two WAP-4-DSC containing proteins, namely SLPI (secretory leucocyte protease inhibitor) and trappin-2/elafin. Although first described as antiproteases able to inhibit in particular host neutrophil proteases [NE (neutrophil elastase), cathepsin-G and proteinase-3] and as such, able to limit maladaptive tissue damage during inflammation, it has become apparent that these molecules have a variety of other functions (direct antimicrobial activity, bacterial opsonization, induction of adaptive immune responses, promotion of tissue repair, etc.). After providing information about the 'classical' antiproteasic role of these molecules, we will discuss the evidence pertaining to their pleiotropic functions in inflammation and immunity.

Serine leucocyte proteinase inhibitor-treated monocyte inhibits human CD4(+) lymphocyte proliferation

Serine leucocyte proteinase inhibitor (SLPI) is the main serine proteinase inhibitor produced by epithelial cells and has been shown to be a pleiotropic molecule with anti-inflammatory and microbicidal activities. However, the role of SLPI on the adaptive immune response is not well established. Therefore, we evaluated the effect of SLPI on lymphocyte proliferation and cytokine production. Human peripheral blood mononuclear cells (PBMC) were treated with mitogens plus SLPI and proliferation was assessed by [(3) H]thymidine uptake. The SLPI decreased the lymphocyte proliferation induced by interleukin-2 (IL-2) or OKT3 monoclonal antibodies in a dose-dependent manner. Inhibition was not observed when depleting monocytes from the PBMC and it was restored by adding monocytes and SLPI. SLPI-treated monocyte slightly decreased MHC II and increased CD18 expression, and secreted greater amounts of IL-4, IL-6 and IL-10 in the cell culture supernatants. SLPI-treated monocyte culture supernatant inhibited the CD4(+) lymphocyte proliferation but did not affect the proliferation of CD8(+) cells. Moreover, IL-2 increased T-bet expression and the presence of SLPI significantly decreased it. Finally, SLPI-treated monocyte culture supernatant dramatically decreased interferon-γ but increased IL-4, IL-6 and IL-10 in the presence of IL-2-treated T cells. Our results demonstrate that SLPI target monocytes, which in turn inhibit CD4 lymphocyte proliferation and T helper type 1 cytokine secretion. Overall, these results suggest that SLPI is an alarm protein that modulates not only the innate immune response but also the adaptive immune response.

C-type lectins with a sweet spot for Mycobacterium tuberculosis

The pattern of receptors sensing pathogens onto host cells is a key factor that can determine the outcome of the infection. This is particularly true when such receptors belong to the family of pattern recognition receptors involved in immunity. Mycobacterium tuberculosis, the etiologic agent of tuberculosis interacts with a wide range of pattern-recognition receptors present on phagocytes and belonging to the Toll-like, Nod-like, scavenger and C-type lectin receptor families. A complex scenario where those receptors can establish cross-talks in recognizing pathogens or microbial determinants including mycobacterial components in different spatial and temporal context starts to emerge as a key event in the outcome of the immune response, and thus, the control of the infection. In this review, we will focus our attention on the family of calcium-dependent carbohydrate receptors, the C-type lectin receptors, that is of growing importance in the context of microbial infections. Members of this family appear to be key innate immune receptors of mycobacteria, capable of cross-talk with other pattern recognition receptors to induce or modulate the inflammatory context upon mycobacterial infection.

Innate immune effectors in mycobacterial infection

Tuberculosis, which is caused by infection with Mycobacterium tuberculosis (Mtb), remains one of the major bacterial infections worldwide. Host defense against Mtb is mediated by a combination of innate and adaptive immune responses. In the last 15 years, the mechanisms for activation of innate immunity have been elucidated. Toll-like receptors (TLRs) have been revealed to be critical for the recognition of pathogenic microorganisms including mycobacteria. Subsequent studies further revealed that NOD-like receptors and C-type lectin receptors are responsible for the TLR-independent recognition of mycobacteria. Several molecules, such as active vitamin D₃, secretary leukocyte protease inhibitor, and lipocalin 2, all of which are induced by TLR stimulation, have been shown to direct innate immune responses to mycobacteria. In addition, Irgm1-dependent autophagy has recently been demonstrated to eliminate intracellular mycobacteria. Thus, our understanding of the mechanisms for the innate immune response to mycobacteria is developing.

Secretory leukocyte protease inhibitor and elafin/trappin-2: versatile mucosal antimicrobials and regulators of immunity

Elafin and secretory leukocyte protease inhibitor (SLPI) are pleiotropic molecules chiefly synthesized at the mucosal surface that have a fundamental role in the surveillance against microbial infections. Their initial discovery as anti-proteases present in the inflammatory milieu in chronic pathologies such as those of the lung suggested that they may play a role in keeping in check extracellular proteases released during the excessive activation of innate immune cells such as neutrophils. This soon proved to be a simplistic explanation, as other functions were also soon ascribed to these molecules (antimicrobial, modulation of innate and adaptive immunity, regulation of tissue repair). Data emanating from patients with chronic pathologies (in the lung and elsewhere) have shown that SLPI and elafin are often inactivated in inflammatory secretions, either through the action of host or microbial products, justifying attempts at antiprotease supplementation in clinical protocols. Although these have been sparse, proof of principle has been demonstrated, and future challenges will undoubtedly rest with improvements in methods of delivery in the context of tissue inflammation and in careful selection of patients more likely to benefit from SLPI/elafin augmentation.

Resuscitation-promoting factors reveal an occult population of tubercle Bacilli in Sputum

RATIONALE

Resuscitation-promoting factors (Rpfs) are a family of secreted proteins produced by Mycobacterium tuberculosis (Mtb) that stimulate mycobacterial growth. Although mouse infection studies show that they support bacterial survival and disease reactivation, it is currently unknown whether Rpfs influence human infection. We hypothesized that tuberculous sputum might include a population of Rpf-dependent Mtb cells.

OBJECTIVES

To determine whether Rpf-dependent Mtb cells are present in human sputum and explore the impact of chemotherapy on this population.

METHODS

In tuberculous sputum samples we compared the number of cells detected by conventional agar colony-forming assay with that determined by limiting dilution, most-probable number assay in the presence or absence of Rpf preparations.

MEASUREMENTS AND MAIN RESULTS

In 20 of 25 prechemotherapy samples from separate patients, 80-99.99% of the cells demonstrated by cultivation could be detected only with Rpf stimulation. Mtb cells with this phenotype were not generated on specimen storage or by inoculating sputum samples with a selection of clinical isolates; moreover, Rpf dependency was lost after primary isolation. During chemotherapy, the proportion of Rpf-dependent cells was found to increase relative to the surviving colony-forming population.

CONCLUSIONS

Smear-positive sputum samples are dominated by a population of Mtb cells that can be grown only in the presence of Rpfs. These intriguing proteins are therefore relevant to human infection. The Rpf-dependent population is invisible to conventional culture and is progressively enhanced in relative terms during chemotherapy, indicating a form of phenotypic resistance that may be significant for both chemotherapy and transmission.

Expression and characterization of recombinant human secretory leukocyte protease inhibitor (SLPI) protein from Pichia pastoris

The human secretory leukocyte protease inhibitor (SLPI) has been shown to possess anti-protease, anti-inflammatory and antimicrobial properties. Its presence in saliva is believed to be a major deterrent to oral transmission of human immunodeficiency virus-1. The 11.7kDa peptide is a secreted, nonglycosylated protein rich in disulfide bonds. Currently, recombinant SLPI is only available as an expensive bacterial expression product. We have investigated the utility of the methylotrophic yeast Pichia pastoris to produce and secrete SLPI with C-terminal c-myc and polyhistidine tags. The post-transformational vector amplification protocol was used to isolate strains with increased copy number, and culturing parameters were varied to optimize SLPI expression. Modification of the purification procedure allowed the secreted, recombinant protein to be isolated from the cell-free fermentation medium with cobalt affinity chromatography. This yeast-derived SLPI was shown to have an anti-protease activity comparable to the commercially available bacterial product. Thus, P. pastoris provides an efficient, cost-effective system for producing SLPI for structure function analysis studies as well as a wide array of potential therapeutic applications.