Innate Lymphoid Cells and Their Role in the Immune Response to Infections

Over the past decade, a group of lymphocyte-like cells called innate lymphoid cells (ILCs) has gained considerable attention due to their crucial role in regulating immunity and tissue homeostasis. ILCs, lacking antigen-specific receptors, are a group of functionally differentiated effector cells that act as tissue-resident sentinels against infections. Numerous studies have elucidated the characteristics of ILC subgroups, but the mechanisms controlling protective or pathological responses to pathogens still need to be better understood. This review summarizes the functions of ILCs in the immunology of infections caused by different intracellular and extracellular pathogens and discusses their possible therapeutic potential.

Cytokine Biosignature of Active and Latent Mycobacterium Tuberculosis Infection in Children

None of the currently used diagnostic tools are efficient enough in diagnosing Mycobacterium tuberculosis (M.tb) infection in children. The study was aimed to identify cytokine biosignatures characterizing active and latent tuberculosis (TB) in children. Using a multiplex bead-based technology, we analyzed the levels of 53 Th17-related cytokines and inflammatory mediators in sera from 216 BCG-vaccinated children diagnosed with active TB (TB) or latent TB (LTBI) as well as uninfected controls (HC). Children with active TB, compared to HC children, showed reduced serum levels of IL-17A, MMP-2, OPN, PTX-3, and markedly elevated concentrations of APRIL/TNFSF13. IL-21, sCD40L, MMP-2, and IL-8 were significantly differentially expressed in the comparisons between groups: (1) HC versus TB and LTBI (jointly), and (2) TB versus LTBI. The panel consisting of APRIL/TNFSF13, sCD30/TNFRSF8, IFN-α2, IFN-γ, IL-2, sIL-6Rα, IL-8, IL-11, IL-29/IFN-λ1, LIGHT/TNFSF14, MMP-1, MMP-2, MMP-3, osteocalcin, osteopontin, TSLP, and TWEAK/TNFSF12 possessed a discriminatory potential for the differentiation between TB and LTBI children. Serum-based host biosignatures carry the potential to aid the diagnosis of childhood M.tb infections. The proposed panels of markers allow distinguishing not only children infected with M.tb from uninfected individuals but also children with active TB from those with latent TB.

IL-18/IL-37/IP-10 signalling complex as a potential biomarker for discriminating active and latent TB

Background

Currently, there are serious limitations in the direct diagnosis of active tuberculosis (ATB). We evaluated the levels of the IL-18/IL-37/IP-10 signalling complex proteins in Mycobacterium tuberculosis (M.tb)-specific antigen-stimulated QuantiFERON® Gold In-Tube (QFT) cultures and in serum samples from ATB patients, healthy individuals with latent M.tb infection (LTBI) and healthy controls (HC) to examine whether combined analyses of these proteins were useful in the differentiation of M.tb states.

Methods

The concentrations of IL-18, IL-18BP, IFN-γ, IL-37 and IP-10 in the serum and QFT supernatants were measured using specific enzyme-linked immunosorbent assay (ELISA) kits. Free IL-18 levels were calculated using the law of mass action.

Results

Increased concentrations of total and free IL-18, IL-18BP, IFN-γ and IP-10 in the sera of ATB patients were detected. These increases were not counterbalanced by the overproduction of IL-37. Complex co-expression of serum IL-18BP and IL-37, IP-10 and IFN-γ was identified as the highest discriminative biomarker set for the diagnosis of ATB.

Conclusions

Our results suggest that the IL-18 signalling complex might be exploited by M. tuberculosis to expand the clinical manifestations of pulmonary TB. Therefore, direct analysis of the serum components of the IL-18/IL-37 signalling complex and IP-10 may be applicable in designing novel diagnostic tests for ATB.

Lack of significant effect of interleukin-18 gene variants on tuberculosis susceptibility in the Polish population

BACKGROUND

Polymorphisms in genes encoding cytokines are known to determine susceptibility to Mycobacterium tuberculosis (M.tb) infection. In particular, interleukin-18 (IL-18), an inducer of interferon-gamma (IFN-γ), playing an important role in anti-mycobacterial immune responses, may influence the risk of developing active tuberculosis (TB).

AIM

A case-control study was performed to investigate whether two promoter polymorphisms of the IL-18 gene at positions -137G/A (rs187238) and -607A/C (rs1946518) affect the serum level of IL-18 and might be associated with genetic susceptibility to tuberculosis (TB) in the Polish population.

METHODS

Two IL-18 gene promoter SNPs were detected by an allele-specific polymerase chain reaction. Serum IL-18 levels were measured immunoenzymatically using Human Total IL-18 ELISA DuoSet.

RESULTS

A single-gene analysis showed no differences either in allele or genotype frequencies of the studied SNPs between TB patients and healthy controls. No significant differences in the frequencies of any of the haplotypes between TB patients and healthy controls were found. None of the polymorphic variants of IL-18(-137G/A) or IL-18(-607A/C) SNP was associated with IL-18 producing capability.

CONCLUSION

Our results suggest that IL-18(-137G/A) and IL-18(-607A/C) polymorphisms may not be risk factors for susceptibility to TB in the Polish population. Increased serum IL-18 level observed in TB patients has no genetic background, but is a consequence of M.tb infection. Further studies with a higher sample size are required to confirm these findings.

Mycobacteria-derived biomarkers for tuberculosis diagnosis

Tuberculosis (TB) remains an escalating problem worldwide. The current diagnostic methods do not always guarantee reliable diagnosis. TB treatment is a time-consuming process that requires the use of several chemotherapeutics, to which mycobacteria are becoming increasingly resistant. This article focuses on the potential utility of biomarkers of mycobacterial origin with potential implications for TB diagnosis. Properly standardized indicators could become new diagnostic tools, improving and streamlining the identification of Mycobacterium tuberculosis infection and the implementation of appropriate therapy. These markers can also potentially provide a quick confirmation of effectiveness of new anti-mycobacterial drugs and TB vaccines, leading to a possible application in practice.

Diversity and Functionality of Mycobacterial Mycolic Acids in Relation to Host-pathogen Interactions

BACKGROUND

The complex architecture of the mycobacterial cell wall is responsible for many physiological and infection-associated properties of these pathogens. Long chain mycolic acids with chiral functional groups constitute a major lipid envelope component, and therefore play a crucial role in determining the permeability and fluidity of the cell wall. Varying proportions of the different mycolate types are present in various mycobacteria. This serves to designate a specific mycolic acid profile, allowing the differentiation of species and subspecies.

OBJECTIVE

In this review, we explore the diversity in mycolic acid chemical structure, its influence on cell wall permeability and consequences for virulence, and present how they might be exploited as research targets in diagnosis and chemotherapy.

METHODS

The search of bibliographic databases for adequate, informative and valuable peerreviewed literature was undertaken. The proper papers were identified by the hand and electronic searching through the relevant to the topic-leading journals, key words, named authors, reference scanning, etc.

RESULTS

The review is based on the ninety two carefully selected articles that allow this review to provide up-to-date information. Twenty nine papers were published within last 5 years, including 10 showed up in 2016-2017.

CONCLUSION

The revision of the relevant literature showed that mycolic acids played a crucial role in host-pathogen interactions and thus might serve as a promising tool for differentiation of mycobacterial species and discovering novel tuberculocidal therapeutic strategies.

Interleukin 18 (IL-18) as a target for immune intervention

Interleukin 18 (IL-18) is a pleiotropic cytokine involved in the regulation of innate and acquired immune response. In the milieu of IL-12 or IL-15, IL-18 is a potent inducer of IFN-gamma in natural killer (NK) cells and CD4 T helper (Th) 1 lymphocytes. However, IL-18 also modulates Th2 and Th17 cell responses, as well as the activity of CD8 cytotoxic cells and neutrophils, in a host microenvironment-dependent manner. It is produced by various hematopoietic and nonhematopoietic cells, including dendritic cells and macrophages. In an organism, bioactivity of the cytokine depends on the intensity of IL-18 production, the level of its natural inhibitory protein - IL-18BP (IL-18 binding protein) and the surface expression of IL-18 receptors (IL-18R) on the responding cells. This review summarizes the biology of the IL-18/IL-18BP/IL-18R system and its role in the host defense against infections. The prospects for IL-18 application in immunotherapeutic or prophylactic interventions in infectious and non-infectious diseases are discussed.

The balance between pro- and anti-inflammatory cytokines in the immune responses to BCG and DTwP vaccines

Bacillus Calmette-Guérin (BCG) and pertussis vaccines have been found to be insufficient and their further improvement is required. In order to develop improved vaccines, a better understanding of the main pathways involved in the host's protective immunity to the pathogens is crucial. We address the question as to whether the balance between pro- and anti-inflammatory cytokine production might affect the host responses to BCG and diphtheria-tetanus toxoids-whole cell pertussis (DTwP) vaccines. The study population consisted of 118 healthy people, age range 18-30 years, who had been subjected to BCG and DTwP vaccination according to the state policy. Tuberculin skin testing (TST) revealed a delayed type hypersensitivity (DTH) to PPD (purified protein derivative) in 53% volunteers. The variability in development of the BCG-driven DTH to tuberculin prompted us to address a question as to whether Th1/Th2 polarization is involved in the lack of skin responsiveness to PPD. PPD-stimulated blood lymphocytes from TST(+) participants produced significantly more IFN-γ and less IL-10 than lymphocytes from TST(-) volunteers. However, TST(-) volunteers' sera contained more anti-pertussis IgG but not anti-diphtheria toxin IgG. Mycobacterial antigens and particularly PPD induced a higher expression of HLA-DR and co-stimulatory CD80 receptors on DCs from TST(+) than TST(-) participants. BCG but not PPD pulsed DCs from TST(-) volunteers produced significantly more IL-10. Mycobacterial antigen stimulated DCs from TST(+) volunteers induced a more intense IFN-γ production in co-cultures with autologous lymphocytes than the cells from TST(-) participants. Differences among the types of dendritic cell activities contribute to development of tuberculin reactivity in BCG vaccinated volunteers.

Immune response gene polymorphisms in tuberculosis

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (M.tb), remains a leading public health problem in most parts of the world. Despite the discovery of the bacilli over 100 years ago, there are still many unanswered questions about the host resistance to TB. Although one third of the world's population is infected with virulent M.tb, no more than 5-10% develop active disease within their lifetime. A lot of studies suggest that host genetic factors determine the outcome of M.tb-host interactions, however, specific genes and polymorphisms that govern the development of TB are not completely understood. Strong evidence exists for genes encoding pattern recognition receptors (TLR, CD14), C-type lectins, cytokines/chemokines and their receptors (IFN-γ, TNF-α, IL-12, IL-10, MCP-1, MMP-1), major histocompatibility complex (MHC) molecules, vitamin D receptor (VDR), and proton-coupled divalent metal ion transporters (SLC11A1). Polymorphisms in these genes have a diverse influence on the susceptibility to or protection against TB among particular families, ethnicities and races. In this paper, we review recent discoveries in genetic studies and correlate these findings with their influence on TB susceptibility.