Infections in IFNGR-1-deficient children

Deregulation of interferon-gamma receptor 1 expression and its implications for lung adenocarcinoma progression

Interferon-gamma (IFN-γ) plays a dual role in cancer; it is both a pro- and an antitumorigenic cytokine, depending on the type of cancer. The deregulation of the IFN-γ canonic pathway is associated with several disorders, including vulnerability to viral infections, inflammation, and cancer progression. In particular, the interplay between lung adenocarcinoma (LUAD) and viral infections appears to exist in association with the deregulation of IFN-γ signaling. In this mini-review, we investigated the status of the IFN-γ signaling pathway and the expression level of its components in LUAD. Interestingly, a reduction in IFNGR1 expression seems to be associated with LUAD progression, affecting defenses against viruses such as severe acute respiratory syndrome coronavirus 2. In addition, alterations in the expression of IFNGR1 may inhibit the antiproliferative action of IFN-γ signaling in LUAD.

Post-transcriptional regulatory feedback encodes JAK-STAT signal memory of interferon stimulation

Immune cells fine tune their responses to infection and inflammatory cues. Here, using live-cell confocal microscopy and mathematical modelling, we investigate interferon-induced JAK-STAT signalling in innate immune macrophages. We demonstrate that transient exposure to IFN-γ stimulation induces a long-term desensitisation of STAT1 signalling and gene expression responses, revealing a dose- and time-dependent regulatory feedback that controls JAK-STAT responses upon re-exposure to stimulus. We show that IFN-α/β1 elicit different level of desensitisation from IFN-γ, where cells refractory to IFN-α/β1 are sensitive to IFN-γ, but not vice versa. We experimentally demonstrate that the underlying feedback mechanism involves regulation of STAT1 phosphorylation but is independent of new mRNA synthesis and cognate receptor expression. A new feedback model of the protein tyrosine phosphatase activity recapitulates experimental data and demonstrates JAK-STAT network’s ability to decode relative changes of dose, timing, and type of temporal interferon stimulation. These findings reveal that STAT desensitisation renders cells with signalling memory of type I and II interferon stimulation, which in the future may improve administration of interferon therapy.

RNAi-based modulation of IFN-γ signaling in skin

Aberrant activation of interferon (IFN)-γ signaling plays a key role in several autoimmune skin diseases, including lupus erythematosus, alopecia areata, vitiligo, and lichen planus. Here, we identify fully chemically modified small interfering RNAs (siRNAs) that silence the ligand binding chain of the IFN-γ receptor (IFNGR1), for the modulation of IFN-γ signaling. Conjugating these siRNAs to docosanoic acid (DCA) enables productive delivery to all major skin cell types local to the injection site, with a single dose of injection supporting effective IFNGR1 protein reduction for at least 1 month in mice. In an ex vivo model of IFN-γ signaling, DCA-siRNA efficiently inhibits the induction of IFN-γ-inducible chemokines, CXCL9 and CXCL10, in skin biopsies from the injection site. Our data demonstrate that DCA-siRNAs can be engineered for functional gene silencing in skin and establish a path toward siRNA treatment of autoimmune skin diseases.

Ontogeny of plasma cytokine and chemokine concentrations across the first week of human life

Introduction/background & aims:

Early life is marked by distinct and rapidly evolving immunity and increased susceptibility to infection. The vulnerability of the newborn reflects development of a complex immune system in the face of rapidly changing demands during the transition to extra-uterine life. Cytokines and chemokines contribute to this dynamic immune signaling network and can be altered by many factors, such as infection. Newborns undergo dynamic changes important to health and disease, yet there is limited information regarding human neonatal plasma cytokine and chemokine concentrations over the first week of life. The few available studies are limited by small sample size, cross-sectional study design, or focus on perturbed host states like severe infection or prematurity. To characterize immune ontogeny among healthy full-term newborns, we assessed plasma cytokine and chemokine concentrations across the first week of life in a robust longitudinal cohort of healthy, full-term African newborns.

Methods:

We analyzed a subgroup of a cohort of healthy newborns at the Medical Research Council Unit in The Gambia (West Africa; N = 608). Peripheral blood plasma was collected from all study participants at birth (day of life (DOL) 0) and at one follow-up time point at DOL 1, 3, or 7. Plasma cytokine and chemokine concentrations were measured by bead-based cytokine multiplex assay. Unsupervised clustering was used to identify patterns in plasma cytokine and chemokine ontogeny during early life.

Results:

We observed an increase across the first week of life in plasma Th1 cytokines such as IFNγ and CXCL10 and a decrease in Th2 and anti-inflammatory cytokines such as IL-6 and IL-10, and chemokines such as CXCL8. In contrast, other cytokines and chemokines (e.g. IL-4 and CCL5, respectively) remained unchanged during the first week of life. This robust ontogenetic pattern did not appear to be affected by gestational age or sex.

Conclusions:

Ontogeny is a strong driver of newborn plasma-based levels of cytokines and chemokines throughout the first week of life with a rising IFNγ axis suggesting post-natal upregulation of host defense pathways. Our study will prove useful to the design and interpretation of future studies aimed at understanding the neonatal immune system during health and disease.

Emapalumab in Children with Primary Hemophagocytic Lymphohistiocytosis

BACKGROUND

Primary hemophagocytic lymphohistiocytosis is a rare syndrome characterized by immune dysregulation and hyperinflammation. It typically manifests in infancy and is associated with high mortality.

METHODS

We investigated the efficacy and safety of emapalumab (a human anti-interferon-γ antibody), administered with dexamethasone, in an open-label, single-group, phase 2-3 study involving patients who had received conventional therapy before enrollment (previously treated patients) and previously untreated patients who were 18 years of age or younger and had primary hemophagocytic lymphohistiocytosis. The patients could enter a long-term follow-up study until 1 year after allogeneic hematopoietic stem-cell transplantation or until 1 year after the last dose of emapalumab, if transplantation was not performed. The planned 8-week treatment period could be shortened or extended if needed according to the timing of transplantation. The primary efficacy end point was the overall response, which was assessed in the previously treated patients according to objective clinical and laboratory criteria.

RESULTS

At the cutoff date of July 20, 2017, a total of 34 patients (27 previously treated patients and 7 previously untreated patients) had received emapalumab; 26 patients completed the study. A total of 63% of the previously treated patients and 65% of the patients who received an emapalumab infusion had a response; these percentages were significantly higher than the prespecified null hypothesis of 40% (P = 0.02 and P = 0.005, respectively). In the previously treated group, 70% of the patients were able to proceed to transplantation, as were 65% of the patients who received emapalumab. At the last observation, 74% of the previously treated patients and 71% of the patients who received emapalumab were alive. Emapalumab was not associated with any organ toxicity. Severe infections developed in 10 patients during emapalumab treatment. Emapalumab was discontinued in 1 patient because of disseminated histoplasmosis.

CONCLUSIONS

Emapalumab was an efficacious targeted therapy for patients with primary hemophagocytic lymphohistiocytosis. (Funded by NovImmune and the European Commission; NI-0501-04 and NI-0501-05 ClinicalTrials.gov numbers, NCT01818492 and NCT02069899.).

The monogenic basis of human tuberculosis

The pathogenesis of tuberculosis (TB) remains poorly understood, as no more than 5-10% of individuals infected with Mycobacterium tuberculosis go on developing clinical disease. The contribution of human genetics to TB pathogenesis has been amply documented by means of classic genetics since the turn of the twentieth century. Over the last 20 years, following-up on the study of Mendelian susceptibility to mycobacterial disease (MSMD), monogenic disorders have been found to underlie TB in some patients. Rare inborn errors of immunity, such as autosomal recessive, complete IL-12Rβ1 and TYK2 deficiencies, impairing the IL-12- and IL-23-dependent induction of IFN-γ, were initially identified in a few patients. More recently, homozygosity for a common variant of TYK2 (P1104A) that selectively disrupts cellular responses to IL-23 was found in two cohorts of TB patients. It shows high penetrance in areas endemic for TB and appears to be responsible for about 1% of TB cases in populations of European descent. Both rare and common genetic etiologies of TB affect IFN-γ immunity, providing a rationale for novel preventive and therapeutic approaches for TB control, including the use of recombinant IFN-γ.

Mycobacterium abscessus Infections in Children: A Review of Current Literature

There is limited literature on Mycobacterium abscessus infections in children and limited data about its diagnosis and management. The incidence of infections due to M abscessus appears to be increasing in certain populations and can be a significant cause of morbidity and mortality.Management of these infections is challenging and relies on combination antimicrobial therapy and debridement of diseased tissue, depending on the site and extent of disease. Treatment regimens often are difficult to tolerate, and the antimicrobials used can cause significant adverse effects, particularly given the long duration of therapy needed.This review summarizes the literature and includes information from our own institution's experience on pediatric M abscessus infections including the epidemiology, transmission, clinical manifestations, and the management of these infections. Adult data have been used where there are limited pediatric data. Further studies regarding epidemiology and risk factors, clinical presentation, optimal treatment, and outcomes in children are necessary.

Dominant-negative IKZF1 mutations cause a T, B, and myeloid cell combined immunodeficiency

Ikaros/IKZF1 is an essential transcription factor expressed throughout hematopoiesis. IKZF1 is implicated in lymphocyte and myeloid differentiation and negative regulation of cell proliferation. In humans, somatic mutations in IKZF1 have been linked to the development of B cell acute lymphoblastic leukemia (ALL) in children and adults. Recently, heterozygous germline IKZF1 mutations have been identified in patients with a B cell immune deficiency mimicking common variable immunodeficiency. These mutations demonstrated incomplete penetrance and led to haploinsufficiency. Herein, we report 7 unrelated patients with a novel early-onset combined immunodeficiency associated with de novo germline IKZF1 heterozygous mutations affecting amino acid N159 located in the DNA-binding domain of IKZF1. Different bacterial and viral infections were diagnosed, but Pneumocystis jirovecii pneumonia was reported in all patients. One patient developed a T cell ALL. This immunodeficiency was characterized by innate and adaptive immune defects, including low numbers of B cells, neutrophils, eosinophils, and myeloid dendritic cells, as well as T cell and monocyte dysfunctions. Notably, most T cells exhibited a naive phenotype and were unable to evolve into effector memory cells. Functional studies indicated these mutations act as dominant negative. This defect expands the clinical spectrum of human IKZF1-associated diseases from somatic to germline, from haploinsufficient to dominant negative.

TCR independent suppression of CD8(+) T cell cytokine production mediated by IFNγ in vivo

CD8(+) memory T cells produce IFNγ within hours of secondary infection, but this is quickly terminated in vivo despite the presence of stimulatory viral antigen, suggesting that active suppression occurs. Herein, we investigated the in vivo effector function of CD8(+) memory T cells during successive encounters with viral antigen. CD8(+) T cells in immune mice receiving prior viral or peptide challenge failed to reproduce IFNγ during LCMV rechallenge. Surprisingly, this refractory state was induced even in memory cells that had not encountered their cognate antigen, indicating that the silencing of CD8(+) T cell responses is TCR-independent. Direct injection of IFNγ also suppressed the ability of virus-specific memory cells to respond to subsequent viral challenge. We propose the existence of a negative feedback loop whereby IFNγ, produced by memory CD8(+) T cells to combat viral challenge, acts - directly or indirectly - to limit its further production.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis Decreases Human Macrophage IFN-γ Responsiveness through miR-132 and miR-26a

IFN-γ–activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis–infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

Mycobacterium tuberculosis decreases human macrophage IFN-γ responsiveness through miR-132 and miR-26a

IFN-γ-activated macrophages play an essential role in controlling intracellular pathogens; however, macrophages also serve as the cellular home for the intracellular pathogen Mycobacterium tuberculosis. Based on previous evidence that M. tuberculosis can modulate host microRNA (miRNA) expression, we examined the miRNA expression profile of M. tuberculosis-infected primary human macrophages. We identified 31 differentially expressed miRNAs in primary human macrophages during M. tuberculosis infection by NanoString and confirmed our findings by quantitative real-time RT-PCR. In addition, we determined a role for two miRNAs upregulated upon M. tuberculosis infection, miR-132 and miR-26a, as negative regulators of transcriptional coactivator p300, a component of the IFN-γ signaling cascade. Knockdown expression of miR-132 and miR-26a increased p300 protein levels and improved transcriptional, translational, and functional responses to IFN-γ in human macrophages. Collectively, these data validate p300 as a target of miR-132 and miR-26a, and demonstrate a mechanism by which M. tuberculosis can limit macrophage responses to IFN-γ by altering host miRNA expression.

[Human genetics of tuberculosis]

Tuberculosis (TB), caused by Mycobacterium tuberculosis, remains a major public health problem worldwide, resulting in 8.7 million new cases and 1.4 million deaths each year. One third of the world's population is exposed to M. tuberculosis and, after exposure, most, but not all, individuals become infected. Among infected subjects, only a minority (∼10%) will eventually develop clinical disease, which is typically either a primary, often extra-pulmonary, TB in children, or a reactivation, pulmonary TB in adults. Considerable genetic epidemiological evidence has accumulated to support a major role for human genetic factors in the development of TB. Numerous association studies with various candidate genes have been conducted in pulmonary TB, with very few consistent results. Recent genome-wide association studies revealed only a modest role for two inter-genic polymorphisms. However, a first major locus for pulmonary TB was mapped to chromosome 8q12-q13 in a Moroccan population after a genome-wide linkage screen. Using a similar strategy, two other major loci controlling TB infection were recently identified. While the precise identification of these major genes is ongoing, the other fascinating observation of these last years was the demonstration that TB can also reflect a Mendelian predisposition. Following the findings obtained in the syndrome of Mendelian susceptibility to mycobacterial diseases, several children with complete IL-12Rβ1 deficiency, were found to have severe TB as their sole phenotype. Overall, these recent findings provide the proof of concept that the human genetics of TB involves a continuous spectrum from Mendelian to complex predisposition with intermediate major gene involvement. The understanding of the molecular genetic basis of TB will have fundamental immunological and medical implications, in particular for the development of new vaccines and treatments.

IFN production ability and healthy ageing: mixed model analysis of a 24 year longitudinal study in Japan

OBJECTIVE

To track changes in interferon (IFN) production in healthy individuals to shed light on the effect these changes have on the course of healthy ageing.

DESIGN

Study is based on data that were collected over 24 years from a cohort of individuals whose IFN-α production was quantified as a part of their annual routine health check-up.

SETTING

All individuals in this study underwent regular health check-ups at Louis Pasteur Center for Medical Research.

PARTICIPANTS

295 healthy individuals (159 males and 136 females) without a history of cancer, autoimmune diseases and hepatitis C virus (HCV) whose IFN-α production was quantified more than five times within 24 years were selected. Finally, 29 males and 4 females whose IFN-α production was quantified more than 25 times were selected and their data were analysed using a mixed model.

MAIN OUTCOME MEASURES

HVJ stimulated IFN-α  production was quantified. Healthy individual's periodical log transformed IFN-α values (y) were plotted versus age (x) and fitted to linear (y=mx+n) and quadratic formula (y=ax(2)+bx+c) expressions to reveal changes in the IFN-α  production in these healthy individuals.

RESULTS

The linear expression showed that log (IFN-α) had a slight tendency to decline (3% over 10 years). However, the quadratic formula analysis showed the quadratic expression to be more positive than negative (a concave U-shaped pattern) which means that individuals' once declining IFN production recovered as they aged.

CONCLUSIONS

Although we observed a marginal decline in IFN-α  production, we also observed that IFN production recovered even in individuals in their mid50s to early 60s. These results combined with our previous cross-sectional studies of patients with various diseases suggest that in healthy individuals, the impairment of IFN production is triggered more by the onset of disease (notwithstanding the cause) rather than by ageing.

Suppression of the NF-κB pathway by diesel exhaust particles impairs human antimycobacterial immunity

Epidemiological studies suggest that chronic exposure to air pollution increases susceptibility to respiratory infections, including tuberculosis in humans. A possible link between particulate air pollutant exposure and antimycobacterial immunity has not been explored in human primary immune cells. We hypothesized that exposure to diesel exhaust particles (DEP), a major component of urban fine particulate matter, suppresses antimycobacterial human immune effector cell functions by modulating TLR-signaling pathways and NF-κB activation. We show that DEP and H37Ra, an avirulent laboratory strain of Mycobacterium tuberculosis, were both taken up by the same peripheral human blood monocytes. To examine the effects of DEP on M. tuberculosis-induced production of cytokines, PBMC were stimulated with DEP and M. tuberculosis or purified protein derivative. The production of M. tuberculosis and purified protein derivative-induced IFN-γ, TNF-α, IL-1β, and IL-6 was reduced in a DEP dose-dependent manner. In contrast, the production of anti-inflammatory IL-10 remained unchanged. Furthermore, DEP stimulation prior to M. tuberculosis infection altered the expression of TLR3, -4, -7, and -10 mRNAs and of a subset of M. tuberculosis-induced host genes including inhibition of expression of many NF-κB (e.g., CSF3, IFNG, IFNA, IFNB, IL1A, IL6, and NFKBIA) and IFN regulatory factor (e.g., IFNG, IFNA1, IFNB1, and CXCL10) pathway target genes. We propose that DEP downregulate M. tuberculosis-induced host gene expression via MyD88-dependent (IL6, IL1A, and PTGS2) as well as MyD88-independent (IFNA, IFNB) pathways. Prestimulation of PBMC with DEP suppressed the expression of proinflammatory mediators upon M. tuberculosis infection, inducing a hyporesponsive cellular state. Therefore, DEP alters crucial components of antimycobacterial host immune responses, providing a possible mechanism by which air pollutants alter antimicrobial immunity.

Virulence of Mycobacterium tuberculosis depends on lipoamide dehydrogenase, a member of three multienzyme complexes

Mycobacterium tuberculosis (Mtb) adapts to persist in a nutritionally limited macrophage compartment. Lipoamide dehydrogenase (Lpd), the third enzyme (E3) in Mtb's pyruvate dehydrogenase complex (PDH), also serves as E1 of peroxynitrite reductase/peroxidase (PNR/P), which helps Mtb resist host-reactive nitrogen intermediates. In contrast to Mtb lacking dihydrolipoamide acyltransferase (DlaT), the E2 of PDH and PNR/P, Lpd-deficient Mtb is severely attenuated in wild-type and immunodeficient mice. This suggests that Lpd has a function that DlaT does not share. When DlaT is absent, Mtb upregulates an Lpd-dependent branched-chain keto acid dehydrogenase (BCKADH) encoded by pdhA, pdhB, pdhC, and lpdC. Without Lpd, Mtb cannot metabolize branched-chain amino acids and potentially toxic branched-chain intermediates accumulate. Mtb deficient in both DlaT and PdhC phenocopies Lpd-deficient Mtb. Thus, Mtb critically requires BCKADH along with PDH and PNR/P for pathogenesis. These findings position Lpd as a potential target for anti-infectives against Mtb.

Genomic structure and characterization of mRNA expression pattern of porcine interferon gamma receptor 1 gene

Interferon gamma receptor (IFNGR) plays an important role in the biological effects of IFN-γ. In this study, porcine IFNGR1 cDNA was cloned and two transcripts both having a coding region of 1413 bp were identified. Porcine IFNGR1 cDNA shares 62.95%, 63.73%, 72.90% and 81.10% identity in nucleotide sequence; and 45.64%, 46.69%, 58.04% and 72.55% homology in amino acid sequence to those of rat, mouse, human and cattle, respectively. The porcine IFNGR1 genomic structure consists of seven exons and six introns and is located on porcine chromosome 1. The mRNA expression of porcine IFNGR1 gene is detected in all tissues examined, with strong expression in spleen and liver tissues and weak expression in cerebrum, cerebellum and uterus tissues, respectively. A different developmental pattern in IFNGR1 mRNA expression between Laiwu and Duroc breeds was revealed by real-time quantitative RT-PCR: in Duroc pigs, a significantly higher expression was found in the tissues of heart (P<0.05), liver (P<0.01), kidney (P<0.01) and skeletal muscle (P<0.05) of adult pigs compared to piglets. In porcine reproductive and respiratory syndrome virus (PRRSV)-infected Dapulian pigs, compared to the uninfected ones, the expression level of IFNGR1 mRNA in spleen was significantly up-regulated (P<0.05), whereas its expression in the lymph node was significantly down-regulated (P<0.05); in PRRSV-infected Duroc × Yorkshire × Landrace commercial pigs, however, the differences both in spleen and lymph node tissues were not significant.

Fighting mycobacterial infections by antibiotics, phytochemicals and vaccines

Buruli ulcer is a neglected disease caused by Mycobacterium ulcerans and represents the world's third most common mycobacterial infection. It produces the polyketide toxins, mycolactones A, B, C and D, which induce apoptosis and necrosis. Clinical symptoms are subcutaneous nodules, papules, plaques and ulcerating oedemae, which can enlarge and destroy nerves and blood vessels and even invade bones by lymphatic or haematogenous spread (osteomyelitis). Patients usually do not suffer from pain or systematic inflammation. Surgery is the treatment of choice, although recurrence is common and wide surgical excisions including healthy tissues result in significant morbidity. Antibiotic therapy with rifamycins, aminoglycosides, macrolides and quinolones also improves cure rates. Still less exploited treatment options are phytochemicals from medicinal plants used in affected countries. Vaccination against Buruli ulcer is still in its infancy.

Molecular mechanisms of IFN-gamma to up-regulate MHC class I antigen processing and presentation

IFN-gamma up-regulates MHC class I expression and antigen processing and presentation on cells, since IFN-gamma can induce multiple gene expressions that are related to MHC class I antigen processing and presentation. MHC class I antigen presentation-associated gene expression is initiated by IRF-1. IRF-1 expression is initiated by phosphorylated STAT1. IFN-gamma binds to IFN receptors, and then activates JAK1/JAK2/STAT1 signal transduction via phosphorylation of JAK and STAT1 in cells. IFN-gamma up-regulates MHC class I antigen presentation via activation of JAK/STAT1 signal transduction pathway. Mechanisms of IFN-gamma to enhance MHC class I antigen processing and presentation were summarized in this literature review.

Mycobacterial subversion of chemotherapeutic reagents and host defense tactics: challenges in tuberculosis drug development

Recent worldwide emergence of multidrug-resistant and extensively drug-resistant tuberculosis is threatening to destabilize tuberculosis control programs and urging global attention to the development of alternative tuberculosis therapies. Major roadblocks limiting the development and effectiveness of new drugs to combat tuberculosis are the profound innate resistance of Mycobacterium tuberculosis to host defense mechanisms as well as its intrinsic tolerance to chemotherapeutic reagents. The triangle of interactions among the pathogen, the host responses, and the drugs used to cure the disease are critical for the outcome of tuberculosis. We must better understand this three-way interaction in order to develop drugs that are able to kill the bacillus in the most effective way and minimize the emergence of drug resistance. Here we review our recent understanding of the molecular basis underlying intrinsic antibiotic resistance and survival tactics of M. tuberculosis. This knowledge may help to reveal current targets for the development of novel antituberculosis drugs.

Compartmentalized bronchoalveolar IFN-gamma and IL-12 response in human pulmonary tuberculosis

Human tuberculosis (TB) principally involves the lungs, where local immunity impacts on the load of Mycobacterium tuberculosis (M.tb). Because concomitants of local Th1 immunity are still under-explored in humans, we characterized immune responses in bronchoalveolar cells (BACs) and systemically in peripheral blood mononuclear cells (PBMCs) in persons with active pulmonary TB and in healthy community controls. PPD- and live M.tb-induced IFN-gamma-production were observed in CD4(+), CD8(+), gammadeltaTCR(+), and CD56(+) alveolar T cell subpopulations and NK cells (CD3(-)CD56(+)). IFN-gamma-producing CD4(+) T cells (mostly CD45RO(+)) were more abundant (p<0.05). M.tb-induced IL-12p70, but interestingly also IL-4, was increased (p<0.05) in BACs from TB patients. Constitutive expression of IL-12Rbeta1 and IL-12Rbeta2 mRNA in BACs and PBMCs and IFN-gammaR1 in BACs was similar in both study groups. Data were normalized to account for differences in proportions of alveolar T cells and macrophages in the study groups. IFN-gamma-production and its induction by IL-12R engagement occur virtually unimpaired in the bronchoalveolar spaces of patients with pulmonary TB. The reasons for the apparent failure to control M. tuberculosis growth during active pulmonary TB disease is unknown but could be the expression of locally acting immunosuppressive mechanisms that subvert the antimycobacterial effects of IFN-gamma.

Genetically determined susceptibility to mycobacterial infection

Individuals with impaired cell mediated immunity exhibit increased susceptibility to infections caused by poorly pathogenic mycobacteria (non-tuberculous mycobacteria and BCG), as well as salmonella species. However, these infections may also occur in a disseminated, fatal form, sometimes with a familial distribution, in the absence of any recognised primary or secondary immunodeficiency. Genetic analysis of affected families has defined mutations in seven different genes participating in the interleukin 12 (IL12) dependent, high output interferon gamma (IFNgamma) pathway. The first category of defect is mutations in the IFNgammaR1 or R2 genes, resulting in defective expression or function of the IFNgamma receptor. The second category of mutations abrogates the cell surface expression IL12Rbeta1gene, resulting in the inability to respond to IL12. The third category of defect is the inability to produce IL12, due to deletion within the gene coding for the inducible chain of IL12 (IL12-p40). Patients with X-linked recessive mutations of the gene encoding the NFkappaB essential modulator may also develop mycobacterial infections, although they usually have a more complex phenotype and are susceptible to a broad spectrum of pathogens. Mutations of the gene encoding the signal transducing molecule STAT1, which impairs the ability to respond to IFNgamma, and mutations of the gene encoding TYK2 (which is associated with a failure to respond to IL12), are both rare genetic defects predisposing to mycobacterial infections. This review summarises the clinical spectrum seen in this group of patients and indicates a strategy for the identification of putative genetic defects in the type-1 cytokine pathway.

Reduced TH-1 cytokine release in an adult patient with chronic relapsing Mycobacterium malmoense infection

An unusual course of infection with Mycobacterium malmoense is described in a patient receiving chronic but mild immunosuppressive therapy for rheumatoid arthritis. Symptoms mimicking Crohn's disease deteriorated under intensified immunosuppression and surgery. Judging from the patient's course under treatment specific for M. malmoense, the gastrointestinal symptoms were rather manifestations of a chronic relapsing mycobacterial infection. Detailed immunological investigation of the patient revealed a severely impaired TH-1 cytokine response as the immunological background for this uncommon course.

Human primary immunodeficiencies of type I interferons

Type I interferons (IFN-alpha/beta and related molecules) are essential for protective immunity to experimental infection by numerous viruses in the mouse model. In recent years, human primary immunodeficiencies affecting either the production of (UNC-93B deficiency) or the response to (STAT1 and TYK2 deficiencies) these IFNs have been reported. Affected patients are highly susceptible to certain viruses. Patients with STAT1 or TYK2 deficiency are susceptible to multiple viruses, including herpes simplex virus-1 (HSV-1), whereas UNC-93B-deficient patients present isolated HSV-1 encephalitis. However, these immunological defects are not limited to type I IFN-mediated immunity. Impaired type II IFN (IFN-gamma)-mediated immunity plays no more than a minor role in the pathogenesis of viral diseases in these patients, but the contribution of impaired type III IFN (IFN-lambda)-mediated immunity remains to be determined. These novel inherited disorders strongly suggest that type I IFN-mediated immunity is essential for protection against natural infections caused by several viruses in humans.

The Impact on Coronary Artery Disease of Common Polymorphisms Known to Modulate Responses to Pathogens

There are two distinct models to explain how genetic variants contributing to cardiovascular disease may have arisen. Firstly, variants may result from random, initially neutral, mutations whose effects are largely revealed in post-reproductive individuals in industrialized societies. Alternatively, the introduced variants may confer an adaptive advantage in certain circumstances. Resistance to pathogens is one of the strongest selection pressures on human proteins. To determine whether this evolutionary pressure has made a large contribution to heart disease we tested whether seventeen polymorphisms in fourteen innate-immunity genes, with documented evidence of modulating response to pathogens, had an impact on heart disease. Genotyping was performed in 1,598 CAD subjects (ACS or stable angina) and 332 controls. The TLR4 399Ile allele had the greatest impact on ACS risk (uncorrected p = 0.006); however there was no evidence overall that the resistance alleles cumulatively influenced the risk of ACS compared to controls or stable angina patients (p = 0.12, and p = 0.40, respectively). We did note a significant interaction between age at onset of disease and combined resistance allele carriership when the ACS and non-thrombotic, stable angina groups were compared (p = 0.04, 16 d.f.). This suggests that innate immunity factors could have a greater impact on thrombus formation among younger CAD patients.

Expression of T-bet by CD4 T cells is essential for resistance to Salmonella infection

Despite the recognized role of the T-bet transcription factor in the differentiation of Th1 cells, T-bet-deficient mice can develop small numbers of IFN-gamma-producing CD4 T cells. Although these are not sufficient to allow normal handling of some pathogens, T-bet-deficient mice do resolve infection with the intracellular pathogen Listeria monocytogenes. In contrast, we report that expression of T-bet is required for resistance to Salmonella infection. T-bet-deficient mice succumbed to infection with attenuated Salmonella and did not generate IFN-gamma-producing CD4 T cells or isotype-switched Salmonella-specific Ab responses. Spleen cells from Salmonella-infected T-bet-deficient mice secreted increased levels of IL-10, but not IL-4, upon in vitro restimulation. A Salmonella-specific TCR transgenic adoptive transfer system was used to further define the involvement of T-bet expression in the development of Salmonella-specific Th1 cells. Wild-type Salmonella-specific CD4 T cells activated in T-bet-deficient recipient mice displayed no defect in clonal expansion, contraction, or IFN-gamma production. In contrast, T-bet-deficient, Salmonella-specific CD4 T cells activated in wild-type recipient mice produced less IFN-gamma and more IL-2 upon in vivo restimulation. Therefore, expression of T-bet by CD4 T cells is required for the development of Salmonella-specific Th1 cells, regulation of IL-10 production, and resistance to Salmonella infection.

Mycobacterium tuberculosis growth control by lung macrophages and CD8 cells from patient contacts

RATIONALE

Healthy household contacts (HHCs) of patients with active pulmonary tuberculosis are exposed aerogenically to Mycobacterium tuberculosis (Mtb), thus permitting the study of protective local immunity.

OBJECTIVES

To assess alveolar macrophage (AM) and autologous blood CD4 and CD8 T-cell-mediated Mtb growth control in HHCs and healthy, unexposed community control subjects (CCs).

METHODS

AMs were infected with Mtb strains H(37)Ra and H(37)Rv at multiplicities of infection 0.1 and 1. Mtb colony-forming units were evaluated on Days 1, 4, and 7.

MAIN RESULTS

CD8 T cells from HHCs in 1:1 cocultures with AMs significantly (p < 0.05) increased Mtb growth control by AMs. In CCs, no detectable contribution of CD8 T cells to Mtb growth control was observed. CD4 T cells did not increase Mtb growth control in HHCs or in CCs. IFN-gamma, nitric oxide, and tumor necrosis factor were determined as potential mediators of Mtb growth control in AMs and AM/CD8 and AM/CD4 cocultures. IFN-gamma production in AM/CD4 was twofold higher than that in AM/CD8 cocultures in both HHCs and CCs (p < 0.05). Nitric oxide production from AMs of HHCs increased on Days 4 and 7 and was undetectable in AMs from CCs. IFN-gamma and nitric acid concentrations and Mtb growth control were not correlated. Tumor necrosis factor levels were significantly increased in AM/CD8 cocultures from HHCs compared with AM/CD8 cocultures from CCs (p < 0.05).

CONCLUSION

Aerogenic exposure to Mtb in HHCs leads to expansion of Mtb-specific effector CD8 T cells that limit Mtb growth in autologous AMs.

Congenital immunodeficiencies and sepsis

OBJECTIVE

Because a hallmark of congenital immunodeficiency disorders is susceptibility to recurrent, unusual and/or severe infections, an effort was undertaken to identify a subset of these patients with an increased risk for sepsis.

DESIGN

Literature review.

RESULTS

Twenty congenital immunodeficiency disorders were identified with increased sepsis susceptibility.

CONCLUSION

Distinguishing patients with congenital immunodeficiencies from others with sepsis has important implications for the future well-being of the immunodeficient patient because many of the diseases are modified favorably by appropriate treatment. In addition, better understanding of sepsis in the setting of congenital immunodeficiency has numerous implications for both immunodeficiency and sepsis research. As a group, these disorders define components of the human immune system that are essential for defense against severe infection and demonstrate immunologic themes underlying sepsis susceptibility.

The role of IL-12, IL-23 and IFN-gamma in immunity to viruses

IL-12, IL-23 and IFN-γ form a loop and have been thought to play a crucial role against infectious viruses, which are the prototype of “intracellular” pathogens. In the last 10 years, the generation of knock-out (KO) mice for genes that control IL-12/IL-23-dependent IFN-γ-dependent mediated immunity (STAT1, IFN-γR1, IFNγR2, IL-12p40 and IL-12Rβ1) and the identification of patients with spontaneous germline mutations in these genes has led to a re-examination of the role of these cytokines in anti-viral immunity. We here review viral infections in mice and humans with genetic defects in the IL-12/IL-23-IFN-γ axis. A comparison of the phenotypes observed in KO mice and deficient patients suggests that the human IL-12/IL-23-IFN-γ axis plays a redundant role in immunity to most viruses, whereas its mouse counterparts play a more important role against several viruses.

Interferon-gamma: an overview of signals, mechanisms and functions

Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.

Human deficiencies in type-1 cytokine receptors reveal the essential role of type-1 cytokines in immunity to intracellular bacteria

Human genetic factors play an important role in determining the outcome of infections caused by intracellular pathogens, including mycobacteria and salmonellae (reviewed in 1). The genetic elements involved and the mechanisms by which these control disease-susceptibility versus resistance, however, remain incompletely characterized. Recent studies on patients with idiopathic, severe infections due to poorly pathogenic mycobacteria and salmonellae have revealed that many of these patients are unable to produce or respond to IFN-gamma. This inability results from causative, deleterious genetic mutations in either one of five different genes in the type-1 cytokine cascade, encoding IL-12p40, IL-12Rbeta1, IFN-gammaR1, IFN-gammaR2 or Stat-1. The mutational events can lead to complete or partial deficiency, and are mostly autosomal recessive but can be dominant negative as well. The immunological, clinical and histopathological phenotypes resulting from the ten groups of genetic type-1 cytokine (receptor) deficiency distinguished thus far differ significantly. These findings are summarized, discussed and placed in a broader context in relation to protective immune mechanisms and disease susceptibility.

Sensitization of IFN-gamma Jak-STAT signaling during macrophage activation

A general paradigm in signal transduction is ligand-induced feedback inhibition and the desensitization of signaling. We found that subthreshold concentrations of interferon-gamma (IFN-gamma), which did not activate macrophages, increased their sensitivity to subsequent IFN-gamma stimulation; this resulted in increased signal transducer and activator of transcription 1 (STAT1) activation and increased IFN-gamma#150;dependent gene activation. Sensitization of IFN-gamma signaling was mediated by the induction of STAT1 expression by low doses of IFN-gamma that did not effectively induce feedback inhibition. IFN-gamma signaling was sensitized in vivo after IFN-gamma injection, and STAT1 expression was increased after injection of lipopolysaccharide and in rheumatoid arthritis synovial cells. These results identify a mechanism that sensitizes macrophages to low concentrations of IFN-gamma and regulates IFN-gamma responses in acute and chronic inflammation.

Genetic dissection of immunity to mycobacteria: the human model

Humans are exposed to a variety of environmental mycobacteria (EM), and most children are inoculated with live Bacille Calmette-Guérin (BCG) vaccine. In addition, most of the world's population is occasionally exposed to human-borne mycobacterial species, which are less abundant but more virulent. Although rarely pathogenic, mildly virulent mycobacteria, including BCG and most EM, may cause a variety of clinical diseases. Mycobacterium tuberculosis, M. leprae, and EM M. ulcerans are more virulent, causing tuberculosis, leprosy, and Buruli ulcer, respectively. Remarkably, only a minority of individuals develop clinical disease, even if infected with virulent mycobacteria. The interindividual variability of clinical outcome is thought to result in part from variability in the human genes that control host defense. In this well-defined microbiological and clinical context, the principles of mouse immunology and the methods of human genetics can be combined to facilitate the genetic dissection of immunity to mycobacteria. The natural infections are unique to the human model, not being found in any of the animal models of experimental infection. We review current genetic knowledge concerning the simple and complex inheritance of predisposition to mycobacterial diseases in humans. Rare patients with Mendelian disorders have been found to be vulnerable to BCG, a few EM, and M. tuberculosis. Most cases of presumed Mendelian susceptibility to these and other mycobacterial species remain unexplained. In the general population leprosy and tuberculosis have been shown to be associated with certain human genetic polymorphisms and linked to certain chromosomal regions. The causal vulnerability genes themselves have yet to be identified and their pathogenic alleles immunologically validated. The studies carried out to date have been fruitful, initiating the genetic dissection of protective immunity against a variety of mycobacterial species in natural conditions of infection. The human model has potential uses beyond the study of mycobacterial infections and may well become a model of choice for the investigation of immunity to infectious agents.

Distribution of IFN-gamma, IL-4 and TNF-alpha protein and CD8 T cells producing IL-12p40 mRNA in human lung tuberculous granulomas

In order to examine the immune response at the site of pathology in tuberculosis, we analysed cytokines present in lung granulomas, their associations with each other and with caseous necrosis as well as the phenotype of the cellular infiltrate. Paraffin-embedded tissue from the lungs of seven patients with pulmonary tuberculosis was analysed by immunohistochemistry and in situ hybridization to detect interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4) proteins and IL-12p40 mRNA. All seven patients had granulomas staining positive for IFN-gamma, TNF-alpha and IL-12p40, but only four stained positive for IL-4. Cells with the morphology of lymphocytes, macrophages and giant cells expressed TNF-alpha, IFN-gamma and IL-4 protein. Furthermore, CD68-positive myeloid cells expressed IL-12p40 mRNA, as expected, but a subset of CD3-positive lymphocytes also expressed this mRNA. These lymphocytes producing IL-12p40 also stained positive for CD8 but not CD4. A total of 141 granulomas were scored for the presence or absence of cytokine or necrosis and two major associations were identified. The first association was between IFN-gamma and IL-12, with 76% of granulomas staining positive for both cytokines. Unexpectedly, those granulomas positive for IL-4 were always positive for IFN-gamma. The second association was between TNF-alpha and caseous necrosis, where all necrotic granulomas were TNF-alpha positive. This association was modulated by IL-4. Therefore, heterogeneity of cellular infiltrate and cytokine expression is observed between adjacent granulomas in the same patient.

Heterogeneity in the granulomatous response to mycobacterial infection in patients with defined genetic mutations in the interleukin 12-dependent interferon-gamma production pathway

Patients with genetic lesions in the Type-1 cytokine/cytokine receptor pathway exhibit a selective susceptibility to severe infections with poorly pathogenic mycobacteria and non-typhi salmonella spp. These experiments of nature demonstrate that IL-12-dependent IFNgamma production is critical for granuloma formation and therefore host immunity against such pathogens. The essential role of granuloma formation for protective immunity to these organisms is emphasized by the differing granuloma forming capabilities and resultant clinical sequelae observed in these patients which seems to reflect their ability to produce or respond to IFNgamma (Fig. 9). At one pole of this spectrum, represented by the complete IFNgammaR1/2 deficient patients, there is a complete absence of mature granuloma formation, whereas with the less severe mutations (i.e. partial IFNgammaR1/2, complete IL-12p40 and complete IL-12Rbeta1 deficiency), granuloma formation is very heterogenous with wide variations in composition being observed. This suggests that in the latter individuals, who produce partial but suboptimal IFNgamma responses, other influences, including pathogen virulence and host genotype may also affect the type and scale of the cellular response elicited.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

Interferon-gamma and interleukin-12 pathway defects and human disease

A genetic component to human mycobacterial disease susceptibility has long been postulated. Over the past five years, mutations in the interferon-gamma (IFNgamma) receptor, IL-12 receptor beta1 (IL-12Rbeta1), and IL-12 p40 genes have been recognized. These mutations are associated with heightened susceptibility to disease caused by intracellular pathogens including nontuberculous mycobacteria, vaccine-associated bacille Calmette Guerin (BCG), Salmonella species, and some viruses. We describe the genotype-phenotype correlations in IFNgamma receptor, IL-12Rbeta1, and IL-12 p40 deficiency, and discuss how study of these diseases has enhanced knowledge of human host defense against mycobacteria and other intracellular pathogens.

Human deficiencies in type 1 cytokine receptors reveal the essential role of type 1 cytokines in immunity to intracellular bacteria

Studies on patients with idiopathic, severe infections due to poorly pathogenic mycobacteria and Salmonella have revealed that many of these patients are unable to produce or respond to interferon-gamma (IFN-gamma). This inability results from causative, deleterious genetic mutations in either one of four different genes in the type 1 cytokine cascade, encoding interleukin-12Rbeta1 (IL-12Rbeta1), IL-12p40, IFN-gammaR1 or IFN-gammaR2. The immunological phenotypes resulting from the seven groups of complete or partial deficiencies in type 1 cytokine (receptor) genes that have been distinguished thus far will be summarized and discussed, and placed in a broader context in relation to disease susceptibility.

Diagnosis of defects in the type 1 cytokine pathway

Patients with inherited defects in the interleukin-12 (IL-12)-dependent, 'high-output' interferon-gamma (IFN-gamma) pathway exhibit selective susceptibility to poorly pathogenic mycobacterial and salmonella infections. This review summarises the extended clinical spectrum seen in this group of patients and indicates a strategy for the identification of putative defects in the type 1 cytokine pathway.

In a novel form of IFN-gamma receptor 1 deficiency, cell surface receptors fail to bind IFN-gamma

Complete IFN-gamma receptor ligand-binding chain (IFNgammaR1) deficiency is a life-threatening autosomal recessive immune disorder. Affected children invariably die of mycobacterial infection, unless bone marrow transplantation is undertaken. Pathogenic IFNGR1 mutations identified to date include nonsense and splice mutations and frameshift deletions and insertions. All result in a premature stop codon upstream from the segment encoding the transmembrane domain, precluding cell surface expression of the receptors. We report herein two sporadic and two familial cases of a novel form of complete IFNgammaR1 deficiency in which normal numbers of receptors are detected at the cell surface. Two in-frame deletions and two missense IFNGR1 mutations were identified in the segment encoding the extracellular ligand-binding domain of the receptor. Eight independent IFNgammaR1-specific mAb's, including seven blocking antibodies, gave recognition patterns that differed between patients, suggesting that different epitopes were altered by the mutations. No specific binding of (125)I-IFN-gamma to cells was observed in any patient, however, and the cells failed to respond to IFN-gamma. The mutations therefore cause complete IFNgammaR1 deficiency by disrupting the IFN-gamma-binding site without affecting surface expression. The detection of surface IFNgammaR1 molecules by specific antibodies, including blocking antibodies, does not exclude a diagnosis of complete IFNgammaR1 deficiency.

Circulating, Mycobacterium tuberculosis-specific lymphocytes from PPD skin test-negative patients with tuberculosis do not secrete interferon-gamma (IFN-gamma) and lack the cutaneous lymphocyte antigen skin-selective homing receptor

Individuals with a negative intradermal reaction to tuberculin PPD have long been described in the Mycobacterium tuberculosis exposed, immune-competent population. Here, we studied PPD-specific blood T lymphocytes from these subjects for phenotypic markers relevant to skin migration, including the expression of the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen (CLA). Out of 82 patients with active tuberculosis we identified four subjects who were repeatedly PPD skin test-negative. CD4 T lymphocytes specific to mycobacterial antigens were derived from these individuals, which (i) proliferated in vitro to M. tuberculosis antigens comparably to those from PPD+ patients; (ii) secreted comparable amounts of IL-2 but lower amounts of IFN-gamma; (iii) were confined within the CLA-negative T cell subset. We conclude that the negative tuberculin reaction in a small subset of patients exposed to mycobacteria is associated with impaired production of IFN-gamma by circulating PPD-specific T cells that are lacking CLA expression. On this basis in vitro proliferation to PPD can discriminate bona fide non-responders from infected patients with a deficit in the margination of M. tuberculosis-specific T lymphocytes.

Viral infections in interferon-gamma receptor deficiency

Interferon-gamma receptor deficiency is a recently described immunodeficiency that is associated with onset of severe mycobacterial infections in childhood. We describe the occurrence of symptomatic and often severe viral infections in 4 patients with interferon-gamma receptor deficiency and mycobacterial disease. The viral pathogens included herpes viruses, parainfluenza virus type 3, and respiratory syncytial virus. We conclude that patients with interferon-gamma receptor deficiency and mycobacterial disease have increased susceptibility to some viral pathogens.