A human IFNGR1 small deletion hotspot associated with dominant susceptibility to mycobacterial infection.

The immunogenetic basis of severe infections caused by bacille Calmette-Guérin vaccine and environmental mycobacteria in humans remains largely unknown. We describe 18 patients from several generations of 12 unrelated families who were heterozygous for 1 to 5 overlapping IFNGR1 frameshift small deletions and a wild-type IFNGR1 allele. There were 12 independent mutation events at a single mutation site, defining a small deletion hotspot. Neighbouring sequence analysis favours a small deletion model of slipped mispairing events during replication. The mutant alleles encode cell-surface IFNgamma receptors that lack the intra-cytoplasmic domain, which, through a combination of impaired recycling, abrogated signalling and normal binding to IFNgamma exert a dominant-negative effect. We thus report a hotspot for human IFNGR1 small deletions that confer dominant susceptibility to infections caused by poorly virulent mycobacteria.

Impairment of mycobacterial immunity in human interleukin-12 receptor deficiency.

In humans, interferon gamma (IFN-gamma) receptor deficiency leads to a predisposition to mycobacterial infections and impairs the formation of mature granulomas. Interleukin-12 (IL-12) receptor deficiency was found in otherwise healthy individuals with mycobacterial infections. Mature granulomas were seen, surrounded by T cells and centered with epithelioid and multinucleated giant cells, yet reduced IFN-gamma concentrations were found to be secreted by activated natural killer and T cells. Thus, IL-12-dependent IFN-gamma secretion in humans seems essential in the control of mycobacterial infections, despite the formation of mature granulomas due to IL-12-independent IFN-gamma secretion.

Partial interferon-gamma receptor 1 deficiency in a child with tuberculoid bacillus Calmette-Guérin infection and a sibling with clinical tuberculosis.

Complete interferon-gamma receptor 1 (IFNgammaR1) deficiency has been identified previously as a cause of fatal bacillus Calmette-Guérin (BCG) infection with lepromatoid granulomas, and of disseminated nontuberculous mycobacterial (NTM) infection in children who had not been inoculated with BCG. We report here a kindred with partial IFNgammaR1 deficiency: one child afflicted by disseminated BCG infection with tuberculoid granulomas, and a sibling, who had not been inoculated previously with BCG, with clinical tuberculosis. Both responded to antimicrobials and are currently well without prophylactic therapy. Impaired response to IFN-gamma was documented in B cells by signal transducer and activator of transcription 1 nuclear translocation, in fibroblasts by cell surface HLA class II induction, and in monocytes by cell surface CD64 induction and TNF-alpha secretion. Whereas cells from healthy children responded to even low IFN-gamma concentrations (10 IU/ml), and cells from a child with complete IFNgammaR1 deficiency did not respond to even high IFN-gamma concentrations (10,000 IU/ml), cells from the two siblings did not respond to low or intermediate concentrations, yet responded to high IFN-gamma concentrations. A homozygous missense IFNgR1 mutation was identified, and its pathogenic role was ascertained by molecular complementation. Thus, whereas complete IFNgammaR1 deficiency in previously identified kindreds caused fatal lepromatoid BCG infection and disseminated NTM infection, partial IFNgammaR1 deficiency in this kindred caused curable tuberculoid BCG infection and clinical tuberculosis.

Inherited interleukin 12 deficiency in a child with bacille Calmette-Guérin and Salmonella enteritidis disseminated infection.

Interferon-gamma receptor ligand-binding chain (IFN-gammaR1) or signaling chain (IFN-gammaR2) deficiency, like interleukin 12 receptor beta1 chain (IL-12Rbeta1) deficiency, predispose to severe infections due to poorly virulent mycobacteria and salmonella. A child with bacille Calmette-Guérin and Salmonella enteritidis infection was investigated. Mutations in the genes for IFN-gammaR1, IFN-gammaR2, IL-12Rbeta1, and other molecules implicated in IL-12- or IFN-gamma-mediated immunity were sought. A large homozygous deletion within the IL-12 p40 subunit gene was found, precluding expression of functional IL-12 p70 cytokine by activated dendritic cells and phagocytes. As a result, IFN-gamma production by lymphocytes was markedly impaired. This is the first discovered human disease resulting from a cytokine gene defect. It suggests that IL-12 is essential to and appears specific for protective immunity to intracellular bacteria such as mycobacteria and salmonella.

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.

Mendelian susceptibility to mycobacterial infection in man.

Selective susceptibility to poorly pathogenic mycobacteria, such as bacille Calmette-Guérin vaccine and environmental non-tuberculous mycobacteria, has long been suspected to be a mendelian disorder but its molecular basis has remained elusive. Recently, recessive mutations in the interferon-gamma-receptor receptor ligand-binding chain, interferon-gamma-receptor signalling chain, IL-12 p40 subunit and IL-12-receptor beta 1 chain genes have been identified in a number of patients with disseminated mycobacterial infection. Although genetically distinct, these conditions are immunologically related and highlight the essential role of interferon-gamma-mediated immunity in the control of mycobacteria in man.

IL-12 and IFN-gamma in host defense against mycobacteria and salmonella in mice and men.

The development of gene-knockout mice and the identification of gene-deficient humans have improved our understanding of the role of IL-12 and IFN-gamma in host defense. Comparison of experimental and natural infections has shown that animals and humans genetically deficient in immunity mediated by IL-12 or IFN-gamma are highly susceptible to mycobacteria and salmonella. Impaired secretion of, or response to, IFN-gamma is the common pathogenic mechanism that accounts for impaired granuloma formation and uncontrolled growth of bacteria within macrophages. The axis formed between IL-12 and IFN-gamma is essential for protective immunity against mycobacteria and salmonella in mice and men.

LPS-induced immune response in Drosophila.

The study of the regulation of the inducible synthesis of antimicrobial peptides in Drosophila melanogaster has established this insect as a powerful model in which to study innate immunity. In particular, the molecular characterization of the regulatory pathway controlling the antifungal peptide drosomycin has revealed the importance of Toll receptors in innate immunity. We report here that injection of LPS into flies induces an immune response, suggesting that LPS receptors are used in Drosophila to detect Gram-negative bacteria infection. We have identified in the recently sequenced genome of Drosophila eight genes coding for Toll-like receptors in addition to Toll, which may function as LPS receptors. However, overexpression of a selection of these genes in tissue-culture cells does not result in up-regulation of the antibacterial peptide genes. These results are discussed in light of the recent data from genetic screens aimed at identifying the genes controlling the antibacterial response in Drosophila.

Infections in IFNGR-1-deficient children.

Human interferon-gamma receptor 1 (IFNGR-1) deficiency is a newly identified autosomal recessive inherited immune disorder. Children with IFNGR-1 deficiency exhibit a severe, profound and selective susceptibility to weakly virulent mycobacteria, such as bacillus Calmette-Guerin (BCG) vaccine or environmental nontuberculous mycobacteria (NTM). This review compares the infections found in IFNGR-1-deficient children to those in IFN-gamma-deficient or IFNGR-1-deficient mice.

Idiopathic disseminated bacillus Calmette-Guérin infection: a French national retrospective study.

OBJECTIVE: Disseminated bacillus Calmette-Guérin (BCG) infection after inoculation of live vaccine is considered to result from impaired immunity of the child. However, in half of the cases, regarded as idiopathic, no well-defined immunodeficiency condition can account for the infection. The objective of the present study is to report the prevalence, clinical features, associated infections, and outcomes of children with idiopathic disseminated BCG infection. DESIGN: National retrospective survey during the period from 1974 through 1994 in France. SETTING: All neonatology and pediatrics units in primary care and referral centers throughout France. PATIENTS: Data were collected from 595 (82%) of 721 units, 377 (93%) of 407 centers, and 320 (93%) of 345 cities. Selection criteria included BCG infection, dissemination to at least two areas beyond the inoculation site, and no well-defined immunodeficiency condition. Sixteen children (8 girls and 8 boys), born to families unrelated to each other but often consanguinous (5 of 16) or abroad (5 of 16). RESULTS: The minimal prevalence rate was estimated at 0.59 cases per 1 million vaccinated children born in France. Clinical features included fever and cachexia, disseminated BCG infection to lymph nodes (15 of 16), skin (13 of 16), soft tissues (11 of 16), lungs (11 of 16), spleen (11 of 16), liver (11 of 16), and bones (9 of 16). Eight children had associated or subsequent severe opportunistic infection (50%), with either nontyphi Salmonella enterica serotypes (7 of 16) or Mycobacterium abscessus (1 of 16). The outcome was poor: 8 children (50%) died; the cause of death was BCG infection for most children (7 of 8); 8 survived until the last follow-up (50%). CONCLUSIONS: Idiopathic disseminated BCG infection is a rare but severe complication of BCG vaccination. The infection probably results from an as yet unknown genetically determined immunodeficiency condition that affects the killing of intracellular bacteria such as BCG and Salmonella.

Interferon-gamma receptor deficiency: relationship between genotype, environment, and phenotype (Review).

Interferon-gamma receptor ligand binding chain (IFNgammaR1) deficiency is an autosomal recessive inherited immune disorder. Mutations in the IFNgR1 gene are associated with severe infections due to mycobacteria. However, several aspects of the phenotype of IFNgammaR1-deficient children have recently been found to vary from case to case. This review thus discusses the respective roles of the genotype and of the environment in determining phenotypic variations among affected children.

[Primary immunodeficiency secondary to ZAP-70 deficiency]. / Imunodeficiência primária por défice de ZAP-70.

The authors present the case of a child with recurrent infections since the age of 4 months, including bilateral pneumonia by Pneumocystis carinii and protracted varicella. Serum immunoglobulin values (when 10 months old), and B cell values were normal. There was persistent lymphocytic leucocytosis, near absence of CD8+ cells, and an increased CD4/CD8 ratio. The percentage of activated T cells and the expression of HLA class I were normal. Proliferation, activation and IL-2 synthesis studies in T cells showed a TCR/CD3-associated signal transduction deficit. ZAP-70 cDNA sequencing showed a mutation, and no ZAP-70 protein was detected in T cells. ZAP-70 deficiency is associated with a rare immune deficiency with absence of CD8+ T cells as well as a functional deficiency in T cells. Seven months after bone marrow transplantation the child is clinically well and immunologically recovered.

Toll-related receptors and the control of antimicrobial peptide expression in Drosophila.

Insects defend themselves against infectious microorganisms by synthesizing potent antimicrobial peptides. Drosophila has appeared in recent years as a favorable model to study this innate host defense. A genetic analysis of the regulation of the antifungal peptide drosomycin has demonstrated a key role for the transmembrane receptor Toll, which prompted the search for mammalian homologs. Two of these, Toll-like receptor (TLR)2 and TLR4, recently were shown to play a critical role in innate immunity against bacteria. Here we describe six additional Toll-related genes (Toll-3 to Toll-8) in Drosophila in addition to 18-wheeler. Two of these genes, Toll-3 and Toll-4, are expressed at a low level. Toll-6, -7, and -8, on the other hand, are expressed at high levels during embryogenesis and molting, suggesting that, like Toll and 18w, they perform developmental functions. Finally, Toll-5 is expressed only in larvae and adults. By using chimeric constructs, we have tested the capacity of the signaling Toll/IL-1R homology domains of these receptors to activate antimicrobial peptide promoters and found that only Toll and Toll-5 can activate the drosomycin promoter in transfected cells, thus demonstrating specificity at the level of the Toll/IL-1R homology domain. In contrast, none of these constructs activated antibacterial peptide promoters, suggesting that Toll-related receptors are not involved in the regulation of antibacterial peptide expression. This result was independently confirmed by the demonstration that a dominant-negative version of the kinase Pelle can block induction of drosomycin by the cytokine Spaetzle, but does not affect induction of the antibacterial peptide attacin by lipopolysaccharide.

Human interferon-gamma-mediated immunity is a genetically controlled continuous trait that determines the outcome of mycobacterial invasion.

Individuals with inherited disorders of interferon gamma (IFN-gamma)-mediated immunity appear to be specifically vulnerable to mycobacterial infections. The severity of clinical features of affected individuals differs between cases. Some patients die of mycobacterial infection in early childhood, whereas others have long asymptomatic periods in childhood and as adults. This rare syndrome also shows high allelic and non-allelic genetic heterogeneity. Mutations in IL12B, encoding the interleukin (IL)-12 p40 subunit, and in IL12RB1, encoding the beta1 chain of the IL-12 receptor, result in impaired IFN-gamma production. Mutations in IFNGR1 and IFNGR2, encoding the two IFN-gamma receptor chains, and mutations in STAT1, encoding an essential signaling component, result in impaired cellular responses to IFN gamma. Different types of mutation define two types of complete and two types of partial IFNgammaR1 deficiency. Complete and partial IFNgammaR2 deficiency have also been described. We herein compare the genotypes, cellular phenotypes, and clinical phenotypes of healthy individuals and patients with the seven known genetic disorders impairing cellular responses to IFN-gamma. Patients with defective IFN-gamma production were not considered in this study. The mutations and clinical features of patients with IFNgammaR1, IFNgammaR2, and STAT-1 deficiency are reviewed. Selected cell lines from each of the eight groups were tested for their response to IFN-gamma. We find that individuals may be classified into four broad groups based on genotype, cellular phenotype, and clinical phenotype (normal individuals and patients with mild, intermediate, or severe disease). This correlation suggests that IFN-gamma-mediated cell activation is a genetically controlled quantitative trait and that it determines the outcome of mycobacterial invasion in man.

Recurrent Mycobacterium avium osteomyelitis associated with a novel dominant interferon gamma receptor mutation.

Mycobacterium avium causes infections in immunocompromised individuals. Recurrent infection with this organism has been associated with a deletion at the 818 residue of the interferon-gamma receptor (IFN-gammaR). This mutation produces a truncated receptor without an intracytoplasmic tail, resulting in diminished signaling. We describe a substitution at the 832 residue of the IFN-gammaR causing a similar truncated receptor in a 7-year-old girl with recurrent M avium osteomyelitis.

Surface expression of the IFN-gamma R2 chain is regulated by intracellular trafficking in human T lymphocytes.

The surface and cytoplasmic expressions of the transducing chain (IFN-gamma R2) of the heterodimeric IFN-gamma receptor on human T lymphocytes have been investigated. We show that its surface expression is low, whereas high cytoplasmic levels are found in both resting and PHA-activated T lymphocytes. This low expression does not prevent activated T cells from responding to IFN-gamma, because it induces IFN-regulatory factor 1 expression. Low surface IFN-gamma R2 expression appears to be due to recycling between cytoplasmic stores and the cell surface, which does not depend on signals mediated by endogenous IFN-gamma, because IFN-gamma R2 surface expression is low, and its internalization is equally observed in patients with inherited IFN-gamma R1 gene deficiency and in healthy donors. Moreover, IFN-gamma R2 internalization in T lymphoblasts from healthy donors was not affected by the presence of anti-IFN-gamma-neutralizing or anti-IFN-gamma R1-blocking mAb. In conclusion, these data illustrate a new mechanism whereby human T cells limit the surface expression of IFN-gamma R2 in a ligand-independent manner.

Osteopontin expression correlates with clinical outcome in patients with mycobacterial infection.

Osteopontin (OPN) is a protein that is expressed in chronic inflammatory diseases including tuberculosis, and its deficiency predisposes to more severe mycobacterial infections in mice. However, no reports have identified altered OPN expression in, or correlated these alterations to, infections in humans. The data presented herein identify alterations in the tissue expression of OPN protein and describe an inverse correlation between these levels and disease progression after inoculation of Mycobacterium bovis bacillus Calmette-Guérin vaccine in humans. Patients with regional adenitis and good clinical outcomes had abundant OPN in infected lymph nodes. This pattern of OPN accumulation was also observed in patients infected by M. avium-intracellulare. In contrast, patients with disseminated infection and histologically ill-defined granulomas had no significant osteopontin accumulation in infected lymph nodes; these patients had either deficiencies in the interferon-gamma receptor 1 or idiopathic immune defects. The level of OPN protein expression was inversely correlated with disseminated infection and, of particular interest, with death of the patient. We conclude that osteopontin expression correlates with an effective immune and inflammatory response when humans are challenged by a mycobacterial infection and that osteopontin contributes to human resistance against mycobacteria.

Abnormal CD40-mediated activation pathway in B lymphocytes from patients with hyper-IgM syndrome and normal CD40 ligand expression.

The CD40-mediated activation pathway of B cells from 10 patients with hyper-IgM syndrome and normal expression of CD40 ligand was studied. In all 10 cases, B cells were found to be defective for IgG, IgA, and IgE production after stimulation by anti-CD40 mAbs and cytokines. In the patients tested, neither B cell proliferation (n = 6) nor CD23 molecule expression (n = 5) were observed in cultures stimulated with anti-CD40 mAb. These results point to an intrinsic B cell deficiency and a defect in the CD40-triggered B cell activation pathway; this conclusion was supported by a lack of detectable germinal centers in the spleen of two patients. CD40-triggered activation events, i.e., phosphatidylinositol 3 (PI3) kinase activation and induction of transcription factors NF-kappaB and AP-1, were next analyzed in B cell lines derived from five patients. Three distinct patterns were observed: an absence of detectable abnormalities (n = 1), defective PI3 kinase activation with normal induction of NF-kappaB and AP-1 (n = 3), and defects in both PI3 kinase activation and induction of NF-kappaB and AP-1 (n = 1). In three B cell lines, each exhibiting one of the CD40-mediated activation patterns, sequences of CD40 and CD40 binding protein coding regions were normal. The coding region of TNF receptor-associated factor 2 (TRAF2), which is known to interact with CD40 for NF-kappaB induction, was also found to be normal in B cell lines deficient in NF-kappaB induction. Altogether, these results suggest that CD40 ligand-positive hyper-IgM syndrome could be genetically heterogeneous, although phenotypic variability is not excluded, and that an early defect in the CD40-triggered activation cascade can account for defective Ig class switching in some patients with CD40 ligand-positive hyper-IgM syndrome.

Fatal disseminated Mycobacterium smegmatis infection in a child with inherited interferon gamma receptor deficiency.

Mycobacterium smegmatis is a common environmental mycobacterium that was first identified in 1884, yet is a rare pathogen in humans. The few M. smegmatis infections reported to date have been localized and have occurred in association with a primary lesion in otherwise immunocompetent individuals. To our knowledge, no case of disseminated M. smegmatis infection has ever been reported, even in patients with severe immune deficiencies. We report a case of disseminated mycobacterial infection that was diagnosed in a 3-year-old girl. The pathogen was not identified as M. smegmatis until the patient was 6 years old. Her condition gradually worsened, and she died when she was 8 years old despite appropriate antimycobacterial therapy. No other opportunistic infections were documented. Immunological investigations revealed an inherited interferon gamma receptor 1 deficiency. This report identifies M. smegmatis as a new opportunistic agent that may be responsible for disseminated disease in immunocompromised individuals.