Viral infections in interferon-gamma receptor deficiency

Selective insufficiency of IFN-gamma secretion in patients with hyper-IgE syndrome

BACKGROUND

Hyper-immunoglobulin E (IgE) syndrome is a complex immune deficiency characterized by chronic eczematous dermatitis, recurrent staphylococcal infections, pneumatoceles, reduced neutrophil chemotaxis, and variably impaired T cell function. Although decreased interferon-gamma (IFN-gamma) production in patients with hyper-IgE syndrome is pointed out and known as a cause of reduced neutrophil chemotaxis, precise mechanism of their inadequate production of IFN-gamma remains unknown. To elucidate the pathogenesis of the defective production of IFN-gamma in patients with hyper-IgE syndrome, we assessed the in vitro production and secretion of IFN-gamma by peripheral blood mononuclear cells (PBMCs) from patients with hyper-IgE syndrome.

METHODS

Chemotaxis of neutrophils, mRNA levels of several cytokines, intracellular production and extracellular secretion of IFN-gamma, interleukin-2 (IL-2), and IL-4 by PBMCs from three patients with hyper-IgE syndrome were determined.

RESULTS

The transcription of IFN-gamma mRNA and the production of its protein molecules progressed normally. However, selective insufficiency in the secretion of IFN-gamma molecules was found in patients with hyper-IgE syndrome. Confocal laser scanning microscopy clearly demonstrated the accumulation of IFN-gamma in patients with hyper-IgE syndrome.

CONCLUSION

We demonstrated that there was a selective insufficiency in the secretion of IFN-gamma in patients with hyper-IgE syndrome. We hope that this fact would offer a new paradigm for understanding this disease.

Impaired response to interferon-alpha/beta and lethal viral disease in human STAT1 deficiency

The receptors for interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma activate components of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway, leading to the formation of at least two transcription factor complexes. STAT1 interacts with STAT2 and p48/IRF-9 to form the transcription factor IFN-stimulated gene factor 3 (ISGF3). STAT1 dimers form gamma-activated factor (GAF). ISGF3 is induced mainly by IFN-alpha/beta, and GAF by IFN-gamma, although both factors can be activated by both types of IFN. Individuals with mutations in either chain of the IFN-gamma receptor (IFN-gammaR) are susceptible to infection with mycobacteria. A heterozygous STAT1 mutation that impairs GAF but not ISGF3 activation has been found in other individuals with mycobacterial disease. No individuals with deleterious mutations in the IFN-alpha/beta signaling pathway have been described. We report here two unrelated infants homozygous with respect to mutated STAT1 alleles. Neither IFN-alpha/beta nor IFN-gamma activated STAT1-containing transcription factors. Like individuals with IFN-gammaR deficiency, both infants suffered from mycobacterial disease, but unlike individuals with IFN-gammaR deficiency, both died of viral disease. Viral multiplication was not inhibited by recombinant IFN-alpha/beta in cell lines from the two individuals. Inherited impairment of the STAT1-dependent response to human IFN-alpha/beta thus results in susceptibility to viral disease.

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.

Functional analysis of a promoter variant of the gene encoding the interferon-gamma receptor chain I

We analyzed a single nucleotide polymorphism (SNP) at position -56 (T-->C) in the promoter region of the gene encoding the human interferon-gamma receptor ligand-binding chain I (IFN-gammaR1). The mutation was present at similar frequencies in Gabonese children with either mild or severe malaria. Functional investigations of the promoter in a transfected human B-cell line showed lower levels of luciferase reporter gene expression in the presence of the mutation, indicating the importance of this position for promoter activity, and suggesting that this SNP might negatively influence the expression level of IFN-gammaR1 at the cell surface. Further examinations of the DNA sequence at this polymorphic site showed a perfectly matched binding site for the transcription factor activator protein 4 (AP-4) on both strands. Binding sites for other important transcription factors involved in gene expression and regulation of the immune response against infections, including Ikaros 2 (Ik-2), nuclear factor kappaB (NFkappaB), and CETS1p54, are also situated in this region.

The role of IFN-gamma in immune responses to viral infections of the central nervous system

Interferon (IFN)-gamma, is not only a marker of T(H)1 CD4, CD8 and natural killer (NK) cells, it is also a critical antiviral mediator which is central to the elimination of viruses from the CNS. In this review, we describe IFN-gamma, its receptor, signal transduction from receptor engagement, and antiviral downstream mediators. We demonstrate that although neurons are post-mitotic and non-renewing, they respond to IFN-gamma in a fashion similar to peripheral fibroblasts or lymphocytes. We have illustrated this review with details about studies on the role(s) of IFN-gamma in the pathogenesis of measles virus (MV), herpes simplex virus (HSV) type 1, and vesicular stomatitis virus (VSV) infections of the CNS. For VSV infection, IFN-gamma signals through Jaks 1 and 2 and STAT1 to activate (interferon regulatory factor) IRF-1; although viral protein synthesis is inhibited, PKR is not a critical mediator in the antiviral response to VSV in murine neurons. In contrast, induction of nitric oxide synthase (NOS) type 1 and its production of nitric oxide is essential in the elimination of viruses from neurons.

Correction of complete interferon-gamma receptor 1 deficiency by bone marrow transplantation

Complete interferon-gamma receptor 1 (IFNgammaR1) deficiency is a primary immunodeficiency disease characterized by high susceptibility to recurrent, severe mycobacterial and other intracellular infections. We here report the first successful treatment of the disorder by bone marrow transplantation (BMT). The 8-year-old girl had suffered from recurrent mycobacterial infections in the past and had developed liver cirrhosis with portal hypertension. For conditioning, fractionated total body irradiation (TBI) was used in combination with cyclophosphamide and antithymocyte globulin (ATG). The patient received red cell-depleted bone marrow from her HLA-identical sister. The transplantation course was uneventful and 4 years later, the child remains in excellent clinical condition and free of mycobacterial infections. She has stable mixed lymphohematopoietic chimerism after repeat T-cell transfusions. Liver disease has not further deteriorated. This experience shows that correction of IFNgammaR1 deficiency is possible by BMT and complications of the disease can be controlled.

Human natural killer cell deficiencies and susceptibility to infection

There are a surprisingly large number of human natural killer (NK) cell deficiency states that provide insight into the role of NK cells in defense against human infectious disease. Many disorders associated with NK cell defects are caused by single gene mutations and, thus, give additional understanding concerning the function of specific molecules in NK cell development and activities. A resounding theme of NK cell deficiencies is susceptibility to herpesviruses, suggesting that unexplained severe herpesviral infection should raise the possibility of an NK cell deficit.

Divergent role for TNF-alpha in IFN-gamma-induced killing of Toxoplasma gondii and Salmonella typhimurium contributes to selective susceptibility of patients with partial IFN-gamma receptor 1 deficiency

Patients with defects in IFN-gamma- or IL-12-mediated immunity are susceptible to infections with Salmonella and non-tuberculous mycobacteria, but rarely suffer from infections with other intracellular pathogens such as Toxoplasma gondii. Here we describe macrophage and T cell function in eight individuals with partial IFN-gamma receptor 1 (IFN-gammaR1) deficiency due to a mutation that results in elevated cell surface expression of a truncated IFN-gammaR1 receptor that lacks the intracellular domain. We show that various effector mechanisms dependent on IFN-gammaR signaling are affected to different extents. Whereas TNF-alpha production was normally up-regulated in response to IFN-gamma, IL-12 production and CD64 up-regulation were strongly reduced, and IFN-gamma-mediated killing of the intracellular pathogens Salmonella typhimurium and T. gondii was completely abrogated in patient's macrophages. Since these patients suffer selectively from infections with non-tuberculous mycobacteria and Salmonella, but not T. gondii, despite sero-immunity in six of eight patients, which indicates previous contact with this pathogen, we next studied the role of TNF-alpha as a possible immune compensatory mechanism. IFN-gamma-induced killing of T. gondii appeared to be partially mediated by TNF-alpha, and addition of TNF-alpha could compensate for the abrogated killing of T. gondii in the patient's macrophages. In contrast, IFN-gamma-mediated killing of S. typhimurium appeared to be independent of TNF-alpha. We propose that the divergent role of TNF-alpha in IFN-gamma-induced killing of T. gondii and S. typhimurium may at least partially explain the highly selective susceptibility of patients.

White blood cell defects: molecular discoveries and clinical management

In this review, we present the most recent discoveries at the molecular level in white blood cell defects, and explain how their identification helped us to understand the underlying pathophysiology and directed our approach in clinical management. These lately discovered genes, relevant to immune disorders of mononuclear phagocytes and neutrophils, include defects in the interferon gamma (IFNg)/interleukin 12 (IL-12) pathway, such as IFNg receptor (IFNgR) defects, IL-12 defect, IL-12 receptor (IL-12R) defect, and signal transducer and activator of transcription 1 (STAT-1) defect. We have also included NF-kappaB essential modifier (NEMO) defects, which lead to X-linked ectodermal dysplasia, with or without lymphedema and osteopetrosis, and a wide range of involvement of the immune system, which can mimic the hyper-IgM phenotype. Neutrophil-specific granule deficiency and neutrophil elastase deficiency are discussed, the latter being the molecular defect in both cyclic neutropenia and in some sporadic cases of severe congenital neutropenia.

Genetics, cytokines and human infectious disease: lessons from weakly pathogenic mycobacteria and salmonellae

Host genetic factors are important in determining the outcome of infections caused by intracellular pathogens, including mycobacteria and salmonellae, but until now have been poorly characterized. Recently, some individuals with severe infections due to otherwise weakly pathogenic mycobacteria (non-tuberculous mycobacteria or Mycobacterium bovis bacille Calmette-Guérin) or Salmonella species have been shown to be unable to produce or respond to interferon-gamma. This inability results from mutations in any of five genes encoding essential proteins of the type 1 cytokine cascade: interleukin-12p40, interleukin-12R beta 1, interferon-gamma R1, interferon-gamma R2 or STAT1. Ten syndromes have thus far been identified. Recent insights in genetically controlled host defense and susceptibility to mycobacterial disease are discussed.

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.

Inherited disorders of IL-12- and IFNgamma-mediated immunity: a molecular genetics update

In the last 6 years, considerable advances have been made in the molecular analysis of a rare clinical syndrome: Mendelian susceptibility to mycobacterial disease (MSMD). Infection with poorly virulent environmental non-tuberculous mycobacteria (NTM) or vaccination with bacillus Calmette-Guerin (BCG) may cause disseminating and even fatal disease in individuals suffering from this syndrome. Mutations in five genes (IFNGR1, IFNGR2, STAT1, IL12B and IL12RB1) have been shown to be responsible for MSMD and further allelic heterogeneity accounts for the existence of nine distinct inherited disorders. All of these disorders are caused by impaired IFNgamma-mediated immunity. These results have important medical and biological implications. In this report, we update the disease-causing mutations reported in the literature.

Host susceptibility factors in mycobacterial infection. Genetics and body morphotype

Through identification and evaluation of mutations and polymorphisms in components of the IFN gamma response pathways, a better understanding of the mechanisms and risk factors influencing the development of mycobacterial disease is gained. This may lead the way for development of therapeutic and preventative strategies. Although conventional science has focused on identifying discrete mutations, greater awareness of the impact of subtle changes, both at the genetic (polymorphisms) and physical levels (body morphotype), may prove critical in the investigative process. There has been extraordinary progress in the understanding of mycobacterial susceptibility factors over the last few years. The recognition of characteristic phenotypes will lead to the identification of new genetic bases for disease.

Inherited interleukin-12 deficiency: IL12B genotype and clinical phenotype of 13 patients from six kindreds

Interleukin-12 (IL12) is a cytokine that is secreted by activated phagocytes and dendritic cells and that induces interferon-gamma production by natural-killer and T lymphocytes. It consists of two subunits, p35 and p40, which are encoded by IL12A and IL12B, respectively. The first reported patient with a genetic cytokine disorder was a Pakistani child, who was homozygous for a large loss-of-function deletion (g.482+82_856-854del) in IL12B. This IL12-deficient child suffered from infections caused by bacille Calmette-Guérin (BCG) and Salmonella enteritidis. We herein report 12 additional patients from five other kindreds. In one kindred from India, the same large deletion that was described elsewhere (g.482+82_856-854del) was identified. In four kindreds from Saudi Arabia, a recessive loss-of-function frameshift insertion (g.315_316insA) was found. A conserved haplotype encompassing the IL12B gene suggested that a founder effect accounted for the recurrence of each mutation. The two founder mutational events-g.482+82_856-854del and g.315_316insA-were estimated to have occurred approximately 700 and approximately 1,100 years ago, respectively. Among a total of 13 patients with IL12 deficiency, 1 child had salmonellosis only and 12 suffered from clinical disease due to BCG or environmental nontuberculous mycobacteria. One patient also had clinical disease caused by virulent Mycobacterium tuberculosis, five patients had clinical disease caused by Salmonella serotypes, and one patient had clinical disease caused by Nocardia asteroides. The clinical outcome varies from case to case, since five patients (aged 2-11 years) died of overwhelming infection, whereas eight patients (aged 3-12 years) are still in good health and are not currently taking antibiotics. In conclusion, IL12 deficiency is not limited to a single kindred, shows significant variability of outcome, and should be considered in the genetic diagnosis of patients with mycobacteriosis and/or salmonellosis. To date, two founder IL12B mutations have been identified, accounting for the recurrence of a large deletion and a small insertion within populations from the Indian subcontinent and from the Arabian Peninsula, respectively.

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.

Mycobacterial diseases in primary immunodeficiencies

Primary immunodeficiency diseases comprise over 100 conditions, each associated with a variety of viral, bacterial, fungal and protozoan infections. M. tuberculosis and less virulent mycobacteria, such as bacille Calmette-Guérin vaccines and environmental non-tuberculous mycobacteria, may cause severe disease in patients with primary immunodeficiency diseases. However, no previous review has dealt with the issue of which primary immunodeficiency diseases predispose affected individuals to mycobacterial disease. This information is very useful, not only increasing our understanding of human immunity to mycobacteria, but also for the diagnostic investigation of patients with mycobacteriosis. We review here the medical literature on cases of mycobacterial disease in patients with primary immunodeficiency diseases.

Impaired interferon gamma-mediated immunity and susceptibility to mycobacterial infection in childhood

Mendelian susceptibility to poorly virulent mycobacteria such as bacillus Calmette-Guerin (BCG) and environmental nontuberculous mycobacteria is a clinically heterogeneous syndrome. The clinical features of affected children cover a continuous spectrum from disseminated lethal bacillus Calmette-Guerin infection to local recurrent nontuberculous mycobacterial infection. Different types of mutations in four genes (IFNGR1, IFNGR2, IL12B, IL12RB1) have revealed both allelic and nonallelic heterogeneity and result in eight different disorders whose common pathogenic pathway is impaired interferon gamma (IFNgamma) mediated immunity. The severity of the clinical phenotype depends on the genotype. Complete IL-12 p40 and IL-12 receptor beta1 deficiencies and partial IFNgamma receptor 1 (IFNgammaR1) and IFNgammaR2 deficiencies generally lead to curable infections at various ages, and antibiotics supplemented with IFNgamma if required are likely to be effective. Complete IFNgammaR1 and IFNgammaR2 deficiencies predispose to overwhelming infection in early childhood, which may respond to antibiotics but relapse when antibiotics are discontinued. Rapid discrimination between complete IFNgammaR1 and IFNgammaR2 deficiency and other defects, therefore, is an important diagnostic step for planning clinical management.

Differential effects of parainfluenza virus type 3 on human monocytes and dendritic cells

To understand the lack of protective immunity observed after infection with parainfluenza virus type 3 (PIV3), we tested the effect of the virus on human monocytes and monocyte-derived immature dendritic cells (DCs). Expression of viral antigens on the cell surfaces correlated with replication of the virus, which was marginal in monocytes but extremely efficient in DCs. The virus increased monocyte survival at least in part through the production of granulocyte-macrophage colony-stimulating factor but, in contrast, accelerated DC apoptosis. In addition, PIV3 infection failed to activate monocytes but induced maturation of DCs with increased expression of CD54, HLA-DR, CD86, and CD83 and production of bioactive IL-12. However, PIV3-infected DCs demonstrated low stimulatory properties in DC-T cell cocultures, a finding that could not be attributed to the production of infectious virus or IL-10. These results demonstrate for the first time that PIV3 dramatically modifies the survival and/or the function of antigen-presenting cells and might therefore prevent the development of efficient antiviral immune responses.

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.

Immune deficiency presenting as mycobacterial infection

All the discrete genetic defects identified to date that seem to specifically predispose to infection with NTM or BCG have occurred in the pathways involving the generation of or response to IFN-gamma (Fig. 3). This natural genetic survey therefore suggests that one of the most critical cytokines in the control of NTM and BCG is IFN-gamma. Unfortunately, this recognition does not give us a clear sense of the critical mechanism(s) involved and still leaves us at a phenomenological level of understanding. Therefore, even though IFN-gamma appears to be the most critical cytokine in the control of mycobacteria by the "experiments of nature" cited earlier, it is likely that other cytokines are involved in the more proximal events of killing of intracellular parasites and viral control. These cytokines or chemokines may perform better therapeutically than [figure: see text] does IFN-gamma if they are better able to evoke the critical antimycobacterial mechanism(s). Dissection of these pathways, identification of the most proximal factors, and exploitation of these findings for the treatment of mycobacterial and other intracellular infections is the critical charge for the future.

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.

Th1 T-cell and monocyte defects

Mutations predisposing to infections with intracellular pathogens and affecting Th1 T-cells and monocytes have been identified in the past few years. In this article, the authors review the interaction of T cells and monocytes in the context of host defense against intracellular pathogens. Known genetic defects in these pathways are summarized.

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.

Respiratory syncytial virus infection in patients with phagocyte defects

Patients with phagocyte defects frequently develop bacterial or fungal pneumonias, but they are not considered to be at increased risk for viral infections. We describe 3 patients with known phagocyte immunodeficiencies who developed lower respiratory tract infections (LRTI) caused by respiratory syncytial virus (RSV). All 3 patients had dense pneumonias as indicated by computed tomography scan of the lungs and RSV was recovered. We conclude that RSV can present as a dense pneumonia in patients with phagocyte defects. Along with common pathogens causing LRTI, RSV should be considered in the differential diagnosis. Viral cultures as well as rapid antigen detection assays for respiratory viruses should be included in the evaluation of LRTI in patients with phagocyte defects. respiratory syncytial virus, phagocyte, immunodeficiency, pneumonia.

Infection in patients with primary immunodeficiency disorders

Recent advances in the understanding of the molecular basis of primary immunodeficiency disorders are reviewed, with particular emphasis on how these provide insights to the normal host's handling of particular microbes. Also reviewed are a number of reports on series of patients with these disorders, documenting the incidence and nature of the infective complications that occur and the effectiveness of treatment strategies.

Cytokines and T cells in host defense

Soluble and cell-bound ligands profoundly influence the differentiative fate of lymphocytes during an immune response. Recent advances have been made in understanding the role of cytokine signals and costimulatory signals in the regulation of T cell responses associated with resistance or susceptibility to infection. There has also been recent progress in defining the requirements for the generation and maintenance of immunologic memory, a critical component of adaptive immunity.

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.