Genetic susceptibility to herpes simplex virus 1 encephalitis in mice and humans

Functional genomics reveals an essential and specific role for Stat1 in protection of the central nervous system following herpes simplex virus corneal infection

Innate immune deficiencies result in a spectrum of severe clinical outcomes following infection. In particular, there is a strong association between loss of the signal transducer and activator of transcription (Stat) pathway, breach of the blood-brain barrier (BBB), and virus-induced neuropathology. The gene signatures that characterize resistance, disease, and mortality in the virus-infected nervous system have not been defined. Herpes simplex virus type 1 (HSV-1) is commonly associated with encephalitis in humans, and humans and mice lacking Stat1 display increased susceptibility to HSV central nervous system (CNS) infections. In this study, two HSV-1 strains were used, KOS (wild type [WT]), and Δvhs, an avirulent recombinant lacking the virion host shutoff (vhs) function. In addition, two mouse strains were used: strain 129 (control) and a Stat1-deficient (Stat1(-/-)) strain. Using combinations of these virus and mouse strains, we established a model of infection resulting in three different outcomes: viral clearance without neurological disease (Δvhs infection of control mice), neurological disease followed by viral clearance (Δvhs infection of Stat1(-/-) mice and WT infection of control mice), or neurological disease followed by death (WT infection of Stat1(-/-) mice). Through the use of functional genomics on the infected brain stems, we determined gene signatures that were representative of the three infection outcomes. We demonstrated a pathological signature in the brain stem of Stat1-deficient mice characterized by upregulation of transcripts encoding chemokine receptors, inflammatory markers, neutrophil chemoattractants, leukocyte adhesion proteins, and matrix metalloproteases. Additionally, there was a greater than 100-fold increase in the inflammatory markers interleukin 1β (IL-1β) and IL-6. Consistent with this gene signature, we demonstrated profound CNS inflammation with a concomitant lethal breach of the BBB. Taken together, our results indicated an essential role for normal Stat1-dependent signaling in mediating a nonpathological immune response to viral CNS infection.

Herpes simplex virus encephalitis in a patient with complete TLR3 deficiency: TLR3 is otherwise redundant in protective immunity

A new autosomal recessive form of complete TLR3 deficiency reveals that human TLR3 is nonredundant in immunity against herpes simplex virus 1 in the central nervous system (CNS) but redundant in host defense against viruses outside the CNS.

Autosomal dominant TLR3 deficiency has been identified as a genetic etiology of childhood herpes simplex virus 1 (HSV-1) encephalitis (HSE). This defect is partial, as it results in impaired, but not abolished induction of IFN-β and -λ in fibroblasts in response to TLR3 stimulation. The apparently normal resistance of these patients to other infections, viral illnesses in particular, may thus result from residual TLR3 responses. We report here an autosomal recessive form of complete TLR3 deficiency in a young man who developed HSE in childhood but remained normally resistant to other infections. This patient is compound heterozygous for two loss-of-function TLR3 alleles, resulting in an absence of response to TLR3 activation by polyinosinic-polycytidylic acid (poly(I:C)) and related agonists in his fibroblasts. Moreover, upon infection of the patient’s fibroblasts with HSV-1, the impairment of IFN-β and -λ production resulted in high levels of viral replication and cell death. In contrast, the patient’s peripheral blood mononuclear cells responded normally to poly(I:C) and to all viruses tested, including HSV-1. Consistently, various TLR3-deficient leukocytes from the patient, including CD14⁺ and/or CD16⁺ monocytes, plasmacytoid dendritic cells, and in vitro derived monocyte-derived macrophages, responded normally to both poly(I:C) and HSV-1, with the induction of antiviral IFN production. These findings identify a new genetic etiology for childhood HSE, indicating that TLR3-mediated immunity is essential for protective immunity to HSV-1 in the central nervous system (CNS) during primary infection in childhood, in at least some patients. They also indicate that human TLR3 is largely redundant for responses to double-stranded RNA and HSV-1 in various leukocytes, probably accounting for the redundancy of TLR3 for host defense against viruses, including HSV-1, outside the CNS.

NEMO is a key component of NF-κB- and IRF-3-dependent TLR3-mediated immunity to herpes simplex virus

BACKGROUND

Children with germline mutations in Toll-like receptor 3 (TLR3), UNC93B1, TNF receptor-associated factor 3, and signal transducer and activator of transcription 1 are prone to herpes simplex virus-1 encephalitis, owing to impaired TLR3-triggered, UNC-93B-dependent, IFN-α/β, and/or IFN-λ-mediated signal transducer and activator of transcription 1-dependent immunity.

OBJECTIVE

We explore here the molecular basis of the pathogenesis of herpes simplex encephalitis in a child with a hypomorphic mutation in nuclear factor-κB (NF-κB) essential modulator, which encodes the regulatory subunit of the inhibitor of the Iκβ kinase complex.

METHODS

The TLR3 signaling pathway was investigated in the patient's fibroblasts by analyses of IFN-β, IFN-λ, and IL-6 mRNA and protein levels, by quantitative PCR and ELISA, respectively, upon TLR3 stimulation (TLR3 agonists or TLR3-dependent viruses). NF-κB activation was assessed by electrophoretic mobility shift assay and interferon regulatory factor 3 dimerization on native gels after stimulation with a TLR3 agonist.

RESULTS

The patient's fibroblasts displayed impaired responses to TLR3 stimulation in terms of IFN-β, IFN-λ, and IL-6 production, owing to impaired activation of both NF-κB and IRF-3. Moreover, vesicular stomatitis virus, a potent IFN-inducer in human fibroblasts, and herpes simplex virus-1, induced only low levels of IFN-β and IFN-λ in the patient's fibroblasts, resulting in enhanced viral replication and cell death, as reported for UNC-93B-deficient fibroblasts.

CONCLUSION

Herpes simplex encephalitis may occur in patients carrying NF-κB essential modulator mutations, due to the impairment of NF-κB- and interferon regulatory factor 3-dependent-TLR3-mediated antiviral IFN production.

TLR7/9 versus TLR3/MDA5 signaling during virus infections and diabetes

IFN-I are pleiotropic cytokines that impact innate and adaptive immune responses. In this article, we discuss TLR7/9 versus TLR3/MDA5 signaling in antiviral responses and diabetes. pDCs are thought to have a critical role in antiviral defense because of their ability to rapidly secrete large amounts of IFN-I through TLR7/9 signaling. A recent study demonstrates that although pDCs are a source of IFN-I in vivo, their overall contribution to viral containment is limited and time-dependent, such that additional cellular sources of IFN-I are required to fully control viral infections. dsRNA sensors, such as TLR3 and MDA5, provide another important trigger for antiviral IFN-I responses, which can be exploited to enhance immune responses to vaccines. In the absence of infection, IFN-I production by pDCs or from signaling through dsRNA sensors has been implicated in the pathogenesis of autoimmune diseases such as diabetes. However, recent data demonstrate that IFN-I production via TLR3 and MDA5 is critical to counter diabetes caused by a virus with preferential tropism for pancreatic β-cells. This highlights the complexity of the host antiviral response and how multiple cellular and molecular components balance protective versus pathological responses.

Distribution, clinical features and treatment in Taiwanese patients with symptomatic primary immunodeficiency diseases (PIDs) in a nationwide population-based study during 1985-2010

Primary immunodeficiency diseases (PIDs) are a group of rare diseases with wide geographic and ethnic variations in incidence, prevalence, and distribution patterns. The aim of this study was to examine the distribution pattern and clinical spectrum of PIDs in Taiwan at a national referral institute. From 1985 to 2010, 215 patients from 183 families were diagnosed and grouped according to the updated classification of PIDs. Eighty-one (37.7%) patients had "other well-defined immunodeficiency syndromes", followed by "predominantly antibody deficiencies" (54 patients; 25.1%), "T- and B-cell immunodeficiencies" (34; 15.8%), "congenital defects of phagocytes" (25; 20.2%), "complement deficiencies" (15; 7.0%), and "disease in immune dysregulation" (5; 2.3%). The last category included two patients with Chediak-Higashi syndrome, and one each with familial hemophagocytosis, IPEX, and hypogammaglobulinemia and albinism. One female had cold-induced auto-inflammatory disease. There were no cases of "defects in innate immunity". Pseudomonas and Streptococcus pneumoniae were the two most identified microorganisms in septicemia (42.7%; 44/103 episodes). Stem cell transplantation was successful in 13 of 22 patients, while 34 patients (15.8%) died. Molecular defects were identified in 109 individuals (from 90 families). There were relatively fewer cases of "predominantly antibody deficiencies" due to there being only a few patients with adult-onset PIDs, implying certainty bias rather than ethnic variation. Awareness of under-diagnosis among physicians rather than pediatricians is vital for timely diagnosis and consequently adequate treatment.

Human TLRs and IL-1Rs in host defense: natural insights from evolutionary, epidemiological, and clinical genetics

Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs) have TIR intracellular domains that engage two main signaling pathways, via the TIR-containing adaptors MyD88 (which is not used by TLR3) and TRIF (which is used only by TLR3 and TLR4). Extensive studies in inbred mice in various experimental settings have attributed key roles in immunity to TLR- and IL-1R-mediated responses, but what contribution do human TLRs and IL-1Rs actually make to host defense in the natural setting? Evolutionary genetic studies have shown that human intracellular TLRs have evolved under stronger purifying selection than surface-expressed TLRs, for which the frequency of missense and nonsense alleles is high in the general population. Epidemiological genetic studies have yet to provide convincing evidence of a major contribution of common variants of human TLRs, IL-1Rs, or their adaptors to host defense. Clinical genetic studies have revealed that rare mutations affecting the TLR3-TRIF pathway underlie herpes simplex virus encephalitis, whereas mutations in the TIR-MyD88 pathway underlie pyogenic bacterial diseases in childhood. A careful reconsideration of the contributions of TLRs and IL-1Rs to host defense in natura is required.

Early ''relapse'' after herpetic encephalitis: extensive white matter lesions in an infant with interferon production deficit

Acute secondary neurological deterioration after herpes simplex encephalitis has been reported. An immune-mediated process is thought to be responsible for some cases. The authors report the case of an infant who presented with fever, irritability, and orofacial involuntary movements, 15 days after herpes encephalitis onset. Polymerase chain reaction for herpes simplex virus was negative, and the magnetic resonance imaging revealed extensive white matter lesions. Chorea appeared only 11 days later. Raised immunoglobulin G index with oligoclonal bands and spreading of white matter lesions corroborated an immune-mediated etiology. An interferon production deficit was also detected. This case alerts that this form of ''relapse'' appears earlier than previously reported. A high level of suspicion is needed in the presence of atypical neurological deterioration and early white matter lesions should be considered as a warning sign. This case is also relevant because it associates, for the first time, an immune-mediated ''relapse'' to an interferon production deficit.

Crystal ball - 2011

In this feature, leading researchers in the field of microbial biotechnology speculate on the technical and conceptual developments that will drive innovative research and open new vistas over the next few years.

Pharmacogenetic interaction analysis for the efficacy of systemic treatment in metastatic colorectal cancer

BACKGROUND

Pharmacogenetic markers related to drug metabolism and mechanisms of action could help to better select patients with metastatic colorectal cancer (mCRC) for treatment. Genetic interaction analysis is used as a rational tool to study the contribution of polygenic variation in relation to drug response.

PATIENTS AND METHODS

A selection of 17 polymorphisms in genes encoding drug targets, pathway molecules and detoxification enzymes was analyzed in 279 previously untreated mCRC patients treated with capecitabine, oxaliplatin and bevacizumab (CAPOX-B). Multifactor dimensionality reduction analysis was used to identify a genetic interaction profile for progression-free survival (PFS).

RESULTS

Median PFS was 10.9 [95% confidence interval (CI) 9.4-12.4] months. A genetic interaction profile consisting of the TYMS enhancer region and VEGF +405G>C polymorphisms was significantly associated with PFS. Median PFS was 13.3 (95% CI 11.4-15.3) and 9.7 (95% CI 7.6-11.8) months for the beneficial and unfavorable genetic profiles, respectively, corresponding to a hazards ratio for PFS of 1.58 (95% CI 1.14-2.19). None of the studied polymorphisms were individually associated with PFS.

CONCLUSIONS

Our results support a genetic interaction between the TYMS enhancer region and VEGF +405G>C polymorphisms as a predictor of the efficacy of CAPOX-B in mCRC patients.

Age-dependent Mendelian predisposition to herpes simplex virus type 1 encephalitis in childhood

OBJECTIVE

To test the hypothesis that predisposition to childhood herpes simplex virus (HSV) type 1 encephalitis (HSE) may be determined in part by human genetic factors.

STUDY DESIGN

A genetic epidemiologic survey of childhood HSE (onset at age 3 months to 15 years) over a 20-year period (1985-2004) was conducted throughout France (comprising 29 university hospital neuropediatric centers). A total of 85 children fulfilled the diagnostic criteria for inclusion. Family and personal histories were obtained by face-to-face interview for 51 patients.

RESULTS

No familial cases of HSE were identified in our survey; however, a high proportion (20%) of the children interviewed had a relevant family history: parental consanguinity (12% of patients), early-onset herpetic keratitis in a first-degree relative (6%), or both (2%). The narrow window of high susceptibility to HSE before age 3 years (62% of patients) further indicates that predisposition to HSE is tightly age-dependent.

CONCLUSIONS

This survey suggests that childhood HSE, although sporadic, may result from Mendelian predisposition (from autosomal recessive susceptibility in particular), at least in some children. There likely is incomplete penetrance, however, which may reflect, at least in part, the impact of age at the time of HSV-1 infection.

Toll-like receptor (TLR) 2 and TLR9 expressed in trigeminal ganglia are critical to viral control during herpes simplex virus 1 infection

Herpes simplex virus 1 (HSV-1) is a neurotropic DNA virus that is responsible for several clinical manifestations in humans, including encephalitis. HSV-1 triggers toll-like receptors (TLRs), which elicit cytokine production. Viral multiplication and cytokine expression in C57BL/6 wild-type (WT) mice infected with HSV-1 were evaluated. Virus was found in the trigeminal ganglia (TG), but not in the brains of animals without signs of encephalitis, between 2 and 6 days postinfection (d.p.i.). Cytokine expression in the TG peaked at 5 d.p.i. TLR9-/- and TLR2/9-/- mice were more susceptible to the virus, with 60% and 100% mortality, respectively, as opposed to 10% in the WT and TLR2-/- mice. Increased levels of both CXCL10/IP-10 and CCL2/MCP-1, as well as reduced levels of interferon-γ and interleukin 1-β transcripts, measured in both the TG and brains at 5 d.p.i., and the presence of virus in the brain were correlated with total mortality in TLR2/9-/- mice. Cytokine alterations in TLR2/9-/- mice coincided with histopathological changes in their brains, which did not occur in WT and TLR2-/- mice and occurred only slightly in TLR9-/- mouse brain. Increased cellularity, macrophages, CD8 T cells producing interferon-γ, and expression levels of TLR2 and TLR9 were detected in the TG of WT-infected mice. We hypothesize that HSV-1 infection is controlled by TLR-dependent immune responses in the TG, which prevent HSV-1 encephalitis.

Human herpesvirus 6 encephalitis

Human herpesvirus (HHV) 6, the etiologic agent of roseola, is nearly universally acquired during childhood. The virus establishes lifelong infection, including within the central nervous system (CNS), and replicates within several CNS cell types. HHV-6 has been linked to CNS disease during primary infection, including febrile seizures and possibly hippocampal injury. HHV-6 may also be associated with neurologic disease later in life, particularly in transplant patients. Recent reports offer evidence that HHV-6 reactivation may underlie a characteristic limbic encephalitis syndrome following hematopoietic cell transplant; the cardinal features of this syndrome include memory loss, insomnia, electroencephalographic evidence of temporal lobe seizure activity, MRI signal intensity abnormalities of the mesial temporal lobe, and the syndrome of inappropriate release of antidiuretic hormone. HHV-6 DNA is frequently detectable by nucleic acid amplification tests in the cerebrospinal fluid and peripheral blood upon symptom onset, which may provide a screening strategy in high-risk patients. Possible associations of HHV-6 with meningoencephalitis, mesial temporal lobe epilepsy, and multiple sclerosis in apparently immunocompetent hosts are under investigation.

The role of Toll-like receptor signaling in human immunodeficiencies

Through the last decade, clinical immunology has witnessed a considerable progress in understanding the role of the innate immunity in human host defense, with Toll-like receptors (TLRs) being the most extensively innate immune receptors investigated. Growing literature documents the relevance of TLR signaling pathways to human disease, revealing a small, but expanding, group of new monogenic primary immunodeficiencies, in patients with various infectious diseases, previously considered as of unexplained "idiopathic" origin. Herein, we review these recently described deficiencies. Autosomal recessive IRAK-4 and myeloid differentiation factor 88 deficiencies were reported in 2003 and 2008, respectively, conferring predisposition to pyogenic bacterial infections, and autosomal recessive UNC93B1 and autosomal dominant TLR3 deficiencies were reported in 2006 and 2007, respectively, conferring predisposition to herpes simplex encephalitis. Furthermore, we highlight the published data associating TLR polymorphism with an altered susceptibility to infectious diseases.

Fluoxetine and citalopram exhibit potent antiinflammatory activity in human and murine models of rheumatoid arthritis and inhibit toll-like receptors

OBJECTIVE

Selective serotonin reuptake inhibitors (SSRIs), in addition to their antidepressant effects, have been reported to have antiinflammatory effects. The aim of this study was to assess the antiarthritic potential of 2 SSRIs, fluoxetine and citalopram, in murine collagen-induced arthritis (CIA) and in a human ex vivo disease model of rheumatoid arthritis (RA).

METHODS

Following therapeutic administration of SSRIs, paw swelling was assessed and clinical scores were determined daily in DBA/1 mice with CIA. Joint architecture was examined histologically at the end of the treatment period. Cultures of human RA synovial membranes were treated with SSRIs, and cytokine production was measured. Toll-like receptor (TLR) function was examined in murine and human macrophages, human B cells, and human fibroblast-like synovial cells treated with SSRIs.

RESULTS

Both SSRIs significantly inhibited disease progression in mice with CIA, with fluoxetine showing the greatest degree of efficacy at the clinical and histologic levels. In addition, both drugs significantly inhibited the spontaneous production of tumor necrosis factor, interleukin-6, and interferon-gamma-inducible protein 10 in human RA synovial membrane cultures. Fluoxetine and citalopram treatment also inhibited the signaling of TLRs 3, 7, 8, and 9, providing a potential mechanism for their antiinflammatory action.

CONCLUSION

Fluoxetine and citalopram treatment selectively inhibit endosomal TLR signaling, ameliorate disease in CIA, and suppress inflammatory cytokine production in human RA tissue. These data highlight the antiarthritic potential of the SSRI drug family and provide further evidence of the involvement of TLRs in the pathogenesis of RA. The SSRIs may provide a template for potential antiarthritic drug development.

Attenuation of the influenza virus sickness behavior in mice deficient in Toll-like receptor 3

Certain sickness behaviors occur consistently in influenza-infected humans and mice. These include body temperature changes, somnolence, and anorexia. Several cytokines serve as mediators of the influenza acute phase response (APR), including these sickness behaviors, and one likely inducer of these cytokines is dsRNA produced during viral replication. TLR3 is known to be one of the host cellular components capable of recognizing dsRNA and activating cytokine synthesis. To determine the role of TLR3-detected viral dsRNA in the causation of viral symptoms, TLR3-deficient mice (TLR3 knockouts, or KOs) were infected with a marginally-lethal dose of mouse-adapted X-31 influenza virus. TLR3 KOs and their wild-type (WT) controls were monitored for baseline body temperature, locomotor activity, and sleep profiles prior to infection. Both mouse strains were then infected and monitored for changes in these sickness behaviors plus body weight changes and mortality for up to 14days post-infection. Consistent with the observations that influenza pathology is reduced in TLR3 KOs, we showed that hypothermia after post-infection day 5 and the total loss of body weight were attenuated in the TLR3 KOs. Sleep changes characteristic of this infection model [particularly increased non-rapid-eye-movement sleep (NREMS)] were also attenuated in TLR3 KOs and returned to baseline values more rapidly. Locomotor activity suppression was similar in both strains. Therefore virus-associated dsRNA detected by TLR3 appears to play a substantial role in mediating several aspects of the influenza syndrome in mice.

Laboratory evaluation of primary immunodeficiencies

Primary immunodeficiencies are congenital disorders caused by defects in different elements of the immune system. Affected patients usually present clinically with recurrent infections, severe infections, or both, as well as autoimmune phenomena that are associated with many of these disorders. Early diagnosis is essential for referral to specialized care centers and the prompt initiation of appropriate therapy. In this article the authors describe a general approach for the investigation of the most common primary immunodeficiencies, outlining the typical clinical symptoms and most appropriate laboratory investigations.

Viral infection leading to brain dysfunction: more prevalent than appreciated?

Virus infections of the brain can lead to transient or permanent neurologic or psychiatric dysfunction. Some of the complexities in establishing the causal role of viruses in brain disease are explored here.

Human genetics of infectious diseases: between proof of principle and paradigm

The observation that only a fraction of individuals infected by infectious agents develop clinical disease raises fundamental questions about the actual pathogenesis of infectious diseases. Epidemiological and experimental evidence is accumulating to suggest that human genetics plays a major role in this process. As we discuss here, human predisposition to infectious diseases seems to cover a continuous spectrum from monogenic to polygenic inheritance. Although many studies have provided proof of principle that infectious diseases may result from various types of inborn errors of immunity, the genetic determinism of most infectious diseases in most patients remains unclear. However, in the future, studies in human genetics are likely to establish a new paradigm for infectious diseases.

Persistence pays: how viruses promote host group survival

Recently, we have realized that viruses numerically dominate all life. Although viruses are known to affect host survival in populations, this has not been previously evaluated in the context of host group selection. Group selection per se is not a currently accepted idea and its apparent occurrence is explained by statistical gene frequency models of kin selection. Viruses were not considered in such models. Prevalent views associate viruses and disease. Yet many viruses establish species-specific persistent, inapparent infections that are stable on an evolutionary time scale. Such persistent infections can have large effects on relative reproductive fitness of competing host populations. In this essay, I present arguments on how persistent infections can promote population survival. Mouse hepatitis virus is used as well studied examplar to re-evaluate the theoretical basis of the mouse haystack model of M Smith. This virus-centric re-examination concludes that viruses can indeed affect and promote relative group selection.

ICAM-5 modulates cytokine/chemokine production in the CNS during the course of herpes simplex virus type 1 infection

Chemokines are important in HSE development in the CNS but underlying regulatory events are unknown. Two-hybrid binding assays identified that intercellular adhesion molecule 5 (ICAM-5), an immune modulator in the CNS, interacted with neurovirulence factor, UOL, of HSV-1. Viral load and interleukin levels were similar in UOL deletion virus (DeltaUOL), and wild type virus infected mouse brains. However, higher numbers of lymphocytes, but unaltered soluble ICAM-5 and chemokine levels were detected in DeltaUOL infected mouse brains. In contrast, lower lymphocyte numbers, reduced soluble ICAM-5, and higher chemokine levels were detected in wild type virus infected brains. Our results suggest that ICAM-5 plays a critical role in modulating chemokine production in the CNS.

From infectious diseases to primary immunodeficiencies

The field of primary immunodeficiencies has expanded, thanks to the exploration of novel clinical phenotypes and their connection with morbid genotypes, and the subsequent exploration of new patients who have known primary immunodeficiency-defining clinical phenotypes and their connection with novel morbid genotypes. This two-way process is becoming increasingly active, particularly for patients who have infectious diseases in whom the underlying immunologic and genetic causes remain mostly unexplained. The authors review how the exploration of children who have clinical infectious diseases caused by mycobacteria, pneumococcus, and herpes simplex virus recently led to the description of three new groups of primary immunodeficiencies. These three examples justify the continuation of the genetic exploration of novel infectious phenotypes and novel patients who have infections. This challenging process will eventually reap its rewards, to the benefit of patients and their families.

Revisiting human primary immunodeficiencies

Human primary immunodeficiencies (PIDs) are often thought to be confined to a few rare, familial, monogenic, recessive traits impairing the development or function of one or several leucocyte subsets and resulting in multiple, recurrent, opportunistic and fatal infections in infancy. We highlight here the rapidly growing number of exceptions to each of these conventional qualifications. Indeed, bona fide PIDs include common and sporadic illnesses and may present as dominant, or even polygenic traits; their pathogenesis may involve non haematopoietic cells, and they may result in single episode of illness, with a single or multiple morbid phenotypes, some of which may involve infection, in otherwise healthy adults. We need to increase awareness of the multitude of clinical presentations of human PIDs considerably and rapidly in the medical community. Human PIDs should be considered in a wide range of clinical situations.

Novel primary immunodeficiencies revealed by the investigation of paediatric infectious diseases

Human primary immunodeficiencies impairing myeloid and/or lymphoid cellular responses to activating receptors other than antigen receptors have recently been described in children with various infectious diseases. Germline mutations in NEMO and IKBA impair NF-kappaB-mediated signalling, at least in response to the stimulation of TLRs, IL-1Rs and TNFRs, and confer a broad predisposition to infections. Mutations in IRAK4 selectively impair TLRs other than TLR3 and most IL-1R responses, and confer a predisposition to pyogenic bacterial diseases, including invasive pneumococcal disease in particular. Mutations in TLR3 and UNC93B1 impair TLR3 responses and confer a predisposition to herpes simplex encephalitis. Mutations in STAT1 impair IFN-gamma and/or IFN-alpha/beta responses and predispose subjects to mycobacterial and viral diseases, respectively. Mutations in IFNGR1 and IFNGR2 impair IFN-gamma responses and confer a predisposition to mycobacterial diseases. Mutations in IL12B and IL12RB1 impair IL-12 and IL-23 responses and predispose subjects to infections caused by mycobacteria and Salmonella. Finally, mutations in TYK2 and STAT3 mostly impair IL-6R responses, conferring a predisposition to staphylococcal disease in particular. The infectious phenotypes associated with these novel leukocyte activation deficiencies are therefore collectively diverse, tightly dependent on the morbid gene and affected pathway, and individually narrow, often restricted to one or a few infectious diseases.