Cheng-Lung Ku

Inherited disorders of human Toll-like receptor signaling: immunological implications

Summary:  In vitro nine of 10 known human Toll‐like receptors (TLRs) are engaged by well‐defined chemical agonists that mimic microbial compounds, raising the possibility that human TLRs play a critical role in protective immunity in vivo. We thus review here the recently described human primary immunodeficiencies caused by germline mutations in genes encoding molecules involved in cell signaling downstream from TLRs. Subjects with anhidrotic ectodermal dysplasia with immunodeficiency (EDA‐ID) carry either X‐linked recessive hypomorphic mutations in NEMO or autosomal dominant hypermorphic mutations in IKBA. Their cells show a broad defect in nuclear factor‐κB (NF‐κB) activation, with an impaired, but not abolished response to a large variety of stimuli including TLR agonists. EDA‐ID patients show developmental anomalies of skin appendages and a broad spectrum of infectious diseases. Patients with autosomal recessive amorphic mutations in IRAK4 present a purely immunological syndrome and more restricted defects, with specific impairment of the Toll and interleukin‐1 receptor (TIR)–interleukin‐1 receptor‐associated kinase (IRAK) signaling pathway. In these subjects, the NF‐κB‐ and mitogen‐activated protein kinase‐mediated induction of inflammatory cytokines in response to TIR agonists is impaired. The patients present a narrow range of pyogenic bacterial infections that become increasingly rare with age. Altogether, these data suggest that human TLRs play a critical role in host defense. However, they do not provide compelling evidence, as even the infectious phenotype of patients with mutations in IRAK4 may result from impaired signaling via receptors other than TLRs. Paradoxically, these experiments of nature raise the possibility that the entire set of human TLRs is largely redundant in protective immunity in vivo.

Bacillus Calmette guérin triggers the IL-12/IFN-γ axis by an IRAK-4- and NEMO-dependent, non-cognate interaction between monocytes, NK, and T lymphocytes

The IL‐12/IFN‐γ axis is crucial for protective immunity to Mycobacterium in humans and mice. Our goal was to analyze the relative contribution of various human blood cell subsets and molecules to the production of, or response to IL‐12 and IFN‐γ. We designed an assay for the stimulation of whole blood by live M. bovis Bacillus Calmette‐Guérin (BCG) alone, or BCG plus IL‐12 or IFN‐γ, measuring IFN‐γ and IL‐12 levels. We studied patients with a variety of specific inherited immunodeficiencies resulting in a lack of leukocytes, or T, B, and/or NK lymphocytes, or polymorphonuclear cells, or a lack of expression of key molecules such as HLA class II, CD40L, NF‐κB essential modulator (NEMO), and IL‐1 receptor‐associated kinase‐4 (IRAK‐4). Patients with deficiencies in IL‐12p40, IL‐12 receptor β1 chain (IL‐12Rβ1), IFN‐γR1, IFN‐γR2, and STAT‐1 were used as internal controls. We showed that monocytes were probably the main producers of IL‐12, and that NK and T cells produced similar amounts of IFN‐γ. NEMO and IRAK‐4 were found to be important for IL‐12 production and subsequent IFN‐γ production, while a lack of CD40L or HLA class II had no major impact on the IL‐12/IFN‐γ axis. The stimulation of whole blood by live BCG thus triggers the IL‐12/IFN‐γ axis by an IRAK‐4‐ and NEMO‐dependent, non‐cognate interaction between monocytes, NK, and T lymphocytes.

The NEMO mutation creating the most-upstream premature stop codon is hypomorphic because of a reinitiation of translation.

Amorphic mutations in the NF- kappa B essential modulator (NEMO) cause X-dominant incontinentia pigmenti, which is lethal in males in utero, whereas hypomorphic mutations cause X-recessive anhidrotic ectodermal dysplasia with immunodeficiency, a complex developmental disorder and life-threatening primary immunodeficiency. We characterized the NEMO mutation 110_111insC, which creates the most-upstream premature translation termination codon (at codon position 49) of any known NEMO mutation. Surprisingly, this mutation is associated with a pure immunodeficiency. We solve this paradox by showing that a Kozakian methionine codon located immediately downstream from the insertion allows the reinitiation of translation. The residual production of an NH(2)-truncated NEMO protein was sufficient for normal fetal development and for the subsequent normal development of skin appendages but was insufficient for the development of protective immune responses.

NEMO Mutations in 2 Unrelated Boys With Severe Infections and Conical Teeth

X-linked recessive anhidrotic ectodermal dysplasia with immunodeficiency is a developmental and immunologic disorder caused by mutations in nuclear factor-κB essential modulator (NEMO), which is essential for nuclear factor-κB activation. Early in life, affected boys present a typical appearance, with hypotrichosis or atrichosis, hypohidrosis or anhidrosis, and hypodontia or anodontia with conical incisors. They are also susceptible to various microorganisms, mostly pyogenic bacteria and mycobacteria. Here we report 2 unrelated boys, aged 6 and 11 years, who have novel mutations in NEMO and present conical incisors and hypodontia as their sole and long-unrecognized developmental anomaly. One child had isolated recurrent pneumococcal disease, whereas the other had multiple infections. Our observations indicate that conical incisors should prompt the search for NEMO mutations in boys with unusual infectious diseases.

A Fast Procedure for the Detection of Defects in Toll-like Receptor Signaling

OBJECTIVES. Inborn defects in Toll-like receptor signaling are recently described primary immunodeficiencies that predispose affected children to life-threatening infections. Patients with interleukin-1 receptor-associated kinase-4 deficiency are prone to invasive pneumococcal disease, and patients with UNC-93B deficiency are prone to herpes simplex virus encephalitis. These genetic disorders are underdiagnosed, partly because diagnosis currently requires expensive and time-consuming techniques available at only a few specialized centers worldwide. We, therefore, aimed to develop a cheap and fast test for the detection of defects in Toll-like receptor signaling. PATIENTS AND METHODS. We used flow cytometry to evaluate the cleavage of membrane-bound L-selectin on granulocytes in 38 healthy controls and in 7 patients with genetically defined Toll-like receptor signaling defects (5 patients with interleukin-1 receptor-associated kinase-4 deficiency and 2 patients with UNC-93B deficiency), on activation with various Toll-like receptor agonists. RESULTS. Impaired L-selectin shedding was observed with granulocytes from all of the interleukin-1 receptor-associated kinase-4-deficient patients on activation with agonists of Toll-like receptors 1/2, 2/6, 4, 7, and 8 and with granulocytes from all of the UNC-93B-deficient patients on activation with agonists of Toll-like receptors 7 and 8. All of the healthy controls responded to these stimuli. CONCLUSIONS. The assessment of membrane-bound L-selectin cleavage on granulocytes by flow cytometry may prove useful for the detection of primary immunodeficiencies in the Toll-like receptor pathway, such as interleukin-1 receptor-associated kinase-4 deficiency and UNC-93B deficiency. This procedure is cheap and rapid. It may, therefore, be suitable for routine testing worldwide in children with invasive pneumococcal disease and in patients with herpes simplex encephalitis.

Isolated Congenital Asplenia: A French Nationwide Retrospective Survey of 20 Cases

OBJECTIVE To better describe the natural history, mode of inheritance, and the epidemiological and clinical features of isolated congenital asplenia, a rare and poorly understood primary immunodeficiency. STUDY DESIGN A French national retrospective survey was conducted in hospital pediatric departments. A definitive diagnosis of ICA was based on the presence of Howell-Jolly bodies, a lack of detectable spleen, and no detectable cardiovascular malformation. RESULTS The study included 20 patients (12 males and 8 females) from 10 kindreds neither related to each other nor consanguineous. The diagnosis of ICA was certain in 13 cases (65%) and probable in 7 cases (35%). Ten index cases led to diagnosis of 10 additional cases in relatives. Five cases were sporadic and 15 were familial, suggesting autosomal dominant inheritance. Median age was 12 months at first infection (range, 2-516 months), 11 months at diagnosis of asplenia (range, 0-510 months), and 9.9 years at last follow-up (range, 0.7-52 years). Fifteen patients sustained 18 episodes of invasive bacterial infection, caused mainly by Streptococcus pneumoniae (61%). Outcomes were poor, with 9 patients (45%) dying from fulminant infection. CONCLUSIONS ICA is more common than was previously thought, with an autosomal dominant inheritance in at least some kindreds. Relatives of cases of ICA should be evaluated for ICA, as should children and young adults with invasive infection.

Septicemia without Sepsis: Inherited Disorders of Nuclear Factor-kB-Mediated Inflammation

Septicemia is a life-threatening condition that may lead to sepsis and even septic shock. This cascade is usually accompanied by a pronounced inflammatory response, leading to high body temperature and elevated levels of laboratory markers of inflammation. However, this response can be significantly diminished in children with inherited disorders of nuclear factor (NF)-kappa B-mediated immunity. Three disease-causing genes involved in NF-kappa B activation have been identified: NEMO, IKBA, and IRAK4. Patients with anhidrotic ectodermal dysplasia and immunodeficiency, which is caused by mutations in NEMO and IKBA, have sparse hair, dry skin, and conical teeth and are at increased risk of severe infections caused by pyogenic bacteria and atypical mycobacteria. Patients with interleukin-1 receptor-associated kinase-4 deficiency are at increased risk of invasive disease due to pyogenic bacteria. An underlying defect in NF- kappa B activation should be suspected in children with bacterial septicemia accompanied by mild signs of inflammation.

Staphylococcal pericarditis, and liver and paratracheal abscesses as presentations in two new cases of interleukin-1 receptor associated kinase 4 deficiency.

Background: A deficiency in the interleukin-1 receptor activated kinase 4 (IRAK-4) has recently been associated with severe recurrent, predominantly Gram-positive bacterial infections. Clinical Presentation: Two unrelated Canadian children with unique presentations of IRAK-4 deficiency are described. Both children had multiple Gram-positive bacterial infections, specifically Staphylococcus aureus and Streptococcus pneumoniae. Although these microorganisms in patients with IRAK-4 deficiency commonly cause invasive infections, such as meningitis, arthritis, and sepsis, the sites of infection in our patients were unique. In the first patient, staphylococcal pericarditis and, on a separate occasion, staphylococcal liver abscesses with generalized peritonitis were presentations. In the second child, S. aureus infection caused submandibular and periauricular lymphadenitis with unsuspected paratracheal abscess as well. These severe infections were not accompanied by the expected constitutional symptoms or hematologic and acute phase responses despite findings of advanced infection on diagnostic imaging. Methods: Cytokine production [interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α] by whole blood leukocytes and adherent monocytes after stimulation with IL-1β or various Toll-like receptor agonists [lipopolysaccharide, Poly I:C, S. aureus peptidoglycan (PGN)] was analyzed. IRAK-4 genes were sequenced by standard techniques. Results: Failure by whole blood leukocytes to produce IL-6 or TNF-α in response to any of these stimuli was the most consistent finding. In striking contrast, IL-8 production in response to PGN was normal in both cases. Both patients had novel and heterozygous mutations and deletions in the IRAK-4 gene. Conclusions: Our results indicate that PGN-induced IL-6 production is via IRAK-4 dependent mechanisms, whereas IL-8 response to PGN is via IRAK-4 independent mechanisms. Patients with relatively silent but invasive bacterial infection should raise suspicion of IRAK-4 immunodeficiency.

Autosomal-dominant primary immunodeficiencies.

The vast majority of known primary immunodeficiencies (PIDs) are autosomal or X-linked recessive Mendelian traits. Only four classical primary immunodeficiencies are thought to be autosomal-dominant, three of which still lack a well-defined genetic etiology: isolated congenital asplenia, isolated chronic mucocutaneous candidiasis, and hyper IgE syndrome. The large deletions on chromosome 22q11.2 associated with Di George syndrome suggest that this disease may be dominant but not Mendelian, possibly involving several genes. The clinical and genetic features of six novel autosomal-dominant primary immunodeficiencies have however been described in recent years. These primary immunodeficiencies are caused by germline mutations in seven genes: ELA2, encoding a neutrophil elastase, and GFI1, encoding a regulator of ELA2 (mutations associated with severe congenital neutropenia); CXCR4, encoding a chemokine receptor (warts, hypogammaglobulinemia, infections and myelokathexis syndrome); LCRR8, encoding a key protein for B-cell development (agammaglobulinemia); IFNGR1, encoding the ligand-binding chain of the interferon-γ receptor; STAT1, encoding the signal transducer and activator of transcription 1 downstream from interferon-γR1 (Mendelian susceptibility to mycobacterial diseases); and IKBA, encoding IκBα, the inhibitor α of NF-κB (anhidrotic ectodermal dysplasia with immunodeficiency). These recent data suggest that many more autosomal-dominant PIDs are likely to be identified in the near future.