Isao Miyairi

Human Genetic Factors and Respiratory Syncytial Virus Disease Severity

SUMMARY To explain the wide spectrum of disease severity caused by respiratory syncytial virus (RSV) and because of the limitations of animal models to fully parallel human RSV disease, study of genetic influences on human RSV disease severity has begun. Candidate gene approaches have demonstrated associations of severe RSV in healthy infants with genetic polymorphisms that may alter the innate ability of humans to control RSV (surfactants, Toll-like receptor 4, cell surface adhesion molecules, and others) and those that may control differences in proinflammatory responses or enhanced immunopathology (specific cytokines and their receptors). These studies are reviewed. They are valuable since an understanding of the direction of a polymorphisms effect can help construct a meaningful human RSV disease pathogenesis model. However, the direction, degree, and significance of the statistical association for any given gene are equivocal among studies, and the functional significance of specific polymorphisms is often not even known. Polymorphism frequency distribution differences associated with RSV infection arising from diversity in the genetic background of the population may be confounded further by multiple-hypothesis testing and publication bias, as well as the investigators perceived importance of a particular pathogenic disease process. Such problems highlight the limitation of the candidate gene approach and the need for an unbiased large-scale genome-wide association study to evaluate this important disease.

The p47 GTPases Iigp2 and Irgb10 Regulate Innate Immunity and Inflammation to Murine Chlamydia psittaci Infection

C57BL/6J mice were 105-fold more resistant to Chlamydia psittaci infection than DBA/2J mice by LD100 determinations. Linkage analysis using BXD recombinant inbred strains revealed a single effector locus at a 1.5-Mbp region on chromosome 11 encoding a cluster of three p47 GTPases (Irgb10, Igtp, and Iigp2). Western blots of infected tissue showed that Irgb10 was elevated in resistant mice and one of the two possible Iigp2 protein isoforms was preferentially expressed in susceptible mice. The BXD39 strain, susceptible at Irgb10 and resistant at Iigp2, had an intermediate phenotype implicating the nonredundant role of these p47 GTPases. C57BL/6J and DBA/2J exhibited a difference in IFN-γ-dependent chlamydial control, which was reversible by Iigp2 small interfering RNA knockdown. Microarrays of infected peritoneal lavage revealed >10-fold up-regulation of neutrophil-recruiting chemokines in susceptible mice and >100-fold increase in macrophage differentiation genes in resistant mice, indicating that the susceptibility pattern involves the stimulation of different inflammatory cell-recruiting pathways. Massive neutrophil recruitment was seen in susceptible mice by histology and flow cytometry, and neutrophil chemokine receptor (CXCR2) knockout mice on a susceptible background survived a lethal challenge, confirming that neutrophil recruitment was required for susceptibility. Congenic Igtp knockout mice also susceptible at Irgb10 and Iigp2 on a resistant background recruited neutrophils and succumbed to infection. We conclude that Irgb10 and Iigp2 act together to confer differential susceptibility against murine chlamydial infection. Data indicate that these p47 GTPases have cell-autonomous effects that result in vastly different inflammatory stimulations, leading to either recovery or death.

Sustained generation of nitric oxide and control of mycobacterial infection requires argininosuccinate synthase 1

Nitric oxide (NO) defends against intracellular pathogens, but its synthesis must be regulated due to cell and tissue toxicity. During infection, macrophages import extracellular arginine to synthesize NO, generating the byproduct citrulline. Accumulated intracellular citrulline is thought to fuel arginine synthesis catalyzed by argininosuccinate synthase (Ass1) and argininosuccinate lyase (Asl), which would lead to abundant NO production. Instead, we find that citrulline is exported from macrophages during early stages of NO production with <2% retained for recycling via the Ass1-Asl pathway. Later, extracellular arginine is depleted, and Ass1 expression allows macrophages to synthesize arginine from imported citrulline to sustain NO output. Ass1-deficient macrophages fail to salvage citrulline in arginine-scarce conditions, leading to their inability to control mycobacteria infection. Thus, extracellular arginine fuels rapid NO production in activated macrophages, and citrulline recycling via Ass1 and Asl is a fail-safe system that sustains optimum NO production.

Duration of Untreated Chlamydial Genital Infection and Factors Associated with Clearance: Review of Animal Studies

Chlamydia trachomatis is an important cause of sexually transmitted infection that can manifest as acute cervicitis, pelvic inflammatory disease, and most commonly, chronic asymptomatic infection. The basis of this wide spectrum of manifestations and the factors that lead to clearance or chronic infection are poorly understood. We reviewed specific literature pertaining to clearance of primary genital tract infections in animal models, including mice, guinea pigs, pigs, sheep, and nonhuman primates. T helper 1 cell responses involved in cell-mediated immunity are key immune parameters that define efficient clearance in the murine and guinea pig models of chlamydial infection, which are useful for studying C. trachomatis clearance. However, there may be some differences between humans and other animals in innate and adaptive immune responses to chlamydial infection. Studies have suggested that differences in the induced T cell subsets and the species-specific differences in interferon gamma-mediated effector mechanisms may play a significant role in these discrepancies. To close these gaps in knowledge, translational research in humans is a critical next step. However, for questions about specific mechanisms of host-pathogen interaction that cannot be answered feasibly or ethically in humans, animal models will continue to be important. Future research should include use of humanized and nonmurine models that establish prolonged infection to improve understanding of chronic human infections.

Different Growth Rates of Chlamydia trachomatis Biovars Reflect Pathotype

BACKGROUND Despite small genomic differences, Chlamydia trachomatis biovars exhibit diverse disease manifestations and different growth rates in vivo and in cell culture models. METHODS Chlamydial inclusion-forming units were enumerated over time in HeLa cells, to evaluate the length of the developmental cycle for C. trachomatis strains A, B, C, and E/Bour (ocular strains) as well as D, E/UW5/Cx, F, and L2 (genital strains). Prototype strains A, D, and L2 were selected for detailed analysis of reticulate body growth, division, and genomic replication. The impact that changing host cells and that coinfection with different strains has on growth was also assessed. RESULTS The genital strains completed the developmental cycle in 36-44 h, whereas the ocular strains lagged behind considerably. Differences were the result of a longer lag phase (entry plus differentiation) and generation time for the ocular strains. A prototype ocular strain grew faster in conjunctival cells than in cervical cells. Coinfection with genital (D or L2) and ocular strains expedited recovery of the ocular strain. CONCLUSIONS Precise temporal evaluation of the chlamydial developmental cycle for selected genital and ocular C. trachomatis biovars provides a means for investigating genomic differences that define chlamydial pathotype.

Effective and safe immunizations with live-attenuated vaccines for children after living donor liver transplantation.

Immunizations using live-attenuated vaccines are not recommended for post-liver transplant children due to its theoretical risks. However, they will encounter vaccine-preventable viral diseases upon returning to real-life situations. We performed a total of 70 immunizations with four individual live-attenuated vaccines to 18 pediatric post-living donor liver transplant (LDLT) recipients who fulfilled a clinical criteria including humoral and cell-mediated immunity. The seroconversion rates at the first dose for measles (strain AIK-C), rubella (strain TO-336), varicella (strain Oka), and mumps (strains Hoshino) were 100% (15/15), 100% (15/15), 82% (9/11), and 82% (9/11), respectively. During observed period (-5 years 11 months), a few cases with waning immunity (antibodies were once produced but the levels fell over time) were seen except after rubella immunization. Clinical diseases after seroconversion or definite serious adverse effects due to immunization were not observed. Immunizations using selected live-attenuated vaccines were safe and effective for post-LDLT children who were not severely immunosuppressed.

Dermatologic manifestations of human parechovirus type 3 infection in neonates and infants.

Background: Human parechovirus type 3 (HPeV3) infection can cause sepsis-like syndrome and meningoencephalitis in neonates and young infants. Although maculopapular rash is a reported clinical manifestation of HPeV3 infection, the frequency and detailed characteristics of rash in neonates and young infants with HPeV3 infection are unknown. Methods: We retrospectively reviewed the clinical characteristics of neonates and young infants who received a diagnosis of HPeV3 infection on the basis of real-time polymerase chain reaction analysis of serum and/or cerebrospinal fluid specimens at the National Center for Child Health and Development in Tokyo between November 2010 and September 2011. Results: Fifteen neonates and young infants were diagnosed as having HPeV3 infection; median age was 33 days (range: 10–81 days). The most common clinical presentation on admission was fever (80%), the median duration of which was 3 days (range: 1–4 days). Five (33%) children required admission to the intensive care unit for close observation, and 2 (13%) required mechanical ventilation for cardiovascular instability. After hospitalization, all children developed rash, mainly on the extremities, at a mean of 3 days (range: 1–5 days) after fever onset. The most striking finding was that 80% (12/15) of patients developed a distinctive palmar–plantar erythematous rash, which disappeared after a median of 3 days (range: 2–7 days). All patients were discharged from hospital without serious sequelae. Conclusions: Palmar–plantar erythema in febrile neonates and young infants may be a diagnostic clue of HPeV3 infection.

Neonatal invasive group A streptococcal disease: case report and review of the literature.

We present a fatal case of neonatal invasive group A streptococcal disease and review of the literature. Twenty-four cases were early onset disease and were associated with concurrent maternal infection, respiratory distress, pneumonia, toxic shock-like syndrome and serotype M1. Fifteen cases were late onset disease associated with soft tissue infections and meningitis. Maternal carriage was identified as an important factor in neonatal group A streptococcal disease.

Chlamydia psittaci Genetic Variants Differ in Virulence by Modulation of Host Immunity

BACKGROUND Psittacosis is a zoonosis caused by Chlamydia psittaci and is characterized by severe pneumonia and systemic infection. We sought to determine the basis of the 1000-fold difference in lethal dose of 2 C. psittaci 6BC strains in mice. METHODS Genomes of the strains were sequenced. Mice were infected intraperitoneally and the growth kinetics, immune responses, and pathology were compared. RESULTS The 2 strains differed by the presence of a 7.5-kb plasmid in the attenuated strain and 7 nonsynonomous single-nucleotide polymorphisms between the chromosomes, including a serine/threonine protein kinase gene pkn5. The plasmid was cured from the attenuated strain, but it remained nonlethal. Strains did not differ in growth kinetics in vitro or in vivo. Infection with the attenuated strain led to influx of activated macrophages with relatively minor organ damage. In contrast, the virulent strain caused an influx of nonactivated macrophages, neutrophils, and significant end organ damage. Mice infected with the virulent strain survived challenge when coinfected with either the plasmid-positive or plasmid-negative attenuated strain, indicating that an active process elicited by the attenuated strain reduces inflammation and disease. CONCLUSIONS C. psittaci modulates virulence by alteration of host immunity, which is conferred by small differences in the chromosome.

Host genetics and Chlamydia disease: prediction and validation of disease severity mechanisms.

Genetic mapping studies may provide association between sequence variants and disease susceptibility that can, with further experimental and computational analysis, lead to discovery of causal mechanisms and effective intervention. We have previously demonstrated that polymorphisms in immunity-related GTPases (IRG) confer a significant difference in susceptibility to Chlamydia psittaci infection in BXD recombinant mice. Here we combine genetic mapping and network modeling to identify causal pathways underlying this association. We infected a large panel of BXD strains with C. psittaci and assessed host genotype, IRG protein polymorphisms, pathogen load, expression of 32 cytokines, inflammatory cell populations, and weight change. Proinflammatory cytokines correlated with each other and were controlled by a novel genetic locus on chromosome 1, but did not affect disease status, as quantified by weight change 6 days after infection In contrast, weight change correlated strongly with levels of inflammatory cell populations and pathogen load that were controlled by an IRG encoding genetic locus (Ctrq3) on chromosome 11. These data provided content to generate a predictive model of infection using a Bayesian framework incorporating genotypes, immune system parameters, and weight change as a measure of disease severity. Two predictions derived from the model were tested and confirmed in a second round of experiments. First, strains with the susceptible IRG haplotype lost weight as a function of pathogen load whereas strains with the resistant haplotype were almost completely unaffected over a very wide range of pathogen load. Second, we predicted that macrophage activation by Ctrq3 would be central in conferring pathogen tolerance. We demonstrated that macrophage depletion in strains with the resistant haplotype led to neutrophil influx and greater weight loss despite a lower pathogen burden. Our results show that genetic mapping and network modeling can be combined to identify causal pathways underlying chlamydial disease susceptibility.