Polymorphisms in CD14, mannose-binding lectin, and Toll-like receptor-2 are associated with increased prevalence of infection in critically ill adults*

Single nucleotide polymorphisms in the promoter of the gene encoding the lipopolysaccharide receptor CD14 are associated with bacterial diarrhea in US and Canadian travelers to Mexico

BACKGROUND

Under normal conditions, the expression of CD14, which is the principal receptor for bacterial lipopolysaccharide, is down-regulated in the intestinal mucosa but increases in response to inflammatory stimuli. The aim of the present study was to investigate whether fecal CD14 levels increased in response to infection with diarrheagenic Escherichia coli and whether single nucleotide polymorphisms (SNPs) in the CD14 gene were associated with an increased susceptibility to traveler's diarrhea (TD) in US visitors to Mexico.

METHODS

Six SNPs located at the promoter, exon, and untranslated regions of CD14 were typed in a prospective cohort study of 1360 visitors to Mexico at risk for TD. Stools from visitors with TD were studied for enteric pathogens by culture, colony hybridization, and polymerase chain reaction. Fecal soluble CD14 (sCD14) was measured in a subgroup of 203 adults with diarrhea and 66 healthy controls by enzyme-linked immunosorbent assay.

RESULTS

The minor allele frequencies for CD14 SNPs were significantly different among the various racial and ethnic groups studied. Two SNPs in the promoter region of CD14 (-159 C > T; rs2569190 and -4191 C > T; rs5744441) were found to be associated with TD in White visitors. The -159 TT genotype was associated with a higher risk for TD (Relative risk [RR], 1.21; 95% confidence interval [CI], 1.05-1.38; P = .008), whereas individuals with the -4191 TT genotype were protected from infection (RR, 0.82; 95% CI, 0.71-0.92; P = .006). Subjects with TD excreted higher levels of fecal CD14 than did healthy controls (33,480 pg/mL vs 6178 pg/mL; P < .02). Fecal sCD14 levels were higher in stool samples from visitors with TD and the -159 TT genotype than they were in visitors with the CC/CT genotypes (P = .02), and stool samples from subjects with the -4191 CC genotype had higher fecal sCD14 levels than did stool samples from visitors with the CT/TT (P = .005) genotype. In a multivariate analysis with haplotypes constructed with the 6 SNPs studied, subjects with the haplotype containing the -159 C and the -4191 T allele were less likely to acquire TD (P = .015).

CONCLUSIONS

Our study suggests that CD14 levels increase in response to bacterial diarrhea and that polymorphisms in the CD14 gene influence susceptibility to TD. Intestinal CD14 plays an important role in the innate immune response to enteric pathogens.

Genetic polymorphisms in sepsis

The number of genetic polymorphisms shown to play a role in sepsis continues to increase. At the same time, platforms for genetic sequencing and expression analysis are being refined, allowing unprecedented data generation. International databases may soon facilitate synchrony of genotypic and phenotypic data using enormous numbers of septic patients. If this occurs, 2 strategies for investigating polymorphisms in sepsis are likely to gain favor. In the first strategy, sepsis will continue to be viewed as a single entity. High-throughput genetic techniques will be used to evaluate numerous polymorphisms, each with fractional disease responsibility. Nongenetic variables, such as pathogen characteristics, underlying host medical conditions, and type and timing of resuscitation, will be considered cofactors. Using this approach, principal components that predict susceptibility to and outcomes during sepsis are likely to be identified. In the second strategy, sepsis will be divided into subtypes based on the concentration of specific variables. Categories will be based on features like the presence or absence of specific polymorphisms, gram-positive or gram-negative staining of causative organisms, age and comorbid conditions of the host, recent administration of chemotherapeutic agents, and hospital setting (ie, community vs teaching institution). Each category will be used to create homogenous sepsis subgroups for detailed evaluation. This approach will increase the odds of finding single dominant factors responsible for predilection and/or outcome within well-defined groups among those with sepsis. Several elements will be essential for the success of both these strategies. Firstly, databases that are extremely detailed will have to be generated. Secondly, better clinical information technology systems will be needed to facilitate large-scale phenotyping. Thirdly, standardization of protocols will need to take place to ensure uniformity of data sets. If the rapid advances in technology and informatics continue, they may catalyze paradigm shifts with regard to how clinicians address sepsis. Clinicians may change their focus from aggressive uniform treatment strategies to rapid stratification and subcategorization, with subsequent aggressive targeted therapeutic interventions. Advances in technology have the potential to change our primary goal in sepsis from rapid treatment to prevention for those most at risk. The cost savings to the US health care systems from such changes could be substantial.

The impact of caspase-12 on susceptibility to candidemia

Candida is one of the leading causes of sepsis, and an effective host immune response to Candida critically depends on the cytokines IL-1β and IL-18, which need caspase-1 cleavage to become bioactive. Caspase-12 has been suggested to inhibit caspase-1 activation and has been implicated as a susceptibility factor for bacterial sepsis. In populations of African descent, CASPASE-12 is either functional or non-functional. Here, we have assessed the frequencies of both CASPASE-12 alleles in an African-American Candida sepsis patients cohort compared to uninfected patients with similar predisposing factors. African-American Candida sepsis patients (n = 93) and non-infected African-American patients (n = 88) were genotyped for the CASPASE-12 genotype. Serum cytokine concentrations of IL-6, IL-8, and IFNγ were measured in the serum of infected patients. Statistical comparisons were performed in order to assess the effect of the CASPASE-12 genotype on susceptibility to candidemia and on serum cytokine concentrations. Our findings demonstrate that CASPASE-12 does not influence the susceptibility to Candida sepsis, nor has any effect on the serum cytokine concentrations in Candida sepsis patients during the course of infection. Although the functional CASPASE-12 allele has been suggested to increase susceptibility to bacterial sepsis, this could not be confirmed in our larger cohort of fungal sepsis patients.

TIRAP Ser180Leu polymorphism is associated with Behcet's disease

OBJECTIVES

The initiating cause of Behçet's disease (BD) is unknown, but an aberrant response to infection has been suggested. In this study, single nucleotide polymorphisms in Toll-like receptors (TLRs) and associated molecules that have a sentinel function at mucosal surfaces were analysed in patients with BD.

METHODS

TLR expression was determined by immunohistochemistry in buccal mucosal tissue from patients with BD, in tissue from patients with lichen planus (LP) or pyogenic granuloma (PG) as disease controls, or from healthy individuals. Using SSP-PCR we analysed SNP in CD14, TLR2, TLR4 and TIRAP (TIR domain-containing adaptor protein) in patients with BD from different geographical regions.

RESULTS

TLR expression was increased in buccal lesions from patients with BD compared with healthy controls; however, a similar increase was seen in lesion tissue from patients with LP or PG, suggesting that this was a generalized inflammatory response as opposed to a BD-specific response. SNP analysis showed no association between CD14, TLR2 or TLR4 polymorphisms. However, TIRAP 180Leu was significantly associated with BD in UK, but not Middle Eastern, patients.

CONCLUSION

TLR expression showed no difference in tissue from patients with BD compared with either disease or healthy controls. Likewise, SNPs in TLR genes were no different from healthy controls. The association with the increased function variant of TIRAP suggests that encounter with a pathogen at mucosal sites will lead to increased cytokine production and tissue damage with persistence of mucosal lesions.

A nonsynonymous polymorphism of IRAK4 associated with increased prevalence of gram-positive infection and decreased response to toll-like receptor ligands

Mutations in IRAK4 have been associated with recurrent Gram-positive infections in children. Given the central role of IRAK4 in innate immunity signaling, we hypothesized that common genetic variants of IRAK4 may be associated with prevalence of Gram-positive infection in critically ill adults. Haplotype clade tag single nucleotide polymorphisms (SNPs) of the IRAK4 gene were selected and genotyped in a cohort of 1,029 critically ill patients with systemic inflammatory response syndrome (SIRS). We found that a haplotype clade tagged by the A allele of the htSNP G29429A (Ala428Thr) was associated with increased relative risk of Gram-positive infection at admission to ICU (RR = 1.2, p < 0.05). Furthermore, the 29429A allele was associated with decreased lymphoblastoid cell response to CpG (as measured by IL-6 production) (raw values ± 95% CI 40.3 ± 32.3 vs. 85.8 ± 29.4 pg/ml; log-transformed values ± 95% CI 1.13 ± 0.37 vs. 1.55 ± 0.18, p < 0.04). We also found that IRAK4-deficient fibroblasts transfected with an IRAK4 expression plasmid containing the 29429A allele produced less IL-6 in response to lipopolysaccharide (p = 0.07). Our data suggest that the IRAK4 haplotype clade marked by 29429A (428Thr) alters susceptibility to Gram-positive bacteria, by decreasing cellular response to TLR ligands.

Genetic variations in toll-like receptor pathway genes influence asthma and atopy

Innate immunity is a pivotal defence system of higher organisms. Based on a limited number of receptors, it is capable of recognizing pathogens and to initiate immune responses. Major components of these innate immunity pathogen recognition receptors are the toll-like receptors (TLRs), a family of 11 in humans. They are all membrane bound and through dimerization and complex downstream signaling, TLRs elicit a variety of specific and profound effects. In recent years, the role of TLRs signaling was not only investigated in infection and inflammation but also in allergy. Fuelled by the hygiene hypothesis, which suggests that allergies develop because of a change in microbial exposure and associated immune signals early in life, it had been speculated that alterations in TLRs signaling could influence allergy development. Thus, TLR genes, genetic variations of these genes, and their association with asthma and other atopic diseases were investigated in recent years. This review provides an overview of TLR genetics in allergic diseases.

Interleukin-1 receptor-associated kinase 3 gene associates with susceptibility to acute lung injury

Sepsis is the most common cause of acute lung injury (ALI), leading to organ dysfunction and death in critically ill patients. Previous studies associated variants of interleukin-1 receptor-associated kinase genes (IRAKs) with differential immune responses to pathogens and with outcomes during sepsis, and revealed that increased expression levels of the IRAK3 gene were correlated with poor outcomes during sepsis. Here we explored whether common variants of the IRAK3 gene were associated with susceptibility to, and outcomes of, severe sepsis. After our discovery of polymorphism, we genotyped a subset of seven single-nucleotide polymorphisms (SNPs) in 336 population-based control subjects and 214 patients with severe sepsis, collected as part of a prospective study of adults from a Spanish network of intensive care units. Whereas IRAK3 SNPs were not associated with susceptibility to severe sepsis, rs10506481 showed a significant association with the development of ALI among patients with sepsis (P = 0.007). The association remained significant after adjusting for multiple comparisons, population stratification, and clinical variables (odds ratio, 2.50; 95% confidence interval, 1.15-5.47; P = 0.021). By imputation, we revealed three additional SNPs independently associated with ALI (P < 0.01). One of these (rs1732887) predicted the disruption of a putative human-mouse conserved transcription factor binding site, and demonstrated functional effects in vitro (P = 0.017). Despite the need for replication in independent studies, our data suggest that common SNPs in the IRAK3 gene may be determinants of sepsis-induced ALI.

Genetic polymorphisms and posttraumatic complications

Major trauma is the leading cause of death in young adults. Despite advances in prehospital system and treatment in hospital, mortality rates have not improved significantly over the past decades. Victims of severe injuries who survive the initial hours have great risk for additional life-threatening complicaitons, including uncontrollable infection (sepsis) and multiple organ dysfunction syndrome (MODS). Single nucleotide polymorphisms (SNPs) have been shown to affect susceptibility to the course of numerous diseases. Accumulating evidence suggests that genetic backgrounds also play important roles in posttraumatic complications. Genetic polymorphisms may become powerful biomarkers for diagnosis and prognosis of trauma-induced complications. Recent advances in studies on associations between genetic polymorphisms and sepsis or MODS have led to better understanding of posttraumatic complications. Here we summarise recent findings on genetic variations in molecules of the innate immune system and other systems as well as their connection with susceptibility to posttraumatic complications.

Role of polymorphic variants as genetic modulators of infection in neonatal sepsis

This study is a retrospective, case control study involving 535 preterm infants examining the roles of sequence polymorphisms in genes that mediate host immune responses to bacterial infection in newborn infants. A total of 49 single nucleotide polymorphisms (SNPs) in 19 candidate genes including inflammatory cytokines (IL6, IL10, IL1B, and TNF), cytokine receptors (IL1RN), toll-like receptors (TLR2, TLR4, and TLR5), and cell surface receptors (CD14) were genotyped. Subjects were stratified into three groups (sepsis, suspected sepsis, and control). The data were analyzed using a family-based transmission disequilibrium test. We found that birth weight, gestational age, duration of rupture of membranes, and presence of clinical chorioamnionitis were strongly associated with sepsis. Polymorphisms in TLR2 (rs3804099), TLR5 (rs5744105), IL10 (rs1800896), and PLA2G2A (rs1891320) genes were associated with sepsis. Allelic variants in PLA2G2A and TLR2 were associated with Gram-positive infections, whereas IL10 was associated with Gram-negative infections (p < 0.05). We conclude allelic variations in PLA2G2A, TLR2, TLR5, and IL10 may moderate the predisposition to sepsis in preterm infants.

Can immunogenetics illuminate the diverse manifestations of respiratory infections?

Improved technologies for high-throughput genotyping and the establishment of well-defined cohorts prompted hope that polymorphisms would be discovered that define a patients' risk of respiratory disease or aid in diagnosis. Genetic pitfalls encountered in this quest include genotyping errors, ethnic differences and linkage dysequilibrium. Differences in the definition of the disease phenotype also create discrepancies, so immunogenetic testing has not yet reached the clinic. However, associations between a polymorphism and a disease phenotype place the gene or one in linkage dysequilibrium on the path to the disease. Here we review studies of immune-related genes that are illuminating the immunopathogenesis of community-acquired pneumonia and mycobacterial infections.

The chitinase-like proteins breast regression protein-39 and YKL-40 regulate hyperoxia-induced acute lung injury

RATIONALE

Prolonged exposure to 100% O(2) causes hyperoxic acute lung injury (HALI), characterized by alveolar epithelial cell injury and death. We previously demonstrated that the murine chitinase-like protein, breast regression protein (BRP)-39 and its human homolog, YKL-40, inhibit cellular apoptosis. However, the regulation and roles of these molecules in hyperoxia have not been addressed.

OBJECTIVES

We hypothesized that BRP-39 and YKL-40 (also called chitinase-3-like 1) play important roles in the pathogenesis of HALI.

METHODS

We characterized the regulation of BRP-39 during HALI and the responses induced by hyperoxia in wild-type mice, BRP-39-null (-/-) mice, and BRP-39(-/-) mice in which YKL-40 was overexpressed in respiratory epithelium. We also compared the levels of tracheal aspirate YKL-40 in premature newborns with respiratory failure.

MEASUREMENTS AND MAIN RESULTS

These studies demonstrate that hyperoxia inhibits BRP-39 in vivo in the murine lung and in vitro in epithelial cells. They also demonstrate that BRP-39(-/-) mice have exaggerated permeability, protein leak, oxidation, inflammatory, chemokine, and epithelial apoptosis responses, and experience premature death in 100% O(2). Lastly, they demonstrate that YKL-40 ameliorates HALI, prolongs survival in 100% O(2), and rescues the exaggerated injury response in BRP-39(-/-) animals. In accord with these findings, the levels of tracheal aspirate YKL-40 were lower in premature infants treated with hyperoxia for respiratory failure who subsequently experienced bronchopulmonary dysplasia or death compared with those that did not experience these complications.

CONCLUSIONS

These studies demonstrate that hyperoxia inhibits BRP-39/YKL-40, and that BRP-39 and YKL-40 are critical regulators of oxidant injury, inflammation, and epithelial apoptosis in the murine and human lung.

Genetic risk of acute pulmonary infections and sepsis

The focus of this review is the genetic influence on pneumonia and sepsis. A large number of polymorphisms in a diverse collection of genes have been identified as potential candidates to explain the genetic variability in susceptibility to acute pulmonary infection and its adverse outcomes. Unfortunately, apart from polymorphisms in mannose-binding lectin, CD14 and the IgG2 receptor, there is little consensus on which polymorphisms are truly important. As well as discussing some of the major published findings, this review will focus on the reasons for failure to make more progress. We will also address the issues for future research, particularly the need to address the limitations of past studies, including the grouping of patients with different pathogens, as the relationship between genotype and phenotype may be highly pathogen dependent. Finally, our approach to reporting genetic studies needs to change to minimize the number of publications of spurious findings.

Genomic polymorphisms within alpha 7 nicotinic acetylcholine receptor and severe sepsis in Chinese Han population

Alpha 7 nicotinic acetylcholine receptor, a kind of ligand-gated ion channel mainly expressed in macrophages, plays a crucial role in improving survival in sepsis via suppressing proinflammatory cytokines. The predisposition of genomic polymorphisms within alpha 7 nicotinic acetylcholine receptor gene (CHRNA7) to sepsis has not been investigated. The current association study was performed to analyse six common genetic variations within 5'-upstream region of CHRNA7 gene in 229 patients with severe sepsis and 267 controls. Neither allelic frequencies nor genotype distributions were significantly different between patients and controls, as well as between surviving and nonsurviving patients. The frequencies of estimated haplotypes were also comparable between above defined groups. The present study suggests that genomic polymorphisms in the 5'-upstream region of CHRNA7 gene may not be a major risk factor for severe sepsis in Chinese Han population.

Restriction Site Tiling Analysis: accurate discovery and quantitative genotyping of genome-wide polymorphisms using nucleotide arrays

A method for the simultaneous identification of polymorphic loci and the quantitative genotyping of thousands of loci in individuals is presented.

High-throughput genotype data can be used to identify genes important for local adaptation in wild populations, phenotypes in lab stocks, or disease-related traits in human medicine. Here we advance microarray-based genotyping for population genomics with Restriction Site Tiling Analysis. The approach simultaneously discovers polymorphisms and provides quantitative genotype data at 10,000s of loci. It is highly accurate and free from ascertainment bias. We apply the approach to uncover genomic differentiation in the purple sea urchin.

Ethical considerations in the collection of genetic data from critically ill patients: what do published studies reveal about potential directions for empirical ethics research?

Critical illness trials involving genetic data collection are increasingly commonplace and pose challenges not encountered in less acute settings, related in part to the precipitous, severe and incapacitating nature of the diseases involved. We performed a systematic literature review to understand the nature of such studies conducted to date, and to consider, from an ethical perspective, potential barriers to future investigations. We identified 79 trials enrolling 24 499 subjects. Median (interquartile range) number of participants per study was 263 (116.75-430.75). Of these individuals, 16 269 (66.4%) were Caucasian, 1327 (5.4%) were African American, 1707 (7.0%) were Asian Pacific Islanders and 139 (0.6%) were Latino. For 5020 participants (20.5%), ethnicity was not reported. Forty-eight studies (60.8%) recruited subjects from single centers and all studies examined a relatively small number of genetic markers. Technological advances have rendered it feasible to conduct clinical studies using high-density genome-wide scanning. It will be necessary for future critical illness trials using these approaches to be of greater scope and complexity than those so far reported. Empirical research into issues related to greater ethnic inclusivity, accuracy of substituted judgment and specimen stewardship may be essential for enabling the conduct of such trials.

Polymorphisms of genes encoding tumor necrosis factor-alpha, interleukin-10, cluster of differentiation-14 and interleukin-1ra in critically ill patients

PURPOSE

The aim of the study was to determine whether distributions of tumor necrosis factor (TNF)-α(308), interleukin (IL)-10(1082), CD14(159), and IL-1ra gene intron 2 genotypes in critically ill patients are associated with outcome, underlying cause of sepsis, and type of microorganism.

MATERIALS AND METHODS

Blood samples from 106 critically ill white patients were genotyped by method based on polymerase chain reaction for TNF-α(308), IL-10(1082), CD14(159), and IL-1ra gene intron 2.

RESULTS

All patients with TNF-α(308)AA genotype survived; relative risk (RR) of death in patients with AG was 3.250 and with GG, 1.923 (P < .01). In patients with Gram-positive sepsis, IL-10(1082)AA and then AG genotypes were the most frequent ones (odds ratio [OR], 18.67 and 7.20, respectively; P < .01). When comparing IL-10(1082)AA with AG, RR of pancreatitis was 1.80 and OR was 3.40. When AA and GG were compared, RR was 7.33 and OR was 20.00. In patients with GG, RR of peritonitis was 4.07 and OR was 5.88 (P < .01). In patients with Gram-positive sepsis, CD14(159)CT was the most frequent one with OR of 5.25. Distribution of 6 IL-1ra gene intron 2 genotypes showed no significant association.

CONCLUSIONS

Distribution of TNF-α(308) genotypes is associated with outcome, IL-10(1082) with type of microorganism and underlying cause of sepsis, and CD14(159) with type of microorganism.

Toll-like receptors and B-cell receptors synergize to induce immunoglobulin class-switch DNA recombination: relevance to microbial antibody responses

Differentiation of naïve B cells, including immunoglobulin class-switch DNA recombination, is critical for the immune response and depends on the extensive integration of signals from the B-cell receptor (BCR), tumor necrosis factor (TNF) family members, Toll-like receptors (TLRs), and cytokine receptors. TLRs and BCR synergize to induce class-switch DNA recombination in T cell-dependent and T cell-independent antibody responses to microbial pathogens. BCR triggering together with simultaneous endosomal TLR engagement leads to enhanced B-cell differentiation and antibody responses. Te requirement of both BCR and TLR engagement would ensure appropriate antigen-specific activation in an infection. Co-stimulation of TLRs and BCR likely plays a significant role in anti-microbial antibody responses to contain pathogen loads until the T cell-dependent antibody responses peak. Furthermore, the temporal sequence of different signals is also critical for optimal B cell responses, as exemplified by the activation of B cells by initial TLR engagement, leading to the up-regulation of co-stimulatory CD80 and MCH-II receptors, which result in more efficient interactions with T cells, thereby enhancing the germinal center reaction and antibody affinity maturation. Overall, BCR and TLR stimulation and the integration with signals from the pathogen or immune cells and their products determine the ensuing B-cell antibody response.

Genotypes coding for low serum levels of mannose-binding lectin are underrepresented among individuals suffering from noninfectious systemic inflammatory response syndrome

Gene polymorphisms, giving rise to low serum levels of mannose-binding lectin (MBL) or MBL-associated protease 2 (MASP2), have been associated with an increased risk of infections. The objective of this study was to assess the outcome of intensive care unit (ICU) patients with systemic inflammatory response syndrome (SIRS) regarding the existence of functionally relevant MBL2 and MASP2 gene polymorphisms. The study included 243 ICU patients with SIRS admitted to our hospital, as well as 104 healthy control subjects. MBL2 and MASP2 single nucleotide polymorphisms were genotyped using a sequence-based typing technique. No differences were observed regarding the frequencies of low-MBL genotypes (O/O and XA/O) and MASP2 polymorphisms between patients with SIRS and healthy controls. Interestingly, ICU patients with a noninfectious SIRS had a lower frequency for low-MBL genotypes and a higher frequency for high-MBL genotypes (A/A and A/XA) than either ICU patients with an infectious SIRS or healthy controls. The existence of low- or /high-MBL genotypes or a MASP2 polymorphism had no impact on the mortality rates of the included patients. The presence of high-MBL-producing genotypes in patients with a noninfectious insult is a risk factor for SIRS and ICU admission.

Pattern recognition receptor-dependent mechanisms of acute lung injury

Acute lung injury (ALI) that clinically manifests as acute respiratory distress syndrome is caused by an uncontrolled systemic inflammatory response resulting from clinical events including sepsis, major surgery and trauma. Innate immunity activation plays a central role in the development of ALI. Innate immunity is activated through families of related pattern recognition receptors (PRRs), which recognize conserved microbial motifs or pathogen-associated molecular patterns (PAMPs). Toll-like receptors were the first major family of PRRs discovered in mammals. Recently, NACHT-leucine-rich repeat (LRR) receptors and retinoic acid-inducible gene-like receptors have been added to the list. It is now understood that in addition to recognizing infectious stimuli, both Toll-like receptors and NACHT-LRR receptors can also respond to endogenous molecules released in response to stress, trauma and cell damage. These molecules have been termed damage-associated molecular patterns (DAMPs). It has been clinically observed for a long time that infectious and noninfectious insults initiate inflammation, so confirmation of overlapping receptor-signal pathways of activation between PAMPs and DAMPs is no surprise. This review provides an overview of the PRR-dependent mechanisms of ALI and clinical implication. Modification of PRR pathways is likely to be a logical therapeutic target for ALI/acute respiratory distress syndrome.

CD14 C-159T and toll-like receptor 4 Asp299Gly polymorphisms in surviving meningococcal disease patients

Background

Carriage of Neisseria meningitidis occurs approximately in 10% of the population, onset of invasive meningococcal disease (IMD) cannot be predicted and differs between ages. It remains unclear, which host factors determine invasion of the bloodstream by the bacteria. Innate immunity has a very important role in the first recognition of invading pathogens. The functional single nucleotide polymorphisms (SNPs) CD14 C-159T and toll-like receptor 4 (TLR4) Asp299Gly have been associated with the risk of gram-negative infections. However, their role in development of IMD still remains unclear. Our aim was to investigate the influence of CD14 C-159T and TLR4 Asp299Gly polymorphisms on the risk of IMD.

Methodology/Principal Findings

It was a retrospective case control study. Surviving Austrian meningococcal disease patients were enrolled by sending buccal swabs for DNA analysis. 185 cases with a proven meningococcal infection and 770 healthy controls were enrolled. In surviving meningococcal disease patients DNA analysis of CD14 C-159T and TLR 4 Asp299Gly polymorphisms was performed, as they are part of the innate immune response to bacterial determinants. CD14 C-159T and TLR4 Asp299Gly SNPs were not significantly associated with the presence of IMD when compared to healthy controls. The odds ratio for CD14 C-159T SNP was 1.14 (95% confidence interval (CI) 0.91–1.43; p = 0.266). In TLR4 Asp 299 Gly SNP the odds ratio was 0.78 (CI 0.47–1.43; p = 0.359).

Conclusion/Significance

We could not observe a significant influence of CD14 C-159T and TLR4 Asp299Gly polymorphisms on the risk of developing IMD in surviving meningococcal disease patients. To our knowledge, this is the first study investigating the influence of the CD14 C-159T SNP on the susceptibility to IMD.

Polymorphism in the Promoter Region of the CD14 Gene and Susceptibility to Brucellosis

A single-nucleotide polymorphism in the promoter region of the CD14 gene at position 159 has been implicated in susceptibility to infectious diseases. We sought to determine the association between CD14 C-159 T functional promoter polymorphism and brucellosis in Western Iranian population where the disease is endemic. The CD14 genotype was determined in 228 patients with brucellosis from a rural area and 129 healthy volunteers from the same area. The prevalence of genotype TT was significantly higher in the patients while the controls showed higher prevalence of genotype CC (34.5% vs 15.5%, 15.4% vs 25.6%, P = 0.009). Multiple logistic regression analysis after adjustment for gender demonstrated that the patients who were homozygous for allele T of promoter of CD14 gene had a significantly higher risk for developing brucellosis with odds ratio of 3.03 (95% CI, 5.2, 1.75 P = 0.0004). The existence of homozygous genotype of allele T of CD14 was an independent determinant for occurrence of arthritis among the patients with brucellosis (odds ratio of 3.92 (95% CI, 2.93, 5.88, P = 0.001).Our findings provide suggestive evidence of association of the CD14 gene polymorphism with susceptibility to development of brucellosis in Iranian populations.

Bench-to-bedside review: Association of genetic variation with sepsis

Susceptibility and response to infectious disease is, in part, heritable. Initial attempts to identify the causal genetic polymorphisms have not been entirely successful because of the complexity of the genetic, epigenetic, and environmental factors that influence susceptibility and response to infectious disease and because of flaws in study design. Potential associations between clinical outcome from sepsis and many inflammatory cytokine gene polymorphisms, innate immunity pathway gene polymorphisms, and coagulation cascade polymorphisms have been observed. Confirmation in large, well conducted, multicenter studies is required to confirm current findings and to make them clinically applicable. Unbiased investigation of all genes in the human genome is an emerging approach. New, economical, high-throughput technologies may make this possible. It is now feasible to genotype thousands of tag single nucleotide polymorphisms across the genome in thousands of patients, thus addressing the issues of small sample size and bias in selecting candidate polymorphisms and genes for genetic association studies. By performing genome-wide association studies, genome-wide scans of nonsynonymous single nucleotide polymorphisms, and testing for differential allelic expression and copy number polymorphisms, we may yet be able to tease out the complex influence of genetic variation on susceptibility and response to infectious disease.

The interaction of mannose binding lectin (MBL) with mannose containing glycopeptides and the resultant potential impact on invasive fungal infection

Mannnose-binding lectin (MBL) binds oligosaccharides on the surface of microorganisms to form complexes that activate the complement cascade and facilitate phagocytosis. Teicoplanin and dalbavancin glycopeptide antibiotics possess N-acetyl glucosamine and mannose oligosaccharides that may bind MBL. Pharmaceuticals capable of binding to MBL may decrease clearance of significant pathogens such as yeast. An invasive candidemia murine model was utilized to evaluate differences in survival between mannose- and teicoplanin-treated groups compared to a control group administered normal saline. Three groups of BALB/c mice were injected with Candida albicans ATCC 44858 (1.4 x 10(6) CFU). Pharmaceutical agents were administered 2 h pre-infection and 8 h post-infection. In vivo cumulative survival at 52 h revealed 10%, 30% and 90% survival rates for mice administered mannose, teicoplanin, and saline, respectively. There was 0% survival for mice given mannose or teicoplanin at 56 h, compared with 70% for the normal saline treated mice at the same time point (P < 0.05). This in vivo study shows 'accelerated progression of infection' for Candida-inoculated mice exposed to mannose or teicoplanin compared to those given normal saline. Further, protein polyacrylamide gel electrophoresis studies suggested a potential MBL-drug interaction which may attenuate complement activation, opsonization and phagocytosis.

Recent advances in genetic predisposition to clinical acute lung injury

It has been well established that acute lung injury (ALI), and the more severe presentation of acute respiratory distress syndrome (ARDS), constitute complex traits characterized by a multigenic and multifactorial etiology. Identification and validation of genetic variants contributing to disease susceptibility and severity has been hampered by the profound heterogeneity of the clinical phenotype and the role of environmental factors, which includes treatment, on outcome. The critical nature of ALI and ARDS, compounded by the impact of phenotypic heterogeneity, has rendered the amassing of sufficiently powered studies especially challenging. Nevertheless, progress has been made in the identification of genetic variants in select candidate genes, which has enhanced our understanding of the specific pathways involved in disease manifestation. Identification of novel candidate genes for which genetic association studies have confirmed a role in disease has been greatly aided by the powerful tool of high-throughput expression profiling. This article will review these studies to date, summarizing candidate genes associated with ALI and ARDS, acknowledging those that have been replicated in independent populations, with a special focus on the specific pathways for which candidate genes identified so far can be clustered.

Influence of the Toll-like receptor 9 1635A/G polymorphism on the CD4 count, HIV viral load, and clinical progression

OBJECTIVE

: To analyze the influence of single-nucleotide polymorphisms (SNPs) in TLR2 (1892A/C and 2258G/A), TLR4 (896A/G and 1196C/T), and TLR9 (1635A/G) genes on CD4 count, HIV viral load, and clinical progression in a cohort of naive HIV-infected patients.

METHODS

: TLR2, TLR4, and TLR9 SNPs were analyzed in 369 naive HIV-infected patients by real-time polymerase chain reaction and melting curve technology. TLR2 1892C/A and TLR9 1635A/G SNPs were also analyzed in a non-HIV-infected population. Multivariate multiple regression analysis and Cox regression analyses were performed to assess the potential association between the SNPs and the end points.

RESULTS

: TLR2 and TLR4 SNPs were not associated with the end points of the study. Regarding TLR9 1635A/G SNP, patients with the AA genotype showed statistically lower CD4 count (P = 0.003) and higher HIV viral load (P = 0.0018) compared with AG+GG genotypes at cohort entry. The multivariate analysis showed a significant association between the 1635AA genotype and both end points. Cox regression analysis showed that HIV clinical progression to clinical stage C and death due to AIDS-related events under antiretroviral therapy was earlier in patients with the 1635AA genotype (P = 0.035, P = 0.017, respectively).

CONCLUSIONS

: TLR9 1635A/G SNP might have a role in HIV clinical disease progression.

Genetic influence on bloodstream infections and sepsis

Bloodstream infections (BSIs) are a major burden in health care today, associated with considerable morbidity, mortality and costs. They are either caused by direct influx of pathogens via devices into the blood (primary BSI) or by bacterial spillover from infected distant organs (secondary BSI). The recognition of invading microbes by sensing of conserved molecular patterns is pivotal for the host in staging an adequate immune response to eradicate the pathogen. Moreover, a balanced immune response is crucial to avoid over inflammation followed by additional damage to the host. This complex host response pattern is controlled by soluble proteins and cellular receptors, which have recently been found to contain substantial individual genetic variations. Single nucleotide polymorphisms have been shown to affect susceptibility to and the course of numerous diseases. A large number of genes and their products are involved in the host reaction to BSIs, and genetic variation in these molecules alters the frequency and course of these events. Here we summarise recent findings on genetic variations in molecules of the innate immune system and other systems as well as their connection with susceptibility to BSIs and sepsis and the way the host stages a beneficial response to infection.

Low serum mannose-binding lectin level increases the risk of death due to pneumococcal infection

BACKGROUND

Previous studies have shown associations between low mannose-binding lectin (MBL) level or variant MBL2 genotype and sepsis susceptibility. However, MBL deficiency has not been rigorously defined, and associations with sepsis outcomes have not been subjected to multivariable analysis.

METHODS

We reanalyzed MBL results in a large cohort with use of individual data from 4 studies involving a total of 1642 healthy control subjects and systematically defined a reliable deficiency cutoff. Subsequently, data were reassessed to extend previous MBL and sepsis associations, with adjustment for known outcome predictors. We reanalyzed individual data from 675 patients from 5 adult studies and 1 pediatric study of MBL and severe bacterial infection.

RESULTS

XA/O and O/O MBL2 genotypes had the lowest median MBL concentrations. Receiver operating characteristic analysis revealed that an MBL cutoff value of 0.5 microg/mL was a reliable predictor of low-producing MBL2 genotypes (sensitivity, 82%; specificity, 82%; negative predictive value, 98%). MBL deficiency was associated with increased likelihood of death among patients with severe bacterial infection (odds ratio, 2.11; 95% confidence interval, 1.30-3.43). In intensive care unit-based studies, there was a trend toward increased risk of death among MBL-deficient patients (odds ratio, 1.58; 95% confidence interval, 0.90-2.77) after adjustment for Acute Physiology and Chronic Health Enquiry II score. The risk of death was increased among MBL-deficient patients with Streptococcus pneumoniae infection (odds ratio, 5.62; 95% confidence interval, 1.27-24.92) after adjustment for bacteremia, comorbidities, and age.

CONCLUSIONS

We defined a serum level for MBL deficiency that can be used with confidence in future studies of MBL disease associations. The risk of death was increased among MBL-deficient patients with severe pneumococcal infection, highlighting the pathogenic significance of this innate immune defence protein.

Interleukin-6 polymorphisms are associated with pathogenic bacteria in subjects with periodontitis

BACKGROUND

Growing evidence suggests that individual genetic susceptibility may influence the host's response to infections. Previously, we showed that a common variation in the interleukin (IL)-6 gene was associated with increased odds of detection of common periodontal pathogens from individuals with aggressive periodontitis. The aim of this study was to investigate the association between IL-6 polymorphisms and periodontopathogenic bacteria in a larger, ethnically mixed population of subjects with periodontitis.

METHODS

Genomic DNA was extracted from 107 subjects diagnosed with severe forms of periodontitis to study a cluster of polymorphisms in inflammatory genes, including IL-6. The presence of Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), Porphyromonas gingivalis, and Tannerella forsythia (previously T. forsythensis) in their subgingival biofilm was determined by polymerase chain reaction analysis. Serum IL-6 and C-reactive protein (CRP) concentrations were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Multiple logistic regression analysis revealed that the IL-6 -6106 polymorphism was associated with the detection of A. actinomycetemcomitans (P = 0.009; odds ratio [OR] = 3.5; 95% confidence interval [CI]: 1.38 to 9.16) and the concomitant detection of A. actinomycetemcomitans and P. gingivalis (P = 0.015; OR = 3.6; 95% CI: 1.28 to 10.04). The IL-6 -174 polymorphism was associated with increased odds of the concomitant detection of A. actinomycetemcomitans and P. gingivalis (P = 0.042; OR = 2.8; 95% CI: 1.04 to 7.75). Haplotype analysis of all five IL-6 polymorphisms confirmed an association with the detection of A. actinomycetemcomitans (P = 0.046). The IL-6 -6106 polymorphism was also associated with CRP serum levels at multivariate analysis (P = 0.024).

CONCLUSIONS

These findings confirm the hypothesis that complex interactions between the microbiota and host genome are at the basis of susceptibility to periodontitis. Periodontal disease may represent a useful model to study the pathways and mechanisms of host-pathogen interactions in inflammatory diseases.

Toll-like receptor 1 polymorphisms affect innate immune responses and outcomes in sepsis

RATIONALE

Polymorphisms affecting Toll-like receptor (TLR)-mediated responses could predispose to excessive inflammation during an infection and contribute to an increased risk for poor outcomes in patients with sepsis.

OBJECTIVES

To identify hypermorphic polymorphisms causing elevated TLR-mediated innate immune cytokine and chemokine responses and to test whether these polymorphisms are associated with increased susceptibility to death, organ dysfunction, and infections in patients with sepsis.

METHODS

We screened single-nucleotide polymorphisms (SNPs) in 43 TLR-related genes to identify variants affecting TLR-mediated inflammatory responses in blood from healthy volunteers ex vivo. The SNP associated most strongly with hypermorphic responses was tested for associations with death, organ dysfunction, and type of infection in two studies: a nested case-control study in a cohort of intensive care unit patients with sepsis, and a case-control study using patients with sepsis, patients with sepsis-related acute lung injury, and healthy control subjects.

MEASUREMENTS AND MAIN RESULTS

The SNP demonstrating the most hypermorphic effect was the G allele of TLR1(-7202A/G) (rs5743551), which associated with elevated TLR1-mediated cytokine production (P < 2 x 10(-20)). TLR1(-7202G) marked a coding SNP that causes higher TLR1-induced NF-kappaB activation and higher cell surface TLR1 expression. In the cohort of patients with sepsis TLR1(-7202G) predicted worse organ dysfunction and death (odds ratio, 1.82; 95% confidence interval, 1.07-3.09). In the case-control study TLR1(-7202G) was associated with sepsis-related acute lung injury (odds ratio, 3.40; 95% confidence interval, 1.59-7.27). TLR1(-7202G) also associated with a higher prevalence of gram-positive cultures in both clinical studies.

CONCLUSIONS

Hypermorphic genetic variation in TLR1 is associated with increased susceptibility to organ dysfunction, death, and gram-positive infection in sepsis.

Mannose-binding lectin and mannose-binding lectin-associated serine protease 2 in susceptibility, severity, and outcome of pneumonia in adults

BACKGROUND

Community-acquired pneumonia (CAP) is the leading cause of death from infection in developed countries. Mannose-binding lectin (MBL) and MBL-associated serine protease 2 (MASP-2) deficiencies are common primary immunodeficiencies the clinical penetrance of which remains controversial. MBL is a serum lectin that mediates phagocytosis and activates the lectin pathway of complement involving MASP-2.

OBJECTIVE

We sought to evaluate the significance of MBL deficiency (O/O genotypes) and insufficiency (O/O plus XA/O genotypes), as well as MASP-2 deficiency (D105G mutation), in the susceptibility to and severity and outcome of CAP in adults.

METHODS

MBL and MASP-2 serum levels, as well as lectin pathway activity with regard to MBL2 and MASP2 genotypes, were measured in healthy control subjects. For susceptibility, 848 patients with CAP, 1447 healthy control subjects, and a control group of 519 patients without relevant infectious diseases were studied in a case-control study. Severity and outcome were evaluated in a prospective study of the 848 patients.

RESULTS

We found similar frequencies of MBL2 and MASP2 alleles and genotypes among patients and control subjects. However, in a multivariate analysis MBL insufficiency was associated with the development of the most severe forms of sepsis (P = .007), acute respiratory failure (P = .009), multiorgan dysfunction syndrome (P = .036), intensive care unit admission (P = .020), and death (P = .003).

CONCLUSION

Our large study suggests that MBL plays a redundant role in human defenses against primary infection, at least in adults with CAP, and provides, for the first time, evidence that MBL insufficiency predisposes to higher severity and fatal outcome in patients with CAP, irrespective of the causal microorganisms.

Immunomodulating Activity of Agaricus brasiliensis KA21 in Mice and in Human Volunteers

We performed studies on murine models and human volunteers to examine the immunoenhancing effects of the naturally outdoor-cultivated fruit body of Agaricus brasiliensis KA21 (i.e. Agaricus blazei). Antitumor, leukocyte-enhancing, hepatopathy-alleviating and endotoxin shock-alleviating effects were found in mice. In the human study, percentage body fat, percentage visceral fat, blood cholesterol level and blood glucose level were decreased, and natural killer cell activity was increased. Taken together, the results strongly suggest that the A. brasiliensis fruit body is useful as a health-promoting food.

Role of Toll-like receptors in the development of sepsis

The outcome of sepsis and septic shock has not significantly improved in recent decades despite the development of numerous drugs and supportive care therapies. To reduce sepsis-related mortality, a better understanding of molecular mechanism(s) associated with the development of sepsis and sepsis-related organ injury is essential. There is increasing evidence that Toll-like receptors (TLRs) play a key role in the mediation of systemic responses to invading pathogens during sepsis. However, the role of TLRs in the development of sepsis and in sepsis-related organ injury remains debatable. In this review, we focus on the biological significance of TLRs during sepsis. Medline was searched for pertinent publications relating to TLRs, with emphasis on their clinical and pathophysiological importance in sepsis. In addition, a summary of the authors' own experimental data from this field was set in the context of current knowledge regarding TLRs. In both animal models and human sepsis, TLRs are highly expressed on monocytes/macrophages, and this TLR expression may not simply be a ligand-specific response in such an environment. The fact that TLR signaling enables TLRs to recognize harmful mediators induced by invading pathogens may be associated with a positive feedback loop for the inflammatory response among different cell populations. This mechanism(s) may contribute to the organ dysfunction and mortality that occurs in sepsis. A better understanding of TLR biology may unveil novel therapeutic approaches for sepsis.

159C>T CD14 genotype--functional effects on innate immune responses in term neonates

Given the susceptibility of newborns to infection and the potential harm of overwhelming proinflammatory immune responses, the impact of genetic variation in innate immune molecules is of increasing interest for risk stratification and prevention. We studied the functional relevance of the 159C>T CD14 single nucleotide polymorphism in cord blood samples of n=135 healthy term neonates by investigation of sCD14, interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-alpha concentrations in whole-blood culture supernatants and intracellular assessment of IL-1beta, IL-6, and TNF-alpha expression by flow cytometry. The 159C>T CD14 genotype frequencies were n=42 (0.31) for homozygous CD14-159 CC, n=69 (0.51) for heterozygous CD14-159 CT, and n=24 (0.18) for homozygous CD14-159 TT. No genotype-associated differences were noted for ex vivo baseline expression of sCD14, IL-6, IL-10, and TNF-alpha. After in vitro stimulation of cord blood cultures with lipopolysaccharide, carriers of the CD14-159 T allele were determined to have higher levels of sCD14 compared with carriers of the CD14-159 C allele (p=0.04) and increased concentrations of IL-6 (p=0.009) in culture supernatants (one-way analysis of variance). The 159C>T CD14 polymorphism is associated with soluble CD14 expression and cytokine expression, which might influence the balance of pro- and anti-inflammatory immune responses in healthy term neonates. Further studies are needed to delineate whether the 159C>T CD14 genotype is a risk factor for severity of neonatal infection in the clinical setting and a potential target for prevention strategies.

Host defense genes in asthma and sepsis and the role of the environment

PURPOSE OF REVIEW

There is growing evidence that innate immunity genes contribute to asthma pathogenesis. At the core of the innate immune response are ubiquitous, soluble fragments of bacterial lipopolysaccharide or endotoxin, and chronic exposure to domestic endotoxin has been shown to influence asthma severity. Asthmatic and atopic individuals are more sensitive to endotoxin than nonallergic individuals, suggesting a role for genetics in the innate immunity response, and the potential for gene-environment interactions. Variants in genes associated with classic innate immunity-related disorders, such as sepsis, may be unique candidates for asthma susceptibility.

RECENT FINDINGS

Candidate genes for asthma and allergic diseases co-associated with sepsis including innate immunity receptors and related molecules (CD14, TLR4 and AOAH) and novel genes such as MYLK provide good examples of pleitropic effects of innate immunity genes, where variants conferring risk to specific traits (i.e. sepsis) under one set of genetic and environmental circumstances confer a reduced risk in a different (but possibly related) clinical outcome (i.e. allergic asthma), and support the 'common variant/multiple disease' hypothesis.

SUMMARY

Collectively, these observations suggest a greater role for the innate immunity response in allergic asthma than previously assumed, and implicate host defense genes in disease pathology.

Toll-like receptor polymorphisms and susceptibility to human disease

Although several lines of evidence suggest that variation in human inflammation is genetically controlled, the genes which regulate these responses are largely unknown. TLRs (Toll-like receptors) mediate recognition of microbes, regulate activation of the innate immune response and influence the formation of adaptive immunity. Cellular and molecular studies over the past several years have identified a number of common TLR polymorphisms that modify the cellular immune response and production of cytokines in vitro. In addition, human genetic studies suggest that some of these polymorphisms are associated with susceptibility to a spectrum of diseases. In this review, we summarize studies of common TLR polymorphisms and how this work is beginning to illuminate the influence of human variation on inflammation and disease susceptibility.

The Genetics of Sepsis: The Promise, the Progress and the Pitfalls

Physicians are used to taking a family history of cardiovascular disease because of the known significant hereditary risk; yet the familial risk of dying from infection is even greater than that for atherosclerotic disease (Sorensen et al. 1988). There is certainly no doubt that genetic differences impact on the risk of developing or dying from infection. Obvious but rare examples include selective immunoglobulin deficiencies, complement deficiencies, and neutrophil function abnormalities. Genetic factors may also be protective, such as with sickle cell trait and malaria or mutations conferring resistance to human immunodeficiency virus infection.

Much more subtle differences in immune responses are now being described, usually as the result of one or more single nucleotide polymorphisms (SNP) in a gene. Rather than causing the failure of production of a protein or the production of a nonfunctional protein, SNPs are usually associated with changes in the rate of transcription, producing a much less severe phenotype than the classical examples of genetic defects mentioned above. It is now being appreciated that for many complex diseases, such as sepsis, the ultimate phenotype is the result of the interaction of genetic differences across many loci, not the dominant effect of a few key mutations.

As seen in Fig. 3.1, since the mid 1990s, an increasing body of literature has focused on the role that gene polymorphisms in key inflammatory genes play in sepsis. Indeed, with advances in knowledge of the human genome, greater understanding of the inflammatory response, and the development of high throughput genotyping technologies, so many genetic associations have been described that discussion of each one is well beyond the scope of this chapter. I will however summarize those findings that have been reported by multiple groups, as well as give an overview of the major groups of genes that have been implicated in genetic predisposition to sepsis and its adverse outcomes.

M protein from Streptococcus pyogenes induces tissue factor expression and pro-coagulant activity in human monocytes

Invasive infections caused by the important pathogen Streptococcus pyogenes are often associated with disturbed blood coagulation in the human host, and may in severe cases develop into the life-threatening condition disseminated intravascular coagulation. In this study, the addition of M1 protein to human blood or purified peripheral blood mononuclear cells led to a dose-dependent increase of pro-coagulant activity, which was mediated by an upregulation of tissue factor on monocytes. Analysis of the resulting clots by transmission electron microscopy revealed that the cells were covered with a fibrin network that seemed to originate from the cell surface. Taken together, the results imply an important role for M proteins in the induction of haemostatic disorders in invasive streptococcal infectious diseases.

The genetic predisposition to adverse outcome after trauma

Technological advances and shorter rescue times have allowed early and effective resuscitation after trauma and brought attention to the host response to injury. Trauma patients are at risk of progressive organ dysfunction from what appears to be an uncontrolled immune response. The availability of improved techniques of molecular diagnosis has allowed investigation of the role of genetic variations in the inflammatory response to post-traumatic complications and particularly to sepsis.

This review examines the current evidence for the genetic predisposition to adverse outcome after trauma. While there is evidence supporting the involvement of different polymorphic variants of genes in determining the post-traumatic course and the development of complications, larger-scale studies are needed to improve the understanding of how genetic variability influences the responses to post-traumatic complications and pharmacotherapy.

Innate immunogenetics: a tool for exploring new frontiers of host defence

The discovery of innate immune genes, such as those encoding Toll-like receptors (TLRs), nucleotide-binding oligomerisation domain-like receptors (NLRs), and related signal-transducing molecules, has led to a substantial improvement of our understanding of innate immunity. Recent immunogenetic studies have associated polymorphisms of the genes encoding TLRs, NLRs, and key signal-transducing molecules, such as interleukin-1 receptor-associated kinase 4 (IRAK4), with increased susceptibility to, or outcome of, infectious diseases. With the availability of high-throughput genotyping techniques, it is becoming increasingly evident that analyses of genetic polymorphisms of innate immune genes will further improve our knowledge of the host antimicrobial defence response and help in identifying individuals who are at increased risk of life-threatening infections. This is likely to open new perspectives for the development of diagnostic, predictive, and preventive management strategies to combat infectious diseases.