SNPing away at innate immunity

Association between Toll-like receptor 2 (TLR2) polymorphisms and asymptomatic bancroftian filariasis

Lymphatic filariasis is mainly caused by the filarial nematodes Wuchereria bancrofti and Brugia malayi. Wolbachia, intracellular symbiotic bacteria in filarial parasite, is known to induce immune response predominantly through Toll-like receptor 2 (TLR2). This study was performed to investigate the association between polymorphisms of the TLR2 gene and susceptibility to asymptomatic bancroftian filariasis. A total of 142 unrelated asymptomatic bancroftian filariasis patients and 151 endemic normal controls in Tak province, Thailand were recruited into this study. The -196 to -173 deletion (del) polymorphism in the 5' untranslated region was investigated by allele-specific polymerase chain reaction. Two single nucleotide polymorphisms, +597 T>C and +1350 T>C, in exon 3 were identified by polymerase chain reaction-restriction fragment length polymorphism analysis. Furthermore, we analyzed the functional difference between the TLR2 -196 to -173 del and wild-type (wt) alleles using the luciferase reporter assay. All three polymorphisms were associated with a higher risk of asymptomatic bancroftian filariasis and were in strong linkage disequilibrium with each other. The TLR2 haplotype -196 to -173del/+597C/+1350C was strongly associated with an increased risk of asymptomatic bancroftian filariasis. The TLR2 -196 to -173 del allele had a significantly lower transcriptional activity than wt allele. The results of our study indicate that TLR2 -196 to -173 del, +597 T>C and +1350 T>C polymorphisms are associated with asymptomatic bancroftian filariasis in Thailand. Our functional study also supports this finding with respect to differential TLR2 gene expression by -196 to -173 del polymorphism.

Myeloperoxidase promoter polymorphism -463G is associated with more severe clinical expression of cystic fibrosis pulmonary disease

The severity of cystic fibrosis (CF) pulmonary disease is not directly related to CFTR genotype but depends upon several parameters, including neutrophil-dominated inflammation. Identification of agents modulating inflammation constitutes a relevant goal. Myeloperoxidase (MPO) is involved in both microbicidal and proinflammatory neutrophil activities. The aim of this study was to evaluate whether the -463GA MPO promoter polymorphism is linked to clinical severity of CF-associated pulmonary inflammation. This polymorphism significantly affects the level of MPO gene expression in leukocytes and the G allele is more expressing than the A allele. We show that MPO genotype significantly influences the severity of pulmonary disease in early stages, prior to the development of chronic lung infections, with GG genotype being associated with more severe CF disease. Our findings indicate that the level of MPO gene expression influences the CF pathogenesis, presumably reflecting cellular damage by MPO-generated oxidants or other activity of MPO in airway inflammation.

Disease-associated mutations in human mannose-binding lectin compromise oligomerization and activity of the final protein

Deficiency of human mannose-binding lectin (MBL) caused by mutations in the coding part of the MBL2 gene is associated with increased risk and severity of infections and autoimmunity. To study the biological consequences of MBL mutations, we expressed wild type MBL and mutated MBL in Chinese hamster ovary cells. The normal MBL cDNA (WT MBL-A) was cloned, and the three known natural and two artificial variants were expressed in Chinese hamster ovary cells. When analyzed, WT MBL-A formed covalently linked higher oligomers with a molecular mass of about 300-450 kDa, corresponding to 12-18 single chains or 4-6 structural units. By contrast, all MBL variants formed a dominant band of about 50 kDa, with increasingly weaker bands at 75, 100, and 125 kDa corresponding to two, three, four, and five chains, respectively. In contrast to WT MBL-A, variant MBL formed noncovalent oligomers containing up to six chains (two structural units). MBL variants bound ligands with a markedly reduced capacity compared with WT MBL-A. Mutations in the collagenous region of human MBL compromise assembly of higher order oligomers, resulting in reduced ligand binding capacity and thus reduced capability to activate complement.

Genetic variation and hematology: single-nucleotide polymorphisms, haplotypes, and complex disease

In the course of generating a draft sequence of the human genome, we now recognize the enormous scope of genetic variation among humans, which can be used to probe the genetics of complex diseases such as leukemia or thrombosis. There is already mounting evidence of new susceptibility genes and genes that interact with environmental factors. Genetic variants, especially single-nucleotide polymorphisms (SNPs), also can be utilized to investigate potential modifiers of disease. Genetic variation can be applied to study pharmacogenomics, which could eventually drive the choice of therapeutic and interventional strategies. The genomic revolution ultimately should give insights into key mechanisms in hematological disorders that can be translated into targeted therapies.

Genetic variation in immune function and susceptibility to human filariasis

The generation of a draft sequence of a the human genome has provided the opportunity to characterize human diversity, even as it pertains to differences in host response to parasitic infection with organisms that cause lymphatic filariasis, malaria and schistosomiasis. Worldwide, human infection with filarial pathogens represents a significant cause of morbidity throughout the tropics. In particular, epidemiologic evidence suggests that a genetic component contributes to susceptibility and possibly the outcomes of filarial infection. Different approaches can be applied in population-based studies in areas where filarial infection is endemic, such as genome linkage scans and candidate gene analysis for the purpose of identifying genetic risk factors. This review summarizes recent advances in our understanding of genetic contributions to human lymphatic filariasis and addresses the immediate questions facing the field. It is anticipated that the identification of susceptibility genes in filarial infection could provide new insights into therapeutic strategies, including pharmacological intervention and vaccine development, and influence public health measures to control or avert infection.

Effects of glutathione S-transferase P1, M1, and T1 on acute respiratory illness in school children

The relationships between glutathione S-transferase (GST) M1, GSTT1, and GSTP1 genotypes and acute respiratory illness were investigated in a cohort of fourth grade school children aged 9-11 years who resided in 12 southern California communities. We used respiratory illness-related absences as a measure of respiratory illness occurrence. We ascertained respiratory illness-related school absences using an active surveillance system from January 1996 through June 1996. Genotypes for GSTM1 (null versus present), GSTT1 (null versus present), and GSTP1 (Ile105Val) were determined using genomic DNA from buccal cell specimens. The effects of GST genotypes on respiratory illness were assessed using stratified absence incidence rates and Poisson regression models. GSTP1 genotype was associated with risk for respiratory illness severe enough to result in a school absence. Children who were homozygous for the Val105 variant allele had lower incidence rates of upper and lower respiratory illnesses than did children who were homozygous for the Val105 allele. Children inheriting at least one Val105 allele were protected from respiratory illnesses (relative risk, 0.80; 95% confidence interval, 0.65-0.99). GSTM1 and T1 genotypes were not associated with respiratory illness. We conclude that GSTP1 genotype influences the risk or severity of respiratory infections in school-aged children.

One gene and one outcome? No way

The world of molecular diagnostics is undergoing major change because of both technical advances and the availability of rapidly expanding genetic databases generated by the study of human genomics. These resources comprise an extraordinary opportunity to decipher the biological importance of genetic aberrations, and link our understanding with clinical utility. The challenge lies in sorting through the information and developing effective strategies to advance molecular diagnostics.

Genetic polymorphisms in molecules of innate immunity and susceptibility to infection with Wuchereria bancrofti in South India

A pilot study was conducted to determine if host genetic factors influence susceptibility and outcomes in human filariasis. Using the candidate gene approach, a well-characterized population in South India was studied using common polymorphisms in six genes (CHIT1, MPO, NRAMP, CYBA, NCF2, and MBL2). A total of 216 individuals from South India were genotyped; 67 normal (N), 63 asymptomatic microfilaria positive (MF+), 50 with chronic lymphatic dysfunction/elephantiasis (CP), and 36 tropical pulmonary eosinophilia (TPE). An association was observed between the HH variant CHIT1 genotype, which correlates with decreased activity and levels of chitotriosidase and susceptibility to filarial infection (MF+ and CP; P = 0.013). The heterozygosity of CHIT1 gene was over-represented in the normal individuals (P = 0.034). The XX genotype of the promoter region in MBL2 was associated with susceptibility to filariasis (P = 0.0093). Since analysis for MBL-sufficient vs insufficient haplotypes was not informative, it is possible the MBL2 promoter association results from linkage disequilibrium with neighboring loci. We have identified two polymorphisms, CHIT1 and MBL2 that are associated with susceptibility to human filarial infection, findings that merit further follow-up in a larger study.

Variant genotypes of FcγRIIIA influence the development of Kaposi's sarcoma in HIV-infected men

Disturbances in inflammatory cytokine production and immune regulation coupled with human herpesvirus-8 (HHV-8) infection underlie the current understanding of the pathogenesis of Kaposi's sarcoma (KS), the most common HIV-associated malignancy. The low affinity Fc gamma receptors (FcγR) for IgG link humoral and cellular immunity by mediating interaction between antibodies and effector cells, such as phagocytes and natural killer cells. We examined the frequency of polymorphic forms of the low affinityFcγRs, FcγRIIA,FcγRIIIA, and FcγRIIIB in 2 cohorts of HIV-infected men with KS and found that theFcγRIIIA genotype exerts a significant influence on susceptibility to or protection from KS. The FF genotype was underrepresented in patients with KS, whereas the VF genotype was associated with development of KS. A similar association was observed between FcγRIIIA genotypes and HHV-8 seropositivity. These observations suggest a possible role forFcγRIIIA in the development of KS during HIV infection.

Variant genotypes of FcγRIIIA influence the development of Kaposi's sarcoma in HIV-infected men

Disturbances in inflammatory cytokine production and immune regulation coupled with human herpesvirus-8 (HHV-8) infection underlie the current understanding of the pathogenesis of Kaposi's sarcoma (KS), the most common HIV-associated malignancy. The low affinity Fc gamma receptors (FcγR) for IgG link humoral and cellular immunity by mediating interaction between antibodies and effector cells, such as phagocytes and natural killer cells. We examined the frequency of polymorphic forms of the low affinityFcγRs, FcγRIIA,FcγRIIIA, and FcγRIIIB in 2 cohorts of HIV-infected men with KS and found that theFcγRIIIA genotype exerts a significant influence on susceptibility to or protection from KS. The FF genotype was underrepresented in patients with KS, whereas the VF genotype was associated with development of KS. A similar association was observed between FcγRIIIA genotypes and HHV-8 seropositivity. These observations suggest a possible role forFcγRIIIA in the development of KS during HIV infection.

Mining variations in genes of innate and phagocytic immunity: current status and future prospects

The large number of sequence variations in human genes reflects the diversity of human populations and the response to prior environmental and pathogen challenges. Currently, major efforts are under way to identify and catalog single-nucleotide polymorphisms for use in genetic studies designed to explore the contribution of common variants to both disease susceptibility and interindividual differences in outcomes. So far, the most productive approach has been to search with candidate genes for which there is a scientific rationale (eg, prior data on the biologic implications of one or more variant alleles). Recently, there has been an explosion in the number of genetic association studies seeking to correlate one or more well-defined outcomes with variant alleles. These studies provide a foundation for identifying and applying genetic risk factors to clinical medicine. However, a number of challenges must be met before widespread use in clinical medicine can be undertaken. These include more efficient bioinformatics, basic insights into the significance of the variant alleles, ethical issues, and the availability of cost-effective, high-throughput platforms for genotype analysis.