RESUMEN
LPS binding protein (LBP) is an important innate sensor of microbial cell wall structures. Frequent functionally relevant mutations exist and have been linked to influence susceptibility to and course of bacterial infections. We examined functional properties of a single nucleotide polymorphism resulting in an exchange of phenylalanine to leucine at position 436 of LBP (rs2232618) and compared the frequent variant of the molecule with the rare one in ligand binding experiments. We then stimulated RAW cells with bacterial ligands in the presence of serum obtained from individuals with different LBP genotypes. We, furthermore, determined the potential effects of structural changes in the molecule by in silico modeling. Finally, we analyzed 363 surgical patients for this genetic variant and examined incidence and course of sepsis following surgery. We found that binding of LBP to bacterial ligands was reduced, and stimulation of RAW cells resulted in an increased release of TNF when adding serum from individuals carrying the F436L variant as compared with normal LBP. In silico analysis revealed structural changes of LBP, potentially explaining some of the effects observed for the LBP variant. Finally, patients carrying the F436L variant were found to be similarly susceptible for sepsis. However, we observed a more favorable course of severe infections in this cohort. Our findings reveal new insights into LPS recognition and the subsequent activation of the innate immune system brought about by LBP. The identification of a genetic variant of LBP influencing the course of sepsis may help to stratify individuals at risk and thus reduce clinical complications of patients.
Asunto(s)
Proteínas de Fase Aguda/genética , Proteínas de Fase Aguda/fisiología , Proteínas Portadoras/genética , Proteínas Portadoras/fisiología , Variación Genética/genética , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/fisiología , Sepsis/genética , Sepsis/inmunología , Animales , Línea Celular , Simulación por Computador , Genotipo , Humanos , Ratones , Polimorfismo de Nucleótido SimpleRESUMEN
Lipopolysaccharide (LPS) binding protein (LBP) is an acute-phase protein that initiates an immune response after recognition of bacterial LPS. Here, we report the crystal structure of murine LBP at 2.9 Å resolution. Several structural differences were observed between LBP and the related bactericidal/permeability-increasing protein (BPI), and the LBP C-terminal domain contained a negatively charged groove and a hydrophobic "phenylalanine core." A frequent human LBP SNP (allelic frequency 0.08) affected this region, potentially generating a proteinase cleavage site. The mutant protein had a reduced binding capacity for LPS and lipopeptides. SNP carriers displayed a reduced cytokine response after in vivo LPS exposure and lower cytokine concentrations in pneumonia. In a retrospective trial, the LBP SNP was associated with increased mortality rates during sepsis and pneumonia. Thus, the structural integrity of LBP may be crucial for fighting infections efficiently, and future patient stratification might help to develop better therapeutic strategies.
Asunto(s)
Proteínas de Fase Aguda/química , Péptidos Catiónicos Antimicrobianos/química , Proteínas Sanguíneas/química , Proteínas Portadoras/química , Inmunidad Innata/genética , Lipopolisacáridos/química , Glicoproteínas de Membrana/química , Modelos Moleculares , Mutación , Polimorfismo de Nucleótido Simple , Proteínas de Fase Aguda/genética , Proteínas de Fase Aguda/inmunología , Animales , Péptidos Catiónicos Antimicrobianos/genética , Péptidos Catiónicos Antimicrobianos/inmunología , Sitios de Unión , Proteínas Sanguíneas/genética , Proteínas Sanguíneas/inmunología , Proteínas Portadoras/genética , Proteínas Portadoras/inmunología , Cristalografía por Rayos X , Genotipo , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Lipopolisacáridos/inmunología , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/inmunología , Ratones , Unión Proteica , Estructura Terciaria de Proteína , Electricidad Estática , Homología Estructural de ProteínaRESUMEN
OBJECTIVES: Toll-like receptors (TLRs) play an important role in the innate immune response to pathogens. TLR7 recognizes RNA of various viruses including HIV. The objective of this study was to examine the influence of individual genetic variations of TLR7 on the susceptibility to and progression of HIV disease. METHOD: We genotyped a population of 734 HIV-positive adults and 545 healthy controls for three TLR7 single nucleotide polymorphisms. The frequency of TLR7 genetic variations was assessed and related to HIV disease progression. Furthermore, we analyzed peripheral blood mononuclear cells obtained from healthy individuals differing in their TLR7 genotype and assessed their response to a TLR7-specific ligand ex vivo. RESULTS: Presence of the most frequent TLR7 polymorphism, TLR7 Gln11Leu, was associated with higher viral loads and accelerated progression to advanced immune suppression in HIV patients. Furthermore, in women this polymorphism may be associated with increased HIV-1 susceptibility as it was found more frequently among patients as compared with controls. Peripheral blood mononuclear cells from polymorphism carriers secreted significantly less IFN-alpha following TLR7 activation, whereas IL-6 production remained unaltered. CONCLUSION: This is the first report of a functional TLR7 variant to be associated with susceptibility to and a more severe clinical course of HIV-1 disease. These results may have implications for the risk assessment of individual patients as well as for HIV-1 therapy and vaccination strategies in the future.