Biology subjects

Segal, A. W.

Publications and source records attributed to Segal, A. W..

3 recordsLinked to original sources

bioRxiv2018

Variations in the phagosomal environment of human neutrophils and mononuclear phagocyte subsets.

The phagosomal microenvironment has a major influence on the enzyme activity and biology within these organelles. Here we directly compared the phagosomal pH of human neutrophils, monocytes, dendritic cell (DC) and monocyte-derived cells. An unexpected observation was the striking difference in phagosomal environment between the three monocytes subsets. Classical monocytes and neutrophils had alkaline phagosomes, yet non-classical monocytes had more acid phagosomes. Intermediate monocytes had an intermediate phenotype. We next investigated the differences between primary DCs versus in vitro monocyte-derived DCs and established that both these cells had acidic phagosomal environments. We also confirmed reports of an alkaline phagosome in \"M1\" macrophages, and an acidic one in \"M2\" macrophages. Across all phagocytes, alkalinisation was dependent upon the activity of the NADPH oxidase, as when it was absent in cells from a patient with chronic granulomatous disease (CGD) or was abolished by an inhibitor of the oxidase, diphenyleneiodonium (DPI). An increased alkalinity in the phagosome was associated with more oxidase activity. These data highlight the heterogenous nature of phagocytic vacuoles within the family of mononuclear phagocytes that will dictate the function of these compartments.\n\nKey pointsO_LIPhagosomal function depends upon the action of enzymes released into them from cytoplasmic granules.\nC_LIO_LIThe substantial differences in the phagosomal pH in the different phagocytes will affect their compliment of enzymes and their functions.\nC_LI

immunology↗

bioRxiv2018

Evidence against the microbicidal action of neutrophil extracellular traps (NETs)

Neutrophil extracellular traps (NETs) are fibrillary structures composed of extruded nuclear chromatin decorated with granule proteins (mostly neutrophil elastase, cathepsin G and myeloperoxidase). It has been reported that NETs are able to kill bacteria and fungi based upon the observation that smaller number of organisms are obtained in plating assays after they are incubated with NETs than if the DNA is pre-digested with DNase. It is possible that the microbial killing is apparent rather than real, and occurs because the organisms are aggregated on the DNA structure, and that the plating assay results were simply misinterpreted. The present study shows that digestion of DNA after incubation of NETs with the microbes restores their numbers to preincubation levels indicating that the apparent killing is an artefact of the assay.

immunology↗

bioRxiv2017

The human oral microbiome is shaped by shared environment rather than genetics: evidence from a large family of closely-related individuals

The human microbiome is affected by multiple factors, including the environment and host genetics. In this study, we analyzed the oral microbiome of an extended family of Ashkenazi Jewish individuals living in several cities and investigated associations with both shared household and host genetic similarities. We found that environmental effects dominated over genetic ones. While there was weak evidence of geographic structuring at the level of cities, we observed a large and significant effect of shared household on microbiome composition, supporting the role of immediate shared environment in dictating the presence or absence of taxa. This effect was also seen when including adults who had grown up in the same household but moved out prior to the time of sampling, suggesting that the establishment of the oral microbiome earlier in life may affect its long-term composition. We found weak associations between host genetic relatedness and microbiome dissimilarity when using family pedigrees as proxies for genetic similarity. However this association disappeared when using more accurate measures of kinship based on genome-wide genetic markers, indicating that environment rather than host genetics is the dominant factor affecting the composition of the oral microbiome in closely-related individuals. Our results support the concept that there is a consistent core microbiome conserved across global scales, but that small-scale effects due to shared living environment significantly affect microbial community composition.\n\nIMPORTANCEPrevious research shows that relatives have a more similar oral microbiome composition than non-relatives, but it remains difficult to distinguish the effects of relatedness and shared household environment. Furthermore, pedigree measures may not accurately measure host genetic similarity. In this study, we include genetic relatedness based on genome-wide SNPs (rather than pedigree measures) and shared environment in the same analysis. We quantify the relative importance of these factors by studying the oral microbiome in members of a large extended Ashkenazi Jewish family who share a similar diet and lifestyle despite living in different locations. We find that host genetics plays no significant role and that the dominant factor is shared environment at the household level. We also find that this effect appears to persist in individuals who have moved out of the parental household, suggesting that the oral microbiome established earlier in life persists long-term.

microbiology↗