|
Post by Admin on Oct 7, 2019 18:03:45 GMT
TLR2 Cluster Genes Are Involved in the Recognition of Yersinia pestis. TLR2 recognition of V-antigen and LcrV of Y. pestis is the main recognition mechanism during plague. TLR2 forms heterodimers with receptors of the same gene cluster (TLR1/TLR6) for recognition of bacterial lipopeptides (16), but it is not known whether TLR2 also collaborates with TLR10 for the recognition of Y. pestis. We transfected HEK cells (that normally express TLR1 and TLR6) with TLR2, TLR10, or TLR2 and TLR10. The HEK cells transfected with TLR2 alone release significantly more cytokines than untransfected cells: twofold more for Y. pestis and fivefold more for Yersinia pseudotuberculosis, the microorganisms from which Y. pestis evolved (Fig. 3A). Although TLR10 by itself is not able to induce cytokine production, cotransfection of TLR10 with TLR2 completely abrogates the stimulatory effect of TLR2 (Fig. 3A). These data were supported by blocking TLR2 in monocytes using monoclonal antibodies (Fig. 3 B–D). Interestingly, blocking TLR10 resulted in an increase in cytokine production (Fig. 3 B–D), supporting the observation that TLR10 has a modulatory effect, thus corroborating the overexpression experiments. Fig. 3. The role of TLR10 for the recognition of Y. pestis and Y. pseudotuberculosis. (A) HEK293 transiently transfected with TLR2, TLR10, or TLR2/10, and stimulated with 1 × 105 heat-inactivated Y. pestis or Y. pseudotuberculosis, respectively. Bars represent the means ± SEM of at least three separate experiments. (B) PBMCs stimulated with Y. pestis or Y. pseudotuberculosis per mL. n = 6; means ± SEM; *P = 0.05, **P = 0.01. (C) TNF-α production after PBMCs stimulated with Y. pestis or Y. pseudotuberculosis in the presence or absence of 10 µg/mL antibody. (D) IL-1β production after 24 h of stimulation. Means ± SEM; *P = 0.05, **P = 0.01. The data shown are from three independent experiments each performed in duplicate. The modulatory effects of TLR10 seem to be exerted specifically on TLR2 signaling, as anti-TLR10 antibodies modulated cytokine production induced by palmitoyl-3-cysteine-serine-lysine-4, but not by the TLR4 agonist LPS (Fig. S4). Moreover, when cells of individuals carrying the SNP in TLR10 were exposed to either LPS, Poly I:C, CpG, or flagellin, no differences between the groups could be detected (Fig. S5). Interestingly, however, cross-linking of TLR10 receptors inhibited the IL-6 induction by IL-1 (Fig. S6), suggesting that TLR10 may exert inhibitory effects on the IL-1 family of cytokines (17). Fig. 4. Functional consequences of human TLR1/TLR6/TLR10 SNPs for Y. pestis–stimulated cytokine production. PBMCs from healthy volunteers stimulated with different stimuli, including Y. pestis (1 × 105/mL). Volunteers were separated into three groups: one group did not display the SNP in either TLR1 (A/B), TLR6 (C/D), or TLR10 (E/F; wt, wild-type); one group was heterozygous for the polymorphism (He); and one group was homozygous (Ho). Data are means ± SEM. *P = 0.05, **P = 0.01, ***P = 0.001. Common TLR1, TLR6, and TLR10 Polymorphisms in European Populations Modulate Cytokine Responses to Y. pestis. To demonstrate that TLR1, TLR6, and TLR10 genetic variation in the population modulates the response to Y. pestis, we isolated peripheral blood mononuclear cells (PBMCs) from a group of 101 individuals of European descent and exposed them to the pathogen. SNPs in TLR1, TLR6, and TLR10 significantly influenced cytokine production induced by Y. pestis and Y. pseudotuberculosis (Fig.4 and Fig. S7). In contrast, known polymorphisms in TLR4 (Asp299Gly and Thre399Ile) did not influence the response of PBMCs to Y. pestis or Y. pseudotuberculosis (Fig. S8).
|
|
|
Post by Admin on Oct 8, 2019 18:17:23 GMT
Discussion In this study, we identified a set of genes evolving under positive selection in populations of different ethnic ancestry living in Europe, but not in Northwest India. Among these genes, the region encompassing TLR1, TLR6, and TLR10 is under selection in Europeans/Romanians and Rroma/Gypsies, but not in a population from Northwest India. The common selection pressures in the Romanians and Rroma may be interpreted as the same evolutionary process induced by local infectious conditions in two European populations of different genetic backgrounds. To look for more evidence on positive selection in European populations, we analyzed sequence data from the 1000 Genome Project (18). These data show a clear selective sweep in Europeans using two methods based on genetic differentiation and extended linkage disequilibrium haplotype [cross-population extended haplotype homozogysity (XP-EHH) and XP-CLR]. This signal was specific in Europeans and absent in an African population (Yoruba) and in a Chinese population (Fig. S9).
Besides the TLR2 gene cluster, other genes of interest include (i) a gene cluster with four genes in chromosome 5 that contains the well-known gene SLC45A2 being under positive selection in relation to skin pigmentation; (ii) FBXL19, a gene known to be involved in the modulation of inflammation (19) in a cluster comprising three genes; and (iii) ADAMTS12 gene, which is associated with susceptibility to autoimmune diseases (20). In the same cluster as the SLC45A2 gene, other genes (Table 1) may be of special interest to be analyzed functionally in the future.
Linguistic and genetic studies suggested that the Rroma population left India in the 5–10th centuries and started to settle in Europe during the 11th century (21). Genetic studies, focused on uniparental and Mendelian disease markers, confirmed Rroma as an isolated population of Indian origin among the European majority (7). We pose that after the Rroma migration, the infectious pressures to which the Rroma were exposed were the same as for the Europeans, whereas for the ancestral North Indian population, they remain linked to their geographical location in India. This peculiar demographic situation in Europe, in which populations with different genetic backgrounds have been exposed for a long period to similar infection pressures, gave us the opportunity to attempt the reconstruction of recent evolutionary events acting on the immune system of populations living in Europe.
An important question is which evolutionary pressures were common to the Romanian and Rroma populations. Infections are likely to have been one of the most important evolutionary forces shaping the immune system in both Europe and India, and several candidates may be considered. An infection often associated with evolutionary effects in Europeans is plague, responsible for several large epidemics with death rates of up to 30–50% of the European population and lingering thereafter in Europe for several centuries (22), thus allowing for the exertion of selective sweeps. Based on this extreme burden of mortality, it is rational to hypothesize that plague had major evolutionary effects on the immune system of European populations. The TLR/IL-1 functional cluster is crucial for host defense against Y. pestis: TLR2 and its coreceptors TLR1, TLR6, and TLR10 are the main pattern recognition receptors for Y. pestis—all localized in a single gene cluster in chromosome 4 (23), whereas Y. pestis Caf1 protein is an inhibitor of IL-1β (24). Decreased IL-1 responses, either through defective TLR signaling or release of Caf1, are likely to have deleterious effects on host survival. The data presented here show that the TLR1/TLR6/TLR10 receptor cluster has been under positive selection in both Romanians and Rroma, and suggest that plague is a potential infection that has exerted this selection. Our data are also supported by an earlier study that identified the TLR1/TLR6/TLR10 gene cluster as a target of recent positive selection in non-Africans (25). We confirmed the functional impact of TLR1, TLR6, and TLR10 polymorphisms currently present in Europeans for the immune responses to Y. pestis.
Although evolutionary pressure exerted by plague is a plausible cause of adaptive selection, it should be emphasized that other infections in which the receptors of the TLR2 cluster play a central role, such as tuberculosis, leprosy, or common Gram-positive pathogens, could have also contributed to the genetic pattern observed here. Nevertheless, these infections have a generally less restricted geographical pattern as common in India as in Europe. Importantly, the impact of historical plagues in India has been a matter of debate. Out of the three main outbreaks of plague (6–7th centuries, 14th century, and turn of 19–20th century), by far the most devastating is the second, called the Black Death. This outbreak is known not to have affected India (26) and took place after the settlement of Rroma in Europe. Indeed, the Indian subcontinent may have been the only part of Eurasia to have experienced steady population growth during the last half of the 14th century, and the first reports of plague are from the 17th century, with much less impact than the Black Death. During the epidemics in the Indian subcontinent, the disease behaved differentially than plague in the 14th century in Europe, with less than 5% human mortality. It is likely that the absence of the flea Xenopsylla cheopis due to tropical environment and the distance and geographical barriers could have prevented the entrance of the devastating outbreak of the Middle Ages into India (26).
The identification of the immune pathways and genetic variants that were specifically selected in Europe not only helps us to understand the evolutionary history of European populations, but also contributes to our understanding of the differences in susceptibility between European and other populations to modern human diseases. Evolutionary pressure exerted by plague or smallpox has been previously proposed to partly explain the increased resistance to HIV in Europeans (6). In addition, the evolution toward a proinflammatory profile induced by infections during history might explain the burden of autoimmune diseases in modern human populations (27). Genetic variation in TLR7 and TLR8 has been shown to protect against viral infections (25), while predisposing some to autoimmune diseases (4). Similarly, TLR1 or TLR10 polymorphisms can protect against infections, while being associated with autoinflammatory diseases such as sarcoidosis (28) and Crohn’s disease (29). Although the differences in cytokine production induced by Y. pestis in individuals with various TLR1, TLR6, or TLR10 polymorphisms are moderate from an immunological point of view, they are large from an evolutionary perspective, and can lead in the long term to significant shifts in the population. It should be realized that we may not have detected other genes relevant for host defense that may be under selective pressure, as they have not been included in the Illumina immunochip array, and only future studies using genome-wide sequencing have the capacity to provide an exhaustive analysis of the entire genome.
In conclusion, by comparing genes under selection in European/Romanian and Rroma/Gipsy populations, we identified several immunological pathways specifically shaped by evolutionary processes in populations living together in Europe during the last millennium. It is likely that the selection pressure at least on some of these genes has been exerted by plague epidemics, and we identify the TLR1/TLR6/TLR10 pattern recognition system as a likely candidate.
PNAS February 18, 2014 111 (7) 2668-2673
|
|
|
Post by Admin on Oct 8, 2019 22:14:36 GMT
The ancestral bacteria is thought to come from a town called Laishevo in Russia, based on an ancient evidence sample called LAI009. The researchers explained in their paper: "Our phylogenetic reconstruction shows that the LAI009 isolate from Laishevo is ancestral to the Black Death isolates from southern, central, western and northern Europe, as well as to the previously published late 14th-century isolates from London and Bolgar City. "We interpret LAI009 as the most ancestral form of the strain that entered Europe during the initial wave of the second pandemic that has been identified to date." It was previously thought that the Black Death originated in Central Asia and was carried to Europe by fleas living on black rats that travelled on all merchant ships. Spyrou admitted: "It is possible that additional interpretations may be revealed with future discoveries of unsampled diversity in western Eurasia." Fig. 2 The researchers cannot be certain that they have found the definitive origin of the Black Death but their work does help to illustrate some of the earliest known origins of the second plague pandemic. They concluded in their paper: "The second plague pandemic has arguably caused the highest levels of mortality of the three recorded plague pandemics. "It serves as a classic historical example of rapid infectious disease emergence, long-term local persistence and eventual extinction for reasons that are currently not understood."
|
|
|
Post by Admin on Oct 9, 2019 18:17:53 GMT
The Black Death was only the beginning. Countless millions perished in this terrible early wave – an estimated 60 percent of Europe was wiped out – but the virulent bacterium responsible was never actually contained. When the Black Death of the mid–14th century was over, Yersinia pestis was far from done, laying waste to human life for another 500 years. This grim, recurring saga of outbreaks – called the second plague pandemic – lasted until the 19th century. But where did its deadly antagonist originate? In a new study, an international team of scientists reconstructed 34 Y. pestis genomes sourced from the teeth of 34 individuals who died in 10 different countries – tracing a kind of genetic family tree of shadowy pestilence spanning the 14th to 17th centuries. The family tree, encompassing the remains of people who were infected by the bacterium in England, France, Germany and elsewhere, reveals a diversification of the Y. pestis lineage over time into multiple genetically distinct clades. Nonetheless, these clades appear to have one common starting point. "These findings indicate a single entry of Y. pestis into Europe through the east", says archaeogeneticist Maria Spyrou from the Max Planck Institute for the Science of Human History, on the basis that one strain in particular looks to be the ancestor of all the second plague pandemic strains that came after it. The precursor, the researchers say, came from Russia, specifically a town called Laishevo in the historical Volga region, based on the evidence of a sample known as LAI009. "Our phylogenetic reconstruction shows that the LAI009 isolate from Laishevo is ancestral to the Black Death isolates from southern, central, western and northern Europe, as well as to the previously published late 14th-century isolates from London and Bolgar City," the researchers explain in their paper. "We interpret LAI009 as the most ancestral form of the strain that entered Europe during the initial wave of the second pandemic that has been identified to date." Of course, in reconstructions like this, conclusions are necessarily limited by the scope of skeletal remains you get to dig up and study. In other words, the researchers acknowledge it's entirely possible that the pestilence – in this era of history, at least – may have had earlier forms in other places that have not yet been sufficiently tested. "It is possible that additional interpretations may be revealed with future discoveries of unsampled diversity in western Eurasia," Spyrou says.
|
|
|
Post by Admin on Oct 10, 2019 21:57:58 GMT
Abstract On the basis of a 14th-century account by the Genoese Gabriele de’ Mussi, the Black Death is widely believed to have reached Europe from the Crimea as the result of a biological warfare attack. This is not only of great historical interest but also relevant to current efforts to evaluate the threat of military or terrorist use of biological weapons. Based on published translations of the de’ Mussi manuscript, other 14th-century accounts of the Black Death, and secondary scholarly literature, I conclude that the claim that biological warfare was used at Caffa is plausible and provides the best explanation of the entry of plague into the city. This theory is consistent with the technology of the times and with contemporary notions of disease causation; however, the entry of plague into Europe from the Crimea likely occurred independent of this event. The Black Death, which swept through Europe, the Near East, and North Africa in the mid-14th century, was probably the greatest public health disaster in recorded history and one of the most dramatic examples ever of emerging or reemerging disease. Europe lost an estimated one quarter to one third of its population, and the mortality in North Africa and the Near East was comparable. China, India, and the rest of the Far East are commonly believed to have also been severely affected, but little evidence supports that belief (1). A principal source on the origin of the Black Death is a memoir by the Italian Gabriele de’ Mussi. This memoir has been published several times in its original Latin (2,3) and has recently been translated into English (4) (although brief passages have been previously published in translation, see reference [5]). This narrative contains some startling assertions: that the Mongol army hurled plague-infected cadavers into the besieged Crimean city of Caffa, thereby transmitting the disease to the inhabitants; and that fleeing survivors of the siege spread plague from Caffa to the Mediterranean Basin. If this account is correct, Caffa should be recognized as the site of the most spectacular incident of biological warfare ever, with the Black Death as its disastrous consequence. After analyzing these claims, I have concluded that it is plausible that the biological attack took place as described and was responsible for infecting the inhabitants of Caffa; however, the event was unimportant in the spread of the plague pandemic. Origin of the 14th-Century Pandemic Figure 1. Tentative chronology of the initial spread of plague in the mid-14th century (12–14). The disease that caused this catastrophic pandemic has, since Hecker (6), generally been considered to have been plague, a zoonotic disease caused by the gram-negative bacterium Yersinia pestis, the principal reservoir for which is wild rodents (7–11). The ultimate origin of the Black Death is uncertain—China, Mongolia, India, central Asia, and southern Russia have all been suggested (see Norris [1] for a discussion of the various theories). Known 14th-century sources are of little help; they refer repeatedly to an eastern origin, but none of the reports is first-hand. Historians generally agree that the outbreak moved west out of the steppes north of the Black and Caspian Seas, and its spread through Europe and the Middle East is fairly well documented (Figure 1). However, despite more than a century of speculation about an ultimate origin further east, the requisite scholarship using Chinese and central Asian sources has yet to be done. In any event, the Crimea clearly played a pivotal role as the proximal source from which the Mediterranean Basin was infected.
|
|