Ants doing gene therapy, and tadpole microbiomes
This month, as the eLife Podcast hits its century, we hear how getting frog dads to cross-foster tadpoles has revealed the way in which some frogs come by their microbiomes, the ants that do gene therapy, signs that disease causes a breakdown in nutrient exchange between the elements of the microbiome, how fungi reprogram immune cells to cause over-reactions in sepsis, and new insights into how tapeworm larvae in the brain cause seizures...
In this episode
00:51 - How poison arrow frogs come by their microbiomes
How poison arrow frogs come by their microbiomes
Maisie Fischer, University of Vienna
How do frogs come by their microbiomes? We know that a human baby picks up its microbiome as it makes its entry into the world, usually in the form - as one microbiologist put it - of a mouthful of muck. Amphibians, though, develop in spawn as a tadpole. So what’s their story? This is an important nut to crack because of the threat posed to these creatures by a rampant “chytrid” fungus, first documented as a threat about 20 years ago. Maisie Fischer is at the University of Vienna…
Maisie - We're currently witnessing the greatest loss of biodiversity that can be attributed to a pathogen, and that pathogen is a fungus and it targets various species of amphibians. This fungus infects and destroys their skin, which would usually kill them. However, we know that skin microbiome can protect amphibians from these infections. And so I set out to explore how and when skin microbiota of tadpoles are acquired. And in this regard, I was particularly interested to find out about the role of parental care in this process.
Chris - Which amphibians were you looking at specifically?
Maisie - So because I was particularly interested in the parental care aspect, I chose amphibians that show like a high diversity of parental care strategies. So I was working with poison frogs, and one particular, which is the variable poison frog, very colourful, day active, which makes the life of us as scientists much easier. And they are also dedicated parents. So as many poison frogs, they deposit their clutch terrestrial because they live in the neotropics, where the high humidity allows them to do so. However, when the tadpoles develop far enough, they still need to be transported to water to complete their development. And so these parents check regularly on their eggs. And then once the tadpoles are ready, they help them hatch. And then the dad actually does the parental care, and he takes these tadpoles onto his back, piggyback. He then transports them to tiny pools of water that form in plants. And so I was interested in whether we have microbiota transferred from the dad to the offspring in the course of this transport period.
Chris - And are the tadpoles, before they're a tadpole, when they're developing in their egg stage, are they sterile at that stage? So there's no microbes on them at that stage, and then they pick up microbes from their environment and their dad, potentially, after hatching. Is that sort of where you were coming from?
Maisie - Yes. So that was the very first question that I wanted to answer. People had not thought about the tadpoles being sterile at that point. However, other vertebrate eggs, for example, chicken eggs, the embryo is surrounded by a membrane that is called the vitilin envelope. And this envelope serves as microbial barrier. And so just because chicken are much more interesting to human beings because of their importance for human nutrition, this is very well investigated, and nobody has ever looked at that in frogs. And so this was the very first question of my whole project that I wanted to answer. When can microbes actually access the embryo?
Chris - And is that the case, that the tadpoles, before they escape from the egg, are sterile, and as soon as they're out into the environment, that's when they pick up bugs?
Maisie - So we found that the content of microbes in the surrounding jelly, so the egg surrounding the embryo, is much higher than in the embryo itself. So this is a good hint that actually the vitilin envelope also in tadpoles protects the embryo from major microbial colonisation. So this colonisation will just occur after these tadpoles are old enough to hatch from the vitilin envelope, which in our study species happens right before they are transported.
Chris - And then when dad picks them up, is there evidence that there is a colonisation of the tadpole with the parental microbiome at that stage?
Maisie - Yes. I see this as one of the major achievements of this research, that we could actually provide the very first evidence that this is indeed happening during tadpole transport. It doesn't seem to happen in the egg because the embryo is still protected. However, during tadpole transport, there is a direct skin-to-skin contact between the dad and the tadpole. And so we used an experiment where we could actually trace the microbes found in a tadpole after they had been transported. To do that, we used the fact that skin microbiota are influenced by the species. That means that different species of poison frog have very distinct skin microbiota. And so what we did was that we worked with sibling tadpoles and we had one tadpole transported by the biological dad and fostered a second tadpole onto the back of a very different poison frog species. And so that helped us show that whatever species transported that tadpole, this microbiota can then be found on the tadpole skin.
Chris - And it also nails the question, well, they didn't just pick up their particular unique clutch of microbes from the environment. They must have got it from the dad because otherwise both of those experiments would have ended up ultimately with the same microbiome, which they didn't.
Maisie - Exactly. So the other question was whether probably tadpoles can also spend a lot of time in the jelly already acquiring some microbiota there. And that was like one of the major reasons to choose this species, because in our species that dad actually helps the tadpoles hatch. And so if this is the case, really like microbiota of the transporting frogs are like among the very first microbiota that these tadpoles encounter. And they are definitely transferred from the transporting frog to the tadpole in the course of this transport.
07:41 - Microbiome diversity and host disease
Microbiome diversity and host disease
Iva Veseli, Helmholtz Institute for Functional Marine Biodiversity
The microbiome is often regarded as “the organ that everyone formerly overlooked”; in us, it’s the assemblage of 50 trillion plus bacteria, fungi and viruses that live in us and on us, see our dinner before we do, detoxify poisons, train our immune system, liberate calories we otherwise couldn’t access, and fend off infections by microbial nasties we want to exclude. And one observation that has been made is that when we get ill, the microbiome is often off-kilter too. But what came first? Did the disruption to the microbiome lead to a disease domino effect, or did the disease alter our biochemistry and that, in turn, destabilised the microbiome? Well, it looks like it’s the latter. As she explains to Chris Smith, Iva Veseli, at the Helmholtz Institute for Functional Marine Biodiversity, in Oldenburg, Germany, has found that in people with inflammatory bowel disease, who predictably have a deranged microbiome, it’s not so much that there’s a specific microbe spectrum linked to the disease: instead, the conditions seem to provoke a breakdown in the cooperation between the elements of the microbiome, so bugs that would formerly trade biochemicals among themselves cease to do so, and instead a community of biochemically independent microbes emerges…
Iva - One of the big open questions in the gut microbiome field is why does the diversity of the gut microbiome decrease in people who have gastrointestinal diseases or disorders? So many individuals who suffer from these conditions host fewer different types of microbes in their gut. So whereas a healthy person's gut might include thousands of different microbial populations, for a person with a health issue, that number is less. And this is an important question because what happens to the gut microbiome can inform how we treat or diagnose these conditions. So for instance, if we learn something about the gut microbiome being implicated in the cause of a disease, then we know that, oh, we can maybe treat this by changing the microbiome.
Chris - So is my microbiome more narrow when I have a gastrointestinal problem because some problem has led to it becoming more narrow or did it narrow and then cause my problem?
Iva - That's the big chicken versus the egg, what comes first kind of problem plaguing the gut microbiome field at the moment. Those two directions of causality are very complicated to disentangle. People have tried to do it via sort of associations of, okay, do we see certain kinds of microbes in people with diseases than in healthy people? But unfortunately, so far, there hasn't, at least for some of the diseases. So for instance, in our study, we specifically looked at inflammatory bowel disease or IBD. So at least for IBD, there isn't one blanket answer to, yes, these microbes seem to always appear in people with this disease. And so what that sort of implied to us was that there's not one sort of bad microbe that is sort of helping to cause the disease. The causality might be going in the other direction.
Chris - And how did you actually investigate that?
Iva - We looked at it from the angle of microbial metabolic activity and collaborations between different microbes. You might know that in the human gut and in fact, in a lot of different environments where microbes live, it's not like every microbe can produce all of the molecules that it needs for itself to live. Instead, some of the microbes can produce some of the stuff and some of the microbes can produce all of the stuff and they sort of exchange molecules between each other.
And this is a phenomenon known as cross-feeding, which is very common within the gut microbiome. Previous studies that had looked at the gut microbiome in disease conditions had started to see that these collaborations seem to be breaking down when disease happens. So we tried to look in a lot of different people who had inflammatory bowel disease and a lot of different people who are healthy. We tried to see, are these microbes having lots of metabolic capacity to produce their own compounds via biosynthesis pathways?
Chris - How did you do that? Did you literally take samples and test them?
Iva - So we actually took a computational approach to do this. So I wrote some software that is able to look at the DNA of multiple organisms in a community and predict from that DNA what sorts of metabolic activities the organisms can conduct. Stuff like this microbe can produce the amino acid proline, or this microbe can produce the nucleotide adenine. And from looking at those sorts of prediction data, we were able to assess, is the general biosynthetic capacity in the IBD gut microbiome higher than in the healthy gut microbiome? And the answer was yes.
Chris - So someone else had basically looked at the nuts and bolts of what bugs were there genetically, and it was that data that you could then use to then extract these metabolic implications from?
Iva - Indeed. So there's been lots of studies on the gut microbiome in inflammatory bowel disease. And we basically took a bunch of these public samples, they're called metagenomes because they basically contain all the microbes within a person's gut community. And then we were able to compare copy numbers of metabolic pathways encoded in the samples from each group.
Chris - So take us through then what you actually see, and then perhaps we can speculate as to why.
Iva - It turns out that in the gut communities in people with IBD, there's a lot more metabolic capacity per microbe than in the people with a healthy state. So what that practically means is generally in the IBD gut communities, the microbes that are living there can make a lot of stuff for themselves. So they're very self-sufficient. They don't rely on any other microbes in their surroundings to give them stuff. And in contrast, in the healthy group, those gut microbes are very interdependent. So they cannot make stuff for themselves, meaning that they need to get it from their neighbours, essentially.
Chris - It's like a breakdown in world trade, isn't it? When everyone's getting on very well, countries are trading with each other, and you don't need to have self-sufficiency because you can buy it from your neighbouring country. But when everyone falls out, then you have to have your own raw materials and do everything yourself just to make sure you've got enough of everything. Do you think that that then is again a cause of the acceleration of the disease or a consequence?
Iva - I certainly think that the gut microbiome is not the initial, at least not a major initial cause of someone getting a disease. And the other way around, when someone has a disease, you know, their immune system activity, the drugs that they take to manage their symptoms, those all exhibit a stress on the gut microbes, which then causes members of the population to die out and all of this sort of trading that the microbes are doing to break down, leaving only the self-sufficient survivors behind. Whether or not having only self-sufficient microbes in your gut then further causes a progression of the disease is another open question.
Chris - What do you think the implications of this are? It's academically fascinating and it gives us a different insight and a totally different angle on how we see these communities working together. But where do we go from here?
Now you've got this observation, what do we want to know next and how can we build on this?
Iva - Well, personally, I think that I guess the field should maybe try to shift away from finding, you know, the bad microbiome or trying to implicate in any possible way the microbiome as part of your cause of disease and instead focus on other potential causes of these conditions with complex etiologies. So looking for genetic markers rather than saying that the microbiome is the thing that is going to cause the disease and then potentially save us all. Because for instance, there's a lot of interest right now in people trying to create probiotic cocktails that could help treat somebody's gastrointestinal disorder. There's no guarantee that stuff like that would work if it's true that the microbiome is only reacting to a person having disease and not actually part of the cause.
17:16 - Queen ants do gene therapy to control their brood
Queen ants do gene therapy to control their brood
Laurent Keller, University of Lausanne
Who invented gene therapy? You’re probably scratching your head in search of the name of some or other biologist, but the answer is, it definitely wasn’t a human! Because, scientists have discovered that, by feeding pieces of genetic material called short RNA molecules to their nest mates, some ant species can use this “diet” to manipulate how these social insects produce a repertoire of different ants with a range of different appearances and roles - like workers, soldiers and queens - from just a single genome. As he explains to Chris Smith, Laurent Keller has been looking at harvester ants, which were either allowed or denied access to a specialised form of ant egg used as a foodstuff and known as “trophic eggs”. These are devoid of genomic DNA, so they’re reproductively inviable, but they are packed with calories and, as it turns out, pieces of genetic material that can be absorbed to alter gene expression and the development of the larvae that eat them…
Laurent - We were interested in understanding how there were variations in size between workers and ants. Typically, you can have smaller or larger workers, and we did cross-fostering experiments. And while doing these experiments, we found something bizarre, which was that when we did transfer and remove the trophic eggs, trophic eggs are a type of eggs without genetic information, which cannot develop, produced by queens or workers, and which were thought to be a source of food for the larvae and maybe the queens.
And so when we did transfer eggs between colonies, we found that when there were no trophic eggs, there were fewer queens produced in these colonies.
Chris - So just to summarise that for a minute then, so in an ant colony, you have queens that lay eggs, but also workers can lay eggs, and they can lay one form of egg, a trophic egg, which doesn't have any genetic material in it, so it's never going to turn into an ant. So it looks like an egg, behaves like an egg, but doesn't ever turn into anything, but they can eat it. And when they eat it, it appears to change the outcome for the ants.
Laurent - Exactly. But should we not explain that within the colonies, you have individuals, females, which can be different morphologically, like the queens and different types of workers, and that usually this is due to the environment. So depending on what is fed to the larvae, you have development of the larvae into a queen, a worker or a soldier, for example.
Chris - Do you therefore believe that there's something, some signal, which is embedded in those eggs, which is affecting the appearance or phenotype of the ants when they eat them?
Laurent - Yeah, it must be so, because in the trophic eggs, they look a bit the same as viable eggs, but their content is different. They have less food inside, which was surprising when we did analysis, than in viable eggs. And what we found on the contrast that there was more small RNA, so small RNAs are short pieces of genetic material, which have genetic information. And so there was more small RNAs and more long RNAs. And so this was quite surprising, because trophic eggs should not have more genetic information if it's just a source of food.
Chris - Do you believe then that those short pieces of genetic material are being absorbed into the ants that consume the trophic eggs and that they're influencing gene expression and therefore changing the appearance of the ants that consume the eggs?
Laurent - Yes, so small RNAs are known to be, easily go from the food to the body, and they can influence different things. So this has been shown in other contexts, that they can influence the development or the behaviour of organism. So it's very likely that small RNAs and long RNAs in trophic eggs influence the development of larvae.
Chris - So these ants are effectively doing gene therapy on their nest?
Laurent - Exactly, yes, they do so. And so the queens can modulate development of the other members in the colony. So whether larvae will develop into a queen or a worker by producing variable amounts of those trophic eggs.
Chris - Have you been able to prove that though? Can you show that these RNAs are functional, and when they go into the ant that consumes them, gene expression is modulated?
Laurent - No, that will be the next stage to be done, to really demonstrate mechanistically that those small RNAs, so we identify some of them, and now the next stage will be to inject small RNAs into larvae, and be able to manipulate development with only this factor being different between larvae.
Chris - But is the recipe for a trophic egg always the same? So if you take a trophic egg, is the different relative proportions of these short RNAs that do this manipulation, is it always the same? Or at different stages of the nest life cycle, do the relative levels get changed? So the queen can enrich for some of these signals and suppress others to change the outcome when the ants consume these eggs?
Laurent - This is a very good question. And we don't know. And it's true because now we know that trophic eggs can influence the development of larvae. One could imagine that queens could manipulate or influence the development of larvae or other things in the colonies in many ways by producing different types of trophic eggs. But this will be something to be studied.
Chris - It's extraordinary this because previously we thought this was all down to pheromones and secreted chemicals, didn't we? And so this is a really dramatic change to our view as to what might be going on.
Laurent - This is a strong belief, but nobody has identified those pheromones. The only thing which has been demonstrated is that the presence of the queens tend to suppress production of new queens. People have said it's pheromones, but there's not a single study which demonstrates that. So this is a strong belief in the field, which is based on no data.
Chris - So you might have a really disruptive discovery here?
Laurent - Yeah, I think so. And it's very likely, I think it's really worth to test our communities in other ant species and maybe other social insects.
24:05 - How cysticercosis leads to epileptic seizures
How cysticercosis leads to epileptic seizures
Hayley Tomes & Anja de Lange, University of Cape Town
One cause of the seizure condition epilepsy is the disease known as cysticercosis. This is the result of ingesting the eggs of the pork tapeworm, Taenia solium. These eggs hatch into larvae that migrate throughout the body forming tissue cysts, which often crop up in the brain, where they are known to trigger fits, although we weren’t sure exactly why. But now, thanks to Hayley Tomes and Anja de Lange, from the University of Cape Town, we have a clearer picture as to what might be going on. These cysts, it turns out, appear to be charged with the excitatory nerve transmitters glutamate and aspartate. And minced up and squirted onto brain cells, a “milk-shake”, as they dub it, of the cyst material triggers a frenzy of discharge activity. This would explain the link to epilepsy and also why, in patients with the problem, the fits seem to kick in after the cysts die off and presumably release their toxic cargo. Anja first…
Anja - So this parasite is called Taenia solium and it's basically a tapeworm, the kind of tapeworms you would think about living in your gut. The condition that we looked at is caused by the larval form of the tapeworm, so it's this like little fluid filled bubble basically with a little tapeworm head tucked inside the bubble and you get this crazy brain condition where these larvae develop in the brain and they cause these lesions and a lot of people who have these larvae in their brain end up having seizures. It's quite a common thing in certain parts of the world where you still have kind of free roaming pig farming.
Chris - These are pig tapeworms then and they get into the brain what? Because they're in the wrong host. If they find themselves in us they go wandering and instead of staying in the intestine they find themselves in the brain.
Anja - Yeah, we are the hosts for the adult tapeworm and they live in our guts. While those worms are living in our intestines they actually release a whole bunch of little eggs through our feces into the environment and then in areas where the hygiene isn't great, control in the environment isn't great, those little eggs end up getting into our food and we then end up eating these eggs. But you wouldn't see them, they're like very, very microscopically tiny.
But when we eat those little eggs they actually burrow through our stomach into our bloodstream and they circulate through our bodies and they kind of just go and sit in different tissues. But they seem to really like our brains and the crazy thing about these tapeworms is that they actually live there for an extended period like months or years quite happily and only when they kind of finally give up or the body's immune system finally attacks them or sees that there are some intruders, that's actually the stage at which the seizure onset happens.
Chris - So Hayley, do you get seizures because you have a physical entity sitting in your brain that shouldn't be there or is there something else going on where there's actually something more than a physical entity, it's maybe a chemical conversation between the larval form of the worm and the brain?
Hayley - That is the question because you can get seizures from traumatic brain injuries, from scar tissue, like you said, a sort of entity in the brain but you could be another reason and that's what we really wanted to find out. How do these tapeworms get into the brain, sit there silently for sometimes years, five, ten years in some cases and then suddenly seizures happen? That's what we set out to investigate.
Chris - How? What did you actually do to explore that?
Hayley - We did some electrophysiology, so looking at one neuron and sticking an electrode in that neuron while it's alive and recording how excited that neuron is, what is it saying, how is it communicating.
Chris - Specifically, are you talking about listening to a nerve cell that's right next door to one of these parasites so you can see if there's any influence of the parasite being there?
Hayley - We're actually specifically looking at the dead version of the larval parasite because that seems to be when the seizures develop, when it goes wrong. So I would have the worst day in the lab where I would make the tapeworm milkshake from all the larvae and essentially make this tapeworm juice which we would then spritz onto the cell body of the one cell that we were recording from in each instance and then we would watch the effect that that dead tapeworm would have on a single living neuron.
Chris - What effect does it have?
Hayley - Well, they get very, very excited. The first time I saw it in the lab was quite a moment, no idea what was going to happen, no one had ever looked with this technique at this kind of a thing and to just see that neuron spike, sort of fire off action potentials, communicate through electricity was quite remarkable.
Chris - Therefore, there's something in the milkshake, as you put it, when you grind up these larvae and you just put that onto the cells. I love the use of the word spritzing, it makes it sound much nicer than I'm sure it really is. But when it goes onto the cells, there's obviously something in there that's tickling the neurons. Do you know what is doing that?
Hayley - Yes, absolutely. And that was the finding. We knew that they were excited, now the hunt was on for what molecule in that tapeworm milkshake is having the effect.
And we did a bunch of experiments to determine that and we discovered that it is something called glutamate. Glutamate is an amino acid, but it is basically what our brains use for any excitatory signaling. If the tapeworm was releasing more glutamate or had glutamate in it, it was very likely then to be as excitable as we were seeing. So it all made sense when we got the answer of glutamate.
Chris - And Anja, why is the dead larva rammed full of glutamate?
Anja - It seems likely that it's kind of a byproduct of some metabolic process that they use. It could also be something that they're specifically producing in bigger amounts because we do actually see in some other brain pathologies, like brain cancers, those cancer cells produce a lot of glutamate because that kind of gets those neurons around them really excited. And when neurons get way too excited, they actually die off. And in cancer, it's kind of hypothesized that this is how the cancer cells make more room in the brain for them to grow into, which is something we suggested could also be true for the tapeworm larvae.
Chris - That is an interesting hypothesis. So you're saying that almost like the larva excites nerve cells to death to make space, but why would it do it when it's dead? And also, if it's dead, why does the epilepsy persist?
Is it because you've done damage to the brain by then?
Anja - Yeah, so they don't actually cause these seizures while they're alive, but we show in our paper that they do actually also release glutamate and aspartate while they're alive. So you would kind of expect seizures to be happening throughout the infection, but it only really happens when these larvae die. We think that it's because if you think about the size of these larvae, which can kind of be up to a couple of centimeters large, just the sheer volume of fluid that's inside that larvae and the amount of glutamate that must be in there is probably enough to push the brain over the edge. It's also true that you get a lot of inflammation when these larvae die. And we know that when there's inflammation in the brain, the brain gets less good at handling too much glutamate. We think that possibly that combination of already the brain not being too happy with having excess glutamate around and then together with just the sheer amount of glutamate that's probably coming out of that larvae upon death, I think that's why the seizures happen when the tapeworm dies. About 30% of people who have these tapeworm larvae in their brain and get seizures kind of continue to have seizures for quite a period of time. We think that that might be because our brains make scar tissue and then every couple of months or so, it goes back to that scar tissue and it tries to remodel it and kind of make it a little bit better. And each time that happens, there might be another exposure of some of the tapeworm elements and another kind of immune attack. But it's also possible that some of the people just have something that makes them a little bit more at risk of having seizures. And then once you kind of kick start that process, it kind of sustains itself.
33:22 - Fungal glucans reprogram an inflammatory state in sepsis
Fungal glucans reprogram an inflammatory state in sepsis
Maziar Divangahi, McGill University
Scientists in Canada have hit upon a new way in which severe systemic inflammation - states like sepsis - can lead to secondary, acute injury in the lungs; this is often a problem in patients being managed in intensive care settings, for instance. The findings hinge on a substance called beta glucan, which is released from the cell walls of fungi. Exposure at low levels, akin to the stimulus we all receive from the fungi naturally present within our microbiomes and environments, seems to be a good thing: it promotes a healthy immune tone that defends us better against a range of infectious threats. But higher level exposure seems to have the ability to reprogram a class of cells called alveolar macrophages, which normally sit quietly in the airways, mopping up inhaled debris and wannabe infective agents. Pre-stimulated by high levels of beta-glucan, though, these cells switch to a far more reactive state, which in the context of a severe inflammatory condition like sepsis, can lead to secondary devastating lung damage. As he explains to Chris Smith, Maziar Divangahi, from McGill University, has been wondering whether different levels of beta-glucan exposure could account for why some patients end up with this condition…
Maziar - We know that this fragment of fungi, which comes from the cell wall of the fungi, is able to benefit the host and enhance host defense against infection. But in this particular study that we did, and we were looking at the systemic inflammatory responses like sepsis model, we found that actually beta-glucan was not beneficial. And it was detrimental to the host immunity.
Chris - This sounds like it's contradicting itself. So can you just clear that up for me? Why, on the one hand, we've got something that appears to be quite useful, but can also be quite a pain?
Maziar - Yeah. The reasoning, it really depends on how we re-stimulate the immune system that has been already stimulated with the beta-glucan. So if it's too much inflammatory responses, then I think what would happen is that the beta-glucan will enhance these responses and under condition like sepsis that you want to dampen the inflammatory responses, then it becomes detrimental.
Chris - So the context matters then, is what you're saying? If we've got low grade exposure to this stuff, the kind of thing on a level that we would run into going about our lives healthily, it's a good thing having beta-glucan, this component of fungi, when they grow, they make it in their cell walls, don't they? The immune system is seeing that and that's translating into a good, well-modulated immune response. But when things get out of hand and there's inflammation and sepsis somewhere remote in the body, under those circumstances, the reaction to beta-glucan is quite different...
Maziar - Yeah. This is context dependent because it really also depends on type of the inflammatory responses you have. If you have a chronic bacterial infection, such as mycobacterium tuberculosis, or if you have immune response toward influenza, viral infection, these are very different kind of infectious diseases and beta-glucan in that respect is playing a beneficial role. But in terms of systemic inflammatory responses, like sepsis, that you have inflammation in multiple organs, beta-glucan is not certainly beneficial.
Chris - Talk us through then the experiments that you've done to test this out and show that that appears to be the case. How did you do it?
Maziar - So what we did, we used a mouse model of sepsis, a fragment called LPS, a gram-negative bacteria that has been clearly shown to really cause systemic inflammatory responses. We basically pre-treat that mouse with the beta-glucan and then after seven days, we induce sepsis by giving LPS.
Chris - When you say you pre-treat them with beta-glucan, what is that, by allowing them to be colonised with fungi or do you feed it to them? How are they exposed? What's the context there?
Maziar - In this case, we give beta-glucan intra-peritoneally because it goes systemically then. And then that will prime your immune system already with the beta-glucan, so your immune cells will be ready to react to the second stimuli, which in this case is the LPS. Because the magnitude of inflammatory responses is very big in LPS model, then of course your immune cells that have already been primed by beta-glucan will overreact to the LPS and it makes this whole entire systemic inflammatory response worse.
Chris - Which cells are particularly responsive to that beta-glucan? So when you put that exposure into the mouse and it goes systemically, which cells are seeing it and which cells are then changing their level of reactivity so that when the sepsis comes along subsequently, they're the ones that kick-start the process?
Maziar - In this model system, what we found is there are particular immune cells in your lung called alveolar macrophages. And because we are constantly exposed to the environment by breathing air, these cells are sitting in the lower part of the airway and they're responsible for reacting to pathogens or microbes or antigen that are coming into the lung and deal with them without causing inflammatory responses. So these alveolar macrophages appears to be really a major, they were the major cells that are overreacting now after beta-glucan treatment to LPS. And somehow these alveolar macrophages, we call it, they've been reprogrammed toward inflammatory macrophages and they are overreacting and then they ask for more immune cells to coming into the lung. And of course, then you have these massive inflammatory responses in the lung that causing enhanced the severity of the disease.
Chris - Why is the big question though, isn't it? Why should those cells respond in that way? Is this just basically a bastardization of a process that's supposed to be there, that's actually really useful, but then it gets carried away? Or is there something else going on that shouldn't, and this trips you over into a hyper-inflammed state under these abnormal conditions?
Maziar - Yeah. So these cells that are not inflammatory, somehow beta-glucan is able to change their phenotype and make them inflammatory. And now when you stimulate these cells, these cells that already inflammatory become hyper-inflammatory and detrimental.
Chris - Do you think this really happens in life like this though, because you've given very big doses of beta-glucan to your mice and then you're giving them a really profound immunological kick up the backside with the LPS. So is this just an artifact of a model or do you think in a person, this is really what's going on?
Maziar - Fungi are part of a microbiome and they are really important for regulating our immune system. So one hypothesis that we have is that because of that, we have certain level of the beta-glucan in circulation. So most likely the level of the beta-glucan that you have in your circulation, or I do have in my circulation in Canada, is very different than the level that people leave in India or other countries. So does this make a difference? As I mentioned, beta-glucan could be beneficial against certain infectious diseases, but in this case is detrimental. So the reasoning that people will develop sepsis, is that related to the level of the beta-glucan in their circulation? And we would like to know if this has anything to do with this overreacting of immune response under those conditions.
Comments
Add a comment