Scientist Stories: Gwendalyn Randolph, Peritoneal Macrophages

This is a special episode of the Immunology Podcast, AAI 2022, Peritoneal Macrophages with Dr. Gwendolyn Randolph. Hey everyone, this is Dr. Jason Goldsmith and Dr. Brenda Raud. Welcome back to the Immunology Podcast where you have conversations with immunologists. This week we're bringing you 3 very special episodes of the Immunology Podcast straight from the American Association of Immunologists annual meeting. Immunology 2022. Today we'll be chatting with Dr. Gwendolyn Randolph from Washington University in St. Louis to discuss her talk on the diversity, function, and mysteries of peritoneal macrophages. But before we get to that—

Whether you're looking to attend an immunology conference this year or to expand your network, make the most of your experience by downloading our collection of tools to help you prepare to your next event. Stem Cell Technology's downloadable checklists and guides include recommendations on how to get ready before attending conferences, tips for networking, best practices for your LinkedIn profile, and more. Download the conference toolkit at www.stemcel.com/conference-toolkit.

All right. It's time, folks.

That time of the year. The most magical immunological time of the year. Very exciting. Huge, huge deal. Finally, AI meeting in person again this year in your favorite city of Portland.

It is the best city.

And so we're super lucky that we're going to be speaking to some of the participants of AAI, some people presenting, representing the finest of the finest. And today, who are we talking to today, Jason?

It's Gwendolyn Randolph. So we got, we got a whole cohort coming up here. So this is going to be good, good times. And we'll be getting to her right here in just a second.

But before that, let's not forget that the audience can follow us and the updates from AAI on the Immunology Podcast Twitter feed.

Yep. We are going to tweet the heck out of it for you guys.

Continuing today with our AAI-themed episode, after also talking to Dr. Gary Koretsky, the president of the AAI for this term, we have a very special guest. Joining us is Dr. Gwendolyn Randolph, She is a Emil Unanue Distinguished Professor at the Department of Immunology and Pathology at Washington University in St. Louis, and is going to be talking to us about her research on macrophages and also some very special activities that she's taking part of during AAI this year. Dr. Randolph, thank you so much for joining us.

Thank you so much for inviting me to be a guest on this program. It's a real privilege.

You are presenting, as I mentioned, two times. You're going to be part of two different talks this session, in this program. And you have one talk on Saturday at 8:00 AM. So hopefully the hardcore immunologists will be there. Diversity, Function, and Mysteries of Peritoneal Macrophages is the title of your talk. But you're You're also going to be part of the careers in science lecture and roundtables that are taking part on Sunday at 12:30 PM, and where you're going to be talking about becoming a confident scientist and embracing your authentic self. So I'm very excited to talk about both of these events, but why don't we start with the macrophages?

You've done some really cool work. I think some of your most recent stuff has been in liver biology and the role of HDL there, and then some of this overlay with macrophages there, which obviously are important in lipid metabolism generally. So could you give us the lowdown, the CliffsNotes version on that for some people who haven't read it?

The lowdown really of the connection between, you know, how are we talking about HDL and the liver and trafficking of HDL is my My interest in macrophage biology got started because I was working on monocytes for many years. And I was interested in the trafficking of monocyte-derived cells and how that trafficking related to whether they became macrophages or dendritic cells. Turns out dendritic cells, of course, are a lot more prone to trafficking than macrophages. But that trafficking question is something that really still underlies a lot of what we do, even though macrophages tend to kind of stay in place and do their job locally.

I'm glad you mentioned that because many of our listeners might not know that you were one of the first to describe the differentiation of macrophages from monocytes, actually working in Ralph Steinman's lab 30 years ago. And since then, also, our understanding of the origins of macrophages have very much changed. And I think that's very— also very— was a very important piece of— in the puzzle of macrophage and identity. But our understanding of the identity of macrophages has changed a lot.

Oh, absolutely. And really, when I was working with Dr. Steinmann, I was describing monocytes becoming dendritic cells or taking on a lot of dendritic cell properties. And what I was going for was trying to understand if a monocyte derived cell, which I assumed would become a macrophage, that was a dogma in the field, would it ever leave a tissue and go from that tissue to maybe another organ? And so that organ-to-organ crosstalk, which we just published on and have linked HDL to in turn and talking to liver macrophages, is, you know, something that really goes back for me a few decades to the beginning of my career. And so I think at that time we we thought all macrophages in all organs were very similar and all came from monocytes. So you're right. Now, in the last 15 years or so, we have come to understand that tissue macrophages, resident macrophages in organs, often derive from embryonic sources. And a macrophage is not a macrophage is not a macrophage, even though, of course, they share common features across. Organs and, you know, still defining their name as macrophages.

So the phage function is what makes me think is the linkage to the lipids. So can you kind of tie in— so a lot of your work looks at lipid, the effects of lipid metabolism, lipoprotein, so LPS being kind of carried along, trafficking. What is it about a macrophage that makes it drawn to lipids, maybe, and what is it that those— and what's the consequence of that in terms of its behavior?

So a couple of things. There are many things that are still not known. We do think of macrophages as a cell type that can load up with lipids quite readily. And so sometimes you hear them called foam cells, and we've appreciated that occurs in atherosclerosis, but now we see it more and more in many other scenarios, both pathological and I would say even homeostatic. One of the key features, of course, is that macrophages express a wide variety of receptors that allow for uptake of lipids in their oxidized form. And lipids, of course, are often carried in particle form. And there's proteins and lipids that can become oxidized. So the scavenger receptors are perfect for that. And specific receptors to take up certain proteins on those lipoprotein particles. But macrophages are also incredibly endocytic. So you get a third mechanism by which engulfment is going to be very prominent. Now, processing those lipids is connected, of course, to their ability to process lipids in a cell they might take up, a dying cell. And so being able to handle that is core to the macrophage metabolic function. But I also think that macrophages are often storing lipids actually to protect the microenvironment from lipid toxicity. So I'm starting to see in datasets, including datasets with some collaborators here at WashU, that dendritic cells are actually really good at synthesizing cholesterol. And it seems like macrophages are better at storing cholesterol. In the field, we think that part of that storage is, in fact, protection. So a few years ago, we thought of the foam cell as the pro-inflammatory type of macrophage. But I think now there's a huge amount of evidence that cell is a cell that's really setting up to stop inflammation or quell it or maybe even promote anti-inflammatory functions.

So then the LPS story is interesting to me just because LPS is a big bugaboo that causes lots of damage. And I've seen in other fields the role like LPS being a bystander. And so bacteria that process other things in the gut pull in LPS. It goes around and I've seen other talks even at other meetings recently that this LPS lipid cholesterol link. So could you kind of give the high level, like, what about the liver?

Absolutely. So I haven't really actually mentioned the specific link that you're referring to just yet, but we have known since the mid-'90s, actually going back to my postdoc days, even work that was going on at Rockefeller while I was there as a postdoc in other labs, were showing that LPS could become incorporated into lipoprotein particles. So it's been thought for a while that this could have a neutralizing effect just by, you know, the LPS being part of the particle and kind of kept out of other spaces. But what we discovered is that a specific type of HDL actually carries along with it proteins like LBP, or LPS-binding protein, that appears to hide its ability to bind to TLR4, which of course is highly expressed on macrophages. In fact, in the in-gen profiling network that we published about 10 years ago, we found that TLR4 was a key core signature gene that identified macrophages. So what we have discovered is that the intestine specifically secretes the type of HDL that will neutralize LPS such that when the LPS arrives to the liver downstream of the intestine through the portal vein, that actually these macrophages can't even see it. See it. We also found though that this HDL can hand off this LPS to other enzymes that will eventually detoxify the LPS, but the macrophage can't react because it doesn't bind.

I find it very interesting, this dichotomy between macrophages having a pro-inflammatory and an anti-inflammatory role to play. And how, for example, you already mentioned the case of cardiovascular disease, atherosclerosis, usually macrophages are seen as this problematic cell type. But then in many other aspects, macrophages are crucial. In the case also of lipids, what is our current understanding? Is there more nuance to that when you say macrophage? Because you have a lot of experience understanding atherosclerosis and the function of macrophages in this context. Is it more nuance that we are seeing now that we didn't know before?

Oh, I think we're just at the tip of the iceberg. That, you know, the idea of putting macrophages into categories is not incorrect. It's actually really helpful constructs to the field, and you can find macrophages under, uh, in these categories, but we still don't completely understand the details behind how macrophages bring about so many different functions and outcomes. As well as we're starting to really understand that, you know, a few categories is not enough. You know, that macrophages play roles and have phenotypes that in the same tissue are parsing out really different functions. So I could go into atherosclerotic plaques and give you my view of, you know, a monocyte coming in. What we think now is that monocytes come in and find themselves in an environment where, as they're differentiating, they may be more prone to being pro-inflammatory, which also has certain benefits to setting up a healing response, whereas other macrophages, and perhaps this includes the foam cell, you know, are not necessarily, you know, driving that response, maybe even more resembling the tissue macrophage that is very quiet and anti-inflammatory. But I absolutely guarantee you that not everyone will agree with me on that. And so there's still so much work to do.

I want to ask a question that arises a lot of eyebrows often, especially lately. What about M1 and M2 macrophages? What is your position against this particular classif— or regarding this particular classification?

I think the classification itself, again, is beneficial. It helps orient especially newcomers to the area. It helps you get a feeling of a research direction and maybe how to begin to look at your data. However, there is a lot of misconception around it. For example, Often it is thought that a macrophage is in one of these states or the other. I agree that the states exist, but they are not really— and even the concept of a spectrum between the states is not quite correct. There are so many scenarios, and I would argue that many resident macrophages in the homeostatic state are not even really close to either one. Now, there are some resident macrophages that look a lot like an M2 type of macrophage, But often they are not that. So my recommendation is to go in with— to a tissue and ask, what is the resident macrophage in that tissue? What are its characteristics? And have no intent to try to classify that cell as an M1 or M2. Now, as one is, you know, going through data and watching what happens, say, you know, after a stimulation or a pathological scenario, you may find that a trend exists. And then it's it's useful to use this term. But it is far too simple and often used as a default. I need to figure if this cell is M1 or M2, or I need to try to make it be an M1 or M2 to control the situation. I don't think that's useful because it is too oversimplified and just simply not correct. So I'm not totally against the terminology, but And we still even pay close attention to it. It just falls short of the full story.

So as a follow-up then, if we want to go in with open eyes, but everyone does flow, right? And tries to figure out, oh, what cells are in here? What do you think then is the bare minimum definition, flow markers, single-cell RNA-seq, I don't care, that it's a macrophage so that we're talking about what the macrophage does?

Again, you know, if you get down to flow markers, you know, maybe one shouldn't get down to flow markers, but flow, you know, flow markers, gene expression profiling, they're quite related. I think they're useful. Back in the days of dendritic cell biology, we used to talk about functional definitions. I like molecular definitions. And I would still argue that we know some key signature genes that are defining macrophages. And we've argued that in flow cytometry, the really great choice would be Fc gamma R1, you know, a clear function of Fc IgG binding of macrophages. And it looks like in profiling that it's a really useful marker for macrophages together— together, I underscore that— with a few other genes. And those other genes can be MCS receptor, which of course is really driving the identity and survival of many macrophages, or some receptors like myr tyrosine kinase. Now the problem with both MCSF receptor, sometimes referred to as CD115, and MRTK, is that they're ADAM17 targets. So they're shed by this protease, sometimes in the preparation of the tissue or in the context of inflammation. So, you know, you do have to be a bit flexible considering your situation when you're setting up a way to find a macrophage. But those 3 markers, you know, combined, I think are really great starting points. And they all touch on different functions of the macrophage. Now, what I would argue that one does is go into a tissue to find the most prominent, most quantitatively prominent, and, you know, perhaps already well-known macrophage in that particular organ. And, you know, classify that as the tissue macrophage. Very often that will be an embryonically derived resident macrophage. And then look for the additional resident macrophages, which are going to be a smaller population. And some of those, for example, will be the perivascular macrophages or the surface-covering macrophages seen essentially on the surface of many organs. Some of those express Lyve1, a hyaluronan receptor. And so they should be counted among the resident macrophages. Although again, quantitatively not as huge. And then after that, think about what are the macrophages that might occur either as a process of recruitment from monocytes or perhaps at new differentiation states that would occur after a tissue perturbation. So those kind of 3 tiers are how we view the macrophages. And all the while, we're trying to find the dendritic cells in that tissue because there should be some. And, you know, the undifferentiated monocytes. So we usually start with the macrophages and then kind of, you know, try to find all these different populations and sort through it.

So very good guide to everyone looking into macrophages and their complexities. And it's important to have, I would say, a starting point, a reference, a good frame of reference to study them properly. Otherwise you get lost in all the details and all the little subpopulations, the little things that— and I think that's also the case for so many immune cells, that often we get so drawn into the subpopulations and we forget to focus on the function and on the things that makes them belong to this particular cell group. I think it would be nice to also, as I mentioned, talk about your other point of participation in immunology this year. You have been— you are an advocate, or you're very— you have been very vocal over the importance of equal opportunities for women in science, and I think that is very admirable. And you are now also joining the discussion with your presentation on becoming a confident scientist and embracing your authentic self. So I was hoping that— I know, we know people will have to go and see it to know, but whether you can share with us a little primer, or you can maybe talk to us about what is that you will be discussing, why people should join, and what would you like participants to take from this roundtable and these lectures?

You know, I think it's a challenging one in the sense that I don't have all the answers, and some of what I will be sharing will be my own personal experience, and I'm an N of 1, so, but I want to, I think a major takeaway will be why not try, as either a young scientist, you know, who I assume will be attending, as well as maybe other people at different points in their career, why not try to organize your career in the way you want it to be? I feel like it's a simple but important message because you often meet people who feel like they have to hit certain features, certain accomplishments, or conform to certain approaches or even topics to find the career path that they want, for example, a career path in academia. And, you know, I don't think that's true. It might be surprising to some that I used to be actually, I would say, somewhat shy and not confident. But one of the things I've learned and began to really appreciate even more in practice over time is that it doesn't hurt to try it your way, which is not to say that you don't listen to, you other people's perspectives. In fact, very much you should, and also, you know, keep taking stock and attempting to improve yourself. But to, you know, to generate a career in the way that you want it on your terms, I actually do think it's worth trying. You know, the thing is, if it doesn't work out that way, you're still going to be super marketable, so just give it a shot. And, you know, if you're curious, I think some of the elements like, for example, women and how to work-life balance, if we want to use that term, it can be tricky to think that you can't make it happen your way. But I decided at some point in my life, I'm going to give it a shot. It's not perfect every day, but I think it's possible.

So you brought up— I read one of your articles about— you'd done in JEM. Last year. And it made me want to ask, so when I think about it, one of them is the child-rearing, child-bearing, like, like that extra hurdle which disproportionately falls on women. And so you make a point though that obviously women are not a monolith and that's not true of all women. And so how do you think you parse out those— that issue? Because on one hand I've seen, you know, some data and it looks like it's pretty good that if you just give writ large parental leave, doesn't— man, male, woman, doesn't matter— if you have a strong parental leave program that not only supports women but supports the partners of women, which then support the women getting back, because then the spouse could take off. If the spouse has one week off, they can't help. They can't— you can't share the burden. And so I see that as a component. But you also then identify that, well, that you can't just do that. And so I was wondering how you kind of, if you, if you had to think of it as a mixed model, right? There's all these factors. How do you parse that out? Or how do you, what dials do you go after? Obviously try to, you want to fix it. Do you fix everything at once? Do you go hard in the paint on the parental question because it's such an issue? And then you also look at other structural issues about just treating people with respect. Like, like how do you parse the whole picture in, in chunkable bits?

Well, so that's a good question. And you know, there's still a lot of work to do. I'm not sure I have all the answers, but I think one of the things that you do is you find a committed leadership who is really willing to have a multi-pronged approach that happens simultaneously. And I'm not sure, I think one fear is that it's a really expensive approach, but I'm not sure that that's necessarily true. And again, if we push this mindset of let people try to promote their careers and parse their time in a way that makes sense to them, you know, that might mean that you need to provide, you know, opportunities, you know, on-site childcare is an amazing discussion that is expensive and in some cases, you know, hard to do. I just think that there's a lot of creative ways in which we can move forward. Actually, this week I saw a post on Twitter where a mom, a new mom, was just saying all these wonderful things about her baby. And then she said her baby's doing really well and that she's bored. She wishes that she could talk to her lab. But she's in a country where it's expected that she has this incredibly generous childcare and she's supposed to stay home for 4 and a half months before her partner kicks in and helps out. And again, that's confining. And so, you know, the advice that she was giving, most of the comments were just do it your way. It's okay. It's not— you shouldn't feel bad as a mom, you know, for wanting to do that. And so I just, you know, I'm looking for that type of freedom. Again, it doesn't have to be around childbearing, but that type of freedom and trust. It's institutional trust, uh, is, you know, incredibly valuable. And it really, really means that the leadership has to trust that it's going to work.

That's, that's a tough one. I, I agree 100% that you need the right leadership and you need the, the weight of the institution behind this, this acceptance that people are people and you need to give them the opportunity of balancing their life and their career. And I think women are particularly— it's particularly hard to do that. But, and don't— I think not being too paternalistic in the way that telling you, you should do this, rather than you, you are free to do— this is the safety net that we give you so you can, um, you have the opportunity to navigate in your own path. And I think that's really, really important. Our listeners who are attending will be looking forward to attending your talk and hearing more about this. And I think I'm just saying regarding the whole session, I've been looking into all of the session that, I think it's in this career science, in science lecture roundtables. I think also AI has made a real effort in bringing all this different perspectives and different resources to the participants. And I think that's really nice. I'm not sure if this is a recent addition. I'm not familiar with the last AAI program, but this seems very progressive in general. It's very nice.

Yeah, I do feel like AAI has been on the forefront of constantly adding venues that allow people to discuss the things that are really critical in the field. And there was a time when these issues weren't discussed, that there was a plan and, you know, or just an expectation of how things would be, and, and we didn't talk about them. I do want to say one thing I think that is missing from the article that I wrote that I wish I had added would relate to salary and equal pay for equal work kind of concept. And I think recently I was talking to faculty at various places, and I've seen this over the years, that when people get promoted, oftentimes they're told that their salary increase associated with promotion will be a certain percentage increase to their salary, and that is a huge problem, and I'm really active about fighting it, Because what it implies is that if— and we often see this in women and people of color, and this was true for myself, you know, starting off, you may actually not have the confidence. So to bring it back to confidence, you may not have the confidence to ask for the salary that you want. And to be frank, you may not get— it may not be a positive outcome if you do ask for the salary you deserve at that early stage in your career. So then to say that promotion as a percentage increase keeps you in that underpaid status and actually it grows on a dollar scale over time. Yet our institutions who, you know, keep giving reports about salary and, you know, their progress to equal pay are still using that as an approach to promotion. I really want to see to that change.

So it's interesting. So I, I work in industry, and when someone gets promoted, and every year your salary is evaluated to make sure it compares to the market. So sometimes, you know, like a base percentage is a percent, but if you're way off because the person under-negotiated and you're recognized as valuable talent, you just get an adjustment. And when you get promoted, it's a number not like a percent. Now, we tell you what that is in terms of percent because people do that, but it's like, here's your new number for your new level. And it creates a way to kind of fix mistakes of negotiation in the past naturally.

I completely agree. That's exactly what I want to say. There should be benchmarks for every, you know, promotion point so that if you somehow started off falling short of that benchmark, But what I have seen is actually the calculation of your present salary. I do think that there is, you know, effort to look at salary structures to see if there are individuals who are particularly off the norm, but in many places, especially places where salaries are not, you know, reported, most people have no idea really what those norms are. I have to say I don't know what the norm is for my current institution, and so, you know, it's also private, so that again, this is why I think that it should, this should be actually openly discussed, and leadership once again should come out and say, okay, you know, the starting salary for this particular position, you know, we'll move you up to that, and it is X. Rather than say, you know, it's going to be a percent increase.

It feels like academia is one of those industries in which you're allowed— because I think academics in general, we don't feel like talking about money, so that allows the system to be very opaque. I think many other industries could not afford to have such opacity because people would not sign up for their jobs, in a way. But I think that was a very interesting food for thought, being aware of those issues, and hopefully change will come, especially with people like you being vocal about it. I think bringing the conversation to the table, I think, is really valuable. In the name of the women in science, I appreciate your contributions to that too. I think that with this, we can maybe just start finishing up our conversation. So as part of our round— the rounding up of our episodes, we'd like to inquire with our guests something about themselves that is not necessarily science-related. So I guess a question that we have for you is that if you were not a successful immunologist, what do you think would be you would be?

So I would be a farmer. So I love— I grew up on a farm. I wouldn't be the farmer of the farm I grew up on, but I really love— I love farming. So sometimes I still think— and you know what I realize, it's sort of a joke, but one of the things that gave me confidence to try the areas of science that we worked on and even to follow my passion rather than to follow the, you know, the trend at the time was this like feeling, well, I could always go back to the farm. And in a way I couldn't because I was a girl and in my culture growing up, girls didn't become farmers, they just married farmers. But nonetheless, that's what I would do. And so I know it's kind of funny. I also have this fun video from where I grew up of a crop sprayer, and it's just like, I guy who's like getting really low and like, you know, putting fertilizer down on the crop. And it's so— to me, it's actually inspiring. So sometimes in my office I watch it because it's crazy. It's a bit dangerous, but it reminds me of the risk-taking that is both actually real in any career like science, as well as what must be the true exhilaration of 60.

All right, okay. I also think that in a way farmers are also a little bit science— scientific in the way, you know, having to grow their crops and methodically take care of their farms. It's also, I think, an interesting— can be an interesting intellectual endeavor as well.

So for sure, I mean, I'm doing— I do have a small vegetable garden in my backyard and I really enjoy it, but every years of experiment, right? And when you finally learn why certain things are failing, but it takes a whole year to do the experiment, and then you have to replicate it, and sometimes it doesn't work.

Well, it was such a pleasure talking to you. Uh, so I wish you success in your, in your lectures at AAI and getting to meet, uh, all the— everyone back in person. I think— hope you're very excited. Uh, I also also, like we are, about having these in-person conferences again?

Absolutely.

I'm looking forward to seeing you and so many friends and meet new people at AI.

Thank you for joining.

This brings us to the end of our show. Don't forget to subscribe to our newsletter at www.immunologypodcast.com to get the show notes, including an episode summary and links to all the interview and roundup papers. You can also reach out to us on Twitter at @ImmunologyPodcast. Immunopodcast or by email at info@immunologypodcast.com with feedback or to suggest guests. See you next time.