Professor, Integrated Department of Immunology, National Jewish Health, Denver, Colorado; Distinguished Professor, University of Colorado Health Sciences Center David X. Tejada
DAVID X. TEJADA
Sometimes the experimental controls spit out the most interesting results. In the early 1980s, Philippa “Pippa” Marrack and her lab partner (and husband) John Kappler were investigating how, exactly, macrophages process antigens so they can be recognized by T cells. “We knew that macrophages have to chew antigens up into little pieces before the T cell can see them,” says Marrack. “The question was: ‘what’s special about the way that macrophages are doing this chewing?’ ” So a student in the lab served macrophages some ovalbumin to munch. As a control, he cut up the same protein using trypsin—a digestive enzyme that dices proteins into pieces. To his surprise, the trypsin-minced material “worked like crazy,” says Marrack. It turned on T cells as well as the protein that had been worked over by macrophages. “That was a profound observation, actually,” says Marrack. “It told us that all you have to do is chop an antigen up into little bits and it’s going to be seen by the T cell. Now we know it’s because the antigen has to bind in the groove of an MHC.”
That kind of unexpected find, Marrack says, “can be the most marvelous thing, because mostly we do experiments to confirm what we already know. But when you discover something you didn’t know was there, well, that’s like Columbus bumping into America.”
During her career as an immunologist, Marrack has bumped into all sorts of amazing results, from her early finding that T cells and B cells “see” antigens differently to her 1983 discovery, made with Kappler, of the T-cell receptor that actually recognizes antigenic peptides bound to a major histocompatibility complex (MHC) molecule. Here she shares her tales of adventure, which include selecting a handsome advisor, refusing to stay in the kitchen, and thinking like a Martian.
MARRACK ON THE MARCH
Fateful attraction. Marrack was drawn to her PhD advisor, Alan Munro, by more than his expertise in immunology. “He was a good-looking guy,” she laughs. “That’s frighteningly un-PC. But let’s not pretend that sex doesn’t have something to do with the decisions we make.” Working with Munro at the Medical Research Council (MRC) in Cambridge, England, Marrack set up a culture system in which they demonstrated that “if you want B cells to make antibodies, you need to have T cells there,” she says. “We went on to show that T cells don’t see antigens in the same way as B cells do. If you take a B cell that has antibodies against sheep red blood cells sticking out of its surface, and you mix it with sheep red blood cells, it’ll make a thing that looks like a raspberry, with the B cell in the middle and all these red blood cells stuck around its outside. It’s called a rosette. If you do the same thing with T cells, you don’t get any rosettes. So we concluded that there was something different about the way T cells see antigens.”
“When you discover something you didn’t know was there, well, that’s like Columbus bumping into America.”
Fusion power. As a postdoc at the University of California, San Diego, Marrack isolated cell fractions that could replace T cells in stimulating B cells to produce antibodies. She then joined forces with fellow postdoc Kappler and headed to the University of Rochester in New York. There the couple showed that helper T cells, like cytotoxic T cells, recognize antigens bound to class II MHC molecules—work published in Nature in 1976. But it wasn’t until the two moved to Denver three years later, accepting dual positions at the University of Colorado Health Sciences Center and National Jewish Health, that they discovered the T-cell receptor—the protein responsible for recognizing the antigen-MHC complex.
“Our technician had gone to a workshop at a Keystone conference,” she says. “He was fed up with killing mice to make these supernatants that could stimulate B cells in place of T cells. So he came back to lab saying, ‘Why don’t we make immortal T-cell hybridomas that will make this stuff for us?’” So they fused a T cell with a tumor cell and got—disappointed. The cells did not produce the stimulatory cytokines they were seeking. “Then we dumped in some concanavalin A, which stimulates T cells, and, lo and behold, these cells made tons of stuff.”
But ConA, a protein that binds to a variety of cell-surface carbohydrates, broadly activates all T cells. Marrack and Kappler wanted something more precise. “John thought, what if we made a T-cell hybridoma from an antigen-specific T cell? Then you could stimulate [the hybridoma] with that specific antigen.” Those cells would also have, on their surface, a receptor that recognized that one specific antigen. “So we thought, ‘We’ll start immunizing mice with these hybridomas and eventually they’ll make an antibody to the T-cell receptor. Which they did. Once we got ourselves an antireceptor antibody, we could isolate the T-cell receptor.” In 1983, they succeeded—at the same time, more or less, as groups led by Ellis Reinherz and Jim Allison. “Our discoveries, though, got completely swamped out by Mark Davis, Steve Hedrick, and Tak Mak’s discovery of the T-cell receptor gene, which actually was published about a year later. But there you go. That’s life.”
The trouble with X. Marrack has started looking into why women are more susceptible to many autoimmune diseases than men. “The emphasis of genome-wide association studies has been on polymorphisms: can we look at people who have lupus and find they have a particular polymorphism that distinguishes them from people who don’t have lupus? Well, I thought, the X chromosome is the most common polymorphism in the population. So maybe there’s something intrinsically different about the immune systems of men and women—or male and female mice. We discovered that old female mice all have a collection of B cells not present in young mice or in old males. And when you stimulate these cells, they make autoantibodies against chromatin.” In mice, the proliferation of these B cells depends on a Toll-like receptor protein called Tlr7—which is encoded by a gene on the X chromosome. Marrack and her colleagues have found the same autoantibody-producing B cells in elderly women with rheumatoid arthritis or scleroderma, a finding they’re continuing to pursue.
Fishy finds? In trying to understand why T cells are so attracted to MHCs, Marrack and Kappler are examining the interactions between the T-cell receptors and MHC molecules from one of our most distant relatives. “The cafeteria was frying up some trout for lunch one day, so our graduate student, James Scott Brown, popped down and asked the chef for a chunk,” says Marrack. “The gene for the fish T-cell receptor was known, so we used the raw trout to PCR it out. We’re just writing the paper now. We should probably add the chef.”
ON MARRACK’S MIND
Table talk. Marrack did her graduate work at MRC in the late ’60s. “At the time, it was fairly isolated, so we all had to eat in the cafeteria: coffee in the morning, lunch in the afternoon, and tea at 4 o’clock. There were these large tables where you could seat 8 people. So you could wind up sitting next to anybody: Francis Crick or the guy who swept the floors. That led to some very stimulating conversations. It sounds silly, but if the tables are small, you can go to the cafeteria with one or two people from your lab and you’ll all sit together. But you’re unlikely to troop in with 7 colleagues. So if the table seats 8, you’re more likely to have a chance encounter.”
“I tell women, if you want to succeed, pretend you’re a Martian. And then behave as you see fit. Don’t be bound by convention.”
Alien behavior. “As a foreign woman in the States, you can get away with a lot more than you can in your own country. That’s because you can pretend that you don’t know any of the rules. For example, I was at UCSD, and at the last minute instead of going back to Cambridge, I went to the University of Rochester with my now husband. There wasn’t a job for me there and I became his technician for a brief time. I think back in England, I would have been more stereotyped and less able to get away with that. If a woman shows up, not even married to a guy, and she’s working as his technician, the expectation is she’s going to continue being his technician and everybody’s going to think of her a sidekick for the rest of her life. But somehow, not being an American, I was able to ignore those expectations. So I tell women, if you want to succeed, pretend you’re a Martian. Pretend you don’t come from this place. And then behave as you see fit. Don’t be bound by convention.
Gut feelings. “I was supposed to go back to Cambridge. I had a job and a grant and everything. But at the last minute, I left my [first] husband and followed John to Rochester. So I left my husband, my country, and a job, to go to a place I’d never been to with a guy I didn’t know very well. And it all worked out fine. I think you should always follow your heart. Actually it’s really in your stomach where the feeling occurs. I think good decisions are made in your stomach and then afterward you rationalize that they were good decisions in your brain.”
Take the techs. “It’s always been our practice to take our lab techs to meetings. Technicians are the lifeblood of the lab. They work as hard as anybody else, and they can come back to lab with good ideas, so why not? It works to our advantage and it just seems like the right thing to do.”
Data matters. “As a scientist, you can’t be overconfident and too attached to your theories. If you do an experiment that shows that what you believe is wrong, you have to be prepared to dump your idea. I think John Maddox once wrote that the problem with biologists is that they’re obsessed with data. Well, that may be what John Maddox, a physicist, thought. But you just cannot ignore the data, however convinced you are about your idea.”
Detrimental supplements. “If you go back and look at Nature from the early ’70s, you could publish a paper that had one figure in it, maybe two. Now papers have four figures and 25 supplemental pieces of data. That’s because we have so many more tools in our toolbox. So reviewers can go on asking you forever to do additional experiments to show the same thing. All you’re really doing is wasting a year in a postdoc’s life and spending the public’s money, just to prove—using yet another tool—something you already knew.” Know your delta Gs. “People come into biology thinking they don’t have to know any chemistry. And that’s not true. Because we are a bunch of chemicals. Sure, it’s easier to do biology than to understand thermodynamics. But that’s how your body works. So you’d better get a feel for it.”
THE INNER MARRACK
Lab partners. “My husband and I started working together by compulsion, because there wasn’t anyplace else for me to work. And it turned out very well. In fact, the only thing about our marriage that has always worked has been the lab. Every marriage has its ups and downs, but our lab work and the science have always gone extremely well. We’ve been very lucky in that regard.”
No regrets. “Sociologists will tell you that when people make decisions, the harder the decision was, the more committed they are to it afterwards. So I don’t think at any time I’ve made a wrong decision. That sounds awfully egotistical. But there’s nothing about my life I regret. I feel guilty about some things: there are people in the lab I haven’t taken care of as well as I should have because I was too busy. So I feel a fair amount of guilt. But not regret.”
A woman’s place? “At the beginning of my career, chairpersons told me I should be behind the kitchen sink. That came up several times, actually. When we went to Rochester, for example, I was a technician, but I was teaching this immunology course for the biology department. When I applied for a faculty position in the department, the chair at the time said exactly that. That I should be behind the kitchen sink. Of course I paid no attention.”
Tickling the ivories. “There’s something very tactile about just touching a piano key. It’s marvelous. Now I’m learning a little Scriabin and some Bach. The pieces are not that easy to listen to, but they’re tremendously satisfying to play. Scriabin is all about the chords, so there are no tunes you can go away and hum. But I love playing, even though I’m fairly hopeless at it.”
All in the family. “If you ask whether I neglected my family because I worked in lab, I did. But the kids don’t seem to resent it. My parents were a tremendous help. They believed that a family should take care of its own—and everybody else’s. All the kids in the neighborhood would show up to spend time with their ‘pseudograndparents.’ And when my parents got sick, we worked hard to look after them. After they died, my husband and I had a sense of satisfaction that we had done what we could for them. And they were satisfied, too, that they had done what they could for us, for the kids. Which is how families should operate, in my opinion.”
Graceful exits. “My husband has an excellent exit strategy. He builds and repairs guitars. So when he decides he doesn’t want to do science anymore, he can go off and do that. I have the grandchildren. That’s the classic ‘out’ for women, isn’t it? Like all grandmothers, I dote on them. But in the end I think the decision to retire might be made for us. When we don’t have any more grant money, I think we’ll have to get out. Because if we don’t get funded, presumably it will be because people don’t think we’re doing anything useful anymore. So I suppose that would be the signal.”