Profile: Professor Dan Davis - Capturing the killer cells
Professor Dan Davis has spent most of his career using microscopes to watch immune cells detect and kill diseased cells. From unravelling cell communication to popularising gene research, the world-leading immunologist tells Microscopy and Analysis how it's all happened.
Professor Dan Davis has pioneered the use of novel imaging techniques to visualise key molecular components of the immune response. This year, he published his popular science book, 'The Compatibility Gene'.
Dan Davis never set out to study immunology. In fact, on leaving school, he didn't even want to be a biologist.
Instead, Physics was his chosen degree, and on graduating from the University of Manchester with a First Class Hons, he headed up to Strathclyde University to study for his PhD in Physics. But on finishing his doctorate, Davis switched disciplines.
"I changed my mind. I started to think life was a fundamentally interesting thing to study and I could make a bigger contribution to science by studying the human body rather than the area of physics I was involved in," he says. "I felt the revolutions would be happening in biology and that's where I should be."
At the same time, Davis also wanted to work in the US. As he puts it, he figured this would be the most exciting place to study, so he started writing letters.
"I just wrote to random people doing amazing science in prestigious institutes," he says. "I wrote to researchers in all different areas of biology, including immunology."
Many replies later, Davis accepted a postdoctoral research position in the Department of Molecular and Cell Biology, Harvard University, working with esteemed immunologist Professor Jack L Strominger. However, moving from optical benches to pipettes and genes wasn't easy - Davis admits he hadn't got a clue - so he spent six months reading text books 'from back to front, all day and all night'.
Knowledge in hand, Davis was then asked by Strominger to crystallise a protein, a common task for physicists studying biology. He didn't do it.
"I wanted to work on the most important thing in that lab and got involved in basic cell biology projects," he says. "In that first year, myself, Strominger and colleagues published papers in Science and Nature and more. It was such a good, exciting time."
Having already homed in on the action of so-called NK cells, natural killer cells, that can destroy viral-infected or cancerous cells, Davis spotted a gap in the research, where confocal microscopy would prove instrumental.
"Our laboratory and other labs had identified how an immune cell decides whether or not another cell is diseased," he explains. "But why did this recognition take five minutes and what happens with the interactions during this time? It was clear to me that if you could make movies of cells interacting with other cells, you could gain a lot."
Davis's desire to image these cell interactions came just after the discovery of a gene that encoded Green Fluorescent Protein, which could be used to label proteins in living cells, so come 1996 , he turned to state-of-the-art confocal microscopy to image GFP-labelled immune cells.
"I put GFP onto the ends of major histocompatibility (MHC) proteins that were known to be important in how immune cells recognise signs of disease in other cells," he explains. "This was quite a new thing to do and I didn't have any clear hypothesis that I was testing, I just wanted to make movies of the cells interacting thinking I'm bound to see something cool."
And he did. What Davis noticed was that when the NK cell binds with a target cell, its protein molecules move from the surface of the cell to the interface between the two cells. Imaging the contact between the cells, in three dimensions, he then noticed that these proteins actually formed different patterns at the interface, rather than accumulating in a single mass.
"This was really surprising; the fact that proteins moved into structured patterns at the contact of the cells was entirely unexpected," he says. "My instant reaction was, I must have done something wrong so I got my girlfriend to re-do the experiment and check the patterns weren't just some strange artefact from the microscope set-up."
They weren't, and Davis's observations raised the tricky questions; how do proteins make these patterns between cells and what is the importance of this?
An early image of and NK cell checking another cell for signs of disease: Green = MHC protein tagged with GFP; red = intracellular vesicles, including lytic granules. Credit: Davis
Davis's breakthrough also coincided with similar work by Professor Abraham ‘Avi’ Kupfer, then at the National Jewish Medical and Research Center in Denver, and Professor Michael Dustin, New York University. Each was scrutinising the T-cell, a different immune cell, with Kupfer using deconvolution microscopy to image similar activity that Davis had spotted in NK cells.
"Some have said they developed new microscoopy methods to get to these discoveries, but in my opinion, the microscopy needed to see those structured patterns was already there for at least a decade," says Davis. "It was simply the decision to take pictures of the contacts between cells that led to seeing these new things."
But be it microscopy breakthroughs or the decision to image cell contacts, these combined efforts led to the notion that immune cells interact with other cells in a similar way to neurons interacting with each other.
"And this led to common use of the term 'immunological synapse' to describe the contact immune cells made with other cells," explains Davis. "It was an important moment and triggered a lot of interest in the spatial organisation of molecules at immune cell surfaces."
Following the discovery of the immunological synapse, research continued at speed, but Davis was also keen to establish his own laboratory. In 1999, he moved back to the UK to set up his research group in the Department of Biology, Imperial College London, aged only 28.
"The ambition is always to have your own lab and I think its important to do this when you're quite young," he says. "The combination of a good discovery in my postdoc and the UK education system, with its three year degree and three year PhD, allowed me to do this."
Davis spent a year building up his laboratory and applying for research funding, intent on imaging immune cell interactions. He and his team experimented with myriad superresolution imaging technologies , including developing fluorescence lifetime imaging for biological tissue and live cells.
"We've always used state-of-the-art microscopes, but what we have really done is to have this mind-set of, 'well that looks weird, let's study it'," says Davis. "We're always making movies with better resolution; if your microscope is imaging with better spatial resolution than last year, you will start to see new stuff."
Heat mapped 3D-structured illumination microscopy of cortical actin in NK cells; this super-resolution fluorescence imaging technique can give a two-fold improvement in resolution compared to confocal microscopy [Davis, Brown et al. Plos Biology 2011]
During his time at Imperial, Davis also set up a core central imaging facility to diffuse well known tensions between physicists developing microscopes and biologists wanting to use the instruments as presented. As the researcher highlights, this enabled researchers to image live, fixed, unlabelled or fluorescently labelled samples using one of several available microscopes, while physicists develop duplicate versions further.
Davis spent 14 years at Imperial College, and earlier this year, moved up to Manchester University, taking the role of Director of Research at the Manchester Collaborative Centre for Inflammation Research. The move coincided with the release of his popular science book, 'The Compatibility Gene', revealing how our MHC genes determine the behaviour of cells within our immune systems and can impact health, relationships, even individuality.
Meanwhile, Davis and his team continue to pioneer novel imaging methods to study the immunological synapse, having recently used a stimulated emission depletion microscope that provides 3D super-resolution imaging.
Super-resolution microscopy has proved crucial to immunological synapse research, and in a recent breakthrough, the researchers combined photo-activated localization microscopy (PALM) and ground state depletion imaging microscopy (GSDIM) with quantitative cluster analysis to show how individual proteins form nanoscale clusters that re-organise when the immune cell is activated. But much more remains to be done.
As Davis highlights, it is still a challenge to image individual proteins at the contacts between two cells, saying: "When an immune cell sticks to another cell, we know the molecules and proteins that are important but we still don't quite understand all the processes that take place over those few minutes of interaction."
But he is confident this will change. "Using super-resolution microscopy, we will solve this problem over the next decade," he adds. "Still, for me, the big reason to do this, is to watch the cells, and if you see something wacky or unexpected, investigate it."