Think about the last time you had a cold.
How exactly did you know
that you were sick?
You had signs and symptoms like congestion,
a sore throat,
maybe a cough or a fever.
And what this told you was that you needed to rest,
drink a lot of fluids,
and maybe reach for that bottle of cough syrup.
But what these symptoms also tell you
is that your immune system is working really, really hard
to try to fight off that infection.
It's trying to get you healthy again.
But have you ever stopped to think about
how these cells that make up your immune system
actually know that you're sick in the first place?
I like to think of the immune system
like a security guard or a police officer
who is patrolling a building.
She's walking through the halls
and looking into various rooms,
trying to assess whether or not the building
is secure or if there's some sort of threat.
Our immune cells do the same type of thing.
They patrol our bodies,
moving through our bloodstream and into our lymph nodes
and other tissues.
And while they're at these sites,
they're looking around to see
whether or not there's some sort of infection they need to fight off.
Today, I'm gonna be talking to you
about a special type of immune cell
called a T cell.
And I think T cells are really interesting,
because the way that they search for infections
is in a very specific manner.
What I mean by this is that
we have lots of T cells in our body,
and some of these T cells
are particularly looking for certain types of infections,
like this cell here may be looking
for the virus that causes the flu,
these cells here may be looking for the bacteria
that cause strep throat, and so on.
So, let's look a little bit more in depth
at this T cell that's looking for the flu.
How exactly does it know if the flu is there?
Well, the cell has this receptor at the surface
that's shown in red.
And what it does with this receptor
is it sort of uses it as its eyes and ears.
The T cell moves around in the lymph nodes and the tissues,
and it kind of grasps around with the receptor
and samples its environment to see what's there.
And if it comes into contact
with a piece of the virus that causes the flu,
you get this sort of nice puzzle piece fit,
a perfect shape match between the bit of flu virus
and the receptor.
And this tells that T cell, there's a threat.
I need to become activated,
and I need to recruit other immune cells to this site
to get rid of this flu infection.
But if you think about it, most of the time,
we don't have the flu; we're perfectly healthy.
But our immune cells are still in this
sort of patrolling function.
They're still sampling their environment,
but what they're coming into contact with
are just totally innocuous pieces of our own cells,
our own tissues.
And so, you don't get that nice puzzle piece fit,
that sort of perfect shape match,
but you do get a little bit of interaction
of this receptor with its environment.
And so, in my research,
I'm really interested in understanding
what kind of information the cells get
from these contacts with normal, harmless things
in the environment,
and how this can go wrong
in the context of disease.
So, you could imagine that if this T cell
sees this harmless little green diamond here
and thinks that it's a threat,
even though it's not,
that cell might become activated
and start to mount an immune response.
But this would be really bad.
It would be as if this T cell is kind of sounding a false alarm
and calling in all the troops,
all the other immune cells,
to fight off an infection that isn't actually there.
And so, this is what happens
in a class of diseases called autoimmune disease,
where the T cells and other cells of our immune system
mediate attack on our bodies
even though there's no harmful or infectious agent present.
And so, there are many different types of autoimmune diseases
that can affect humans,
some of which are shown here.
And it's estimated that between
15 and 24 million people in the US alone
suffer from these and other diseases.
So, it's really important that we try to understand
what kinds of things can go wrong
with T cells and other immune cells
that can lead to this kind of disease.
And so, I've been particularly interested in lupus.
Now, lupus is a really complicated disease.
Some patients present with this sort of classic
malar butterfly-shaped rash on their face.
But not all -- it's only about 30 to maybe 60% of people.
Other patients have problems with their kidneys,
their brains, the levels of iron in their blood.
So, because lupus is such a complicated disease
and there are so many different manifestations of it
that can occur in patients,
this implies that there are probably
many different types of things that can go wrong.
So, it's important to study a lot of different types of models of lupus
to figure out all of the many different types of things
that can go wrong.
And so, for my research,
I was interested in using one of these models of lupus
to try to figure out
what is actually causing these T cells
to sound the false alarm.
Why are they starting to attack our own normal, healthy bodies?
So, it's very hard to do this kind of research on people.
So, instead, I turned to a mouse model.
Now, mice don't get that classic malar rash,
and even if they did it would probably
be pretty hard to see with all that fur.
But what we can do instead
is perform a simple blood test
to see if the mouse has a disease that looks like human lupus.
And so, in this mouse that I started studying,
we looked at its blood
and found that there were antibodies present
that can cause harm to our own tissues.
So, that meant that this mouse had lupus,
or a disease that looked like lupus.
And then, when I looked at the T cells in these mice,
they actually looked activated.
They looked like they were responding
to some sort of infection,
but the mouse was not sick at all.
It didn't have any virus or bacteria around.
And so, to try to figure out
what was going on in the T cells of this mouse
that was causing disease,
I looked at the mouse's DNA
and wanted to know whether there were any genetic changes,
any mutations,
that could be contributing to the disease.
And so, by sequencing the DNA,
I found that there was a single base pair change
in this gene called Rasgrp1.
And so, I wanted to start investigating
how altering this molecule, Rasgrp1,
could lead to these disease features
that we see in the mouse.
So, what does Rasgrp1 actually do?
Well, the gene encodes a protein
that's really important for turning signaling pathways
on inside of cells.
So, if we have our T cell here,
and let's say it's that flu specific T cell from before...
if this T cell sees a bit of the flu,
it knows it needs to become activated.
So, what is going on with Rasgrp1?
Well, Rasgrp1 activates a couple of
downstream signaling pathways,
one of which is called Ras,
and the other is called mTOR.
And for reasons that I'll explain to you later,
I became very interested in this mTOR pathway.
Now, mTOR is a kinase,
so it phosphorylates downstream proteins to turn on signaling.
And mTOR signaling is very important
for a number of different processes in T cells,
including their activation.
But let's take a step back.
This example here is showing you
what happens when that flu-specific T cell
sees and interacts with the flu virus
and becomes activated that way.
But most of the time, as you know, thankfully,
we don't have the flu.
We're not always sick.
And so, I was really interested in whether this signaling pathway
from Rasgrp1 to mTOR
was also present in cells
from just a normal and healthy mouse.
And so, to address this,
I took T cells out of normal and healthy mice,
and I measured the level of signaling
through Rasgrp1 to these pathways,
Ras and mTOR.
And what I found was that Rasgrp1
does send a low level of signal to mTOR
in these normal, healthy T cells,
but not to Ras.
So, it seemed like this mTOR pathway
was really important in the normal and healthy cells.
And what this also told me is that
T cells can experience a range of mTOR activity.
So, in the context of infection,
they get a really strong signal.
And in a normal and healthy T cell,
they get a lower level of signal,
but it's not zero -- there is still a little bit of signal.
And I think this is particularly important
for T cells to perform this sort of
police officer/security guard function.
It helps them patrol and stay alert
so that they're ready to respond and activate
really quickly when that infection does come.
So, once I established that Rasgrp1
seems to send this low-level signal
to the mTOR pathway in normal cells,
I wanted to know what was happening in the T cells
from that mouse that had lupus,
because I knew that those T cells
had a mutation in this gene, Rasgrp1.
And so, what I found when I measured
the level of mTOR signaling in these lupus T cells
was that it was actually a little bit increased
relative to a normal or healthy cell.
And so, this cell was sort of somewhere
in between the normal context and the infected.
And so, this made me really wonder
whether having this little bit of increase
in mTOR activity in the Lupus T cells
was what was actually causing the disease.
So, to address this question,
I took advantage of the fact
that there's a drug that can block, or inhibit,
the activity of mTOR.
And this drug is called rapamycin.
And actually, the word mTOR itself
stands for mechanistic or mammalian target of rapamycin.
And so, what I did is I took this drug
and I administered it to the mice
that had lupus (and this Rasgrp1 mutation)
as well as to normal, healthy, wild-type mice.
And then I measured
the level of the T cell activation
that I observed in these animals
as sort of a readout of whether they had disease or not.
So, if I just looked at the mutant mice,
without giving them any drug,
as I told you before,
there was this high level of T cell activation.
The mice kind of looked like they were responding to an infection,
even though one wasn't there.
But if I treated the mice with this drug
to turn down the mTOR signaling,
I saw a reduction in the amount of activated T cells in this mouse,
to about the levels of what you see
in a healthy, normal animal.
And so, this really showed that the lupus-like disease
in these Rasgrp1 mutant mice
was caused by that increase in mTOR signaling
that I observed.
Now, another feature of autoimmune disease
can be the accumulation of sort of specialized T cells.
And what do I mean by this?
If we think back to that security guard,
she's kind of generally walking around the building,
looking to see what's wrong.
But if she saw that there was a fire,
she would want to specifically bring in the fire department,
and not just the police force.
And so, you can think of these specialized T cells
as those firemen that would come in.
And so, if you look in a normal and healthy mouse,
you have a few of these specialized T cells.
But when I looked in the mouse with the Rasgrp1 mutation,
I found that there were actually
a lot of these specialized T cells,
which is depicted in this graph here.
And if I administered that drug, rapamycin,
to turn down the mTOR signaling,
I found that this population of specialized T cells decreased.
So, it showed, again, that these specialized T cells
were accumulating in a manner that was dependent
on having some mTOR signaling in the cells.
And so, now I've shown you
that there is this signaling pathway
from Rasgrp1 to mTOR
that seems to be increased
when you get this single nucleotide change in Rasgrp1.
And this leads to a lupus-like disease in the mice.
Now, I told you that mTOR signaling controls T cell activation
and that I saw that the T cells
in these Rasgrp1 mutant mice
looked like they were activated.
And I also saw an accumulation
of these specialized T cells
that may be due to increased proliferation,
which is also a process driven by mTOR.
But I wanted to know from here,
what might be going on inside the cell,
at the molecular level,
that could be causing the T cells to become activated?
So, not just the signaling,
but what was sort of connecting the signaling to the activation.
And so, from here, I started to look
at this process of translation
-- so, going from mRNA into protein --
because this is a process that's known to be
very tightly controlled and regulated
by mTOR signaling.
So, again, translation
is this process of going from mRNA into protein.
And to see whether translation
might be altered in my Rasgrp1 mutant mice,
I started by looking at one single gene, called Gata3,
as a proof of concept.
Now, Gata3 is known to be very important
for the regulation and development
of these specialized kind of firefighter T cells,
and so that's why I chose to look at it first.
So, to see if Gata3 was regulated
at the level of translation,
I looked at its levels of mRNA
in just a normal, healthy, wild type mouse
compared to the Rasgrp1 mutant.
And I didn't really see any changes.
So, it looked like they had about the same level of mRNA.
But when I measured the protein levels of Gata3,
I found that the mutant T cells
had about twice as much protein,
so it seemed like there was something happening
between this step of mRNA to protein
to cause that to accumulate,
and so I thought this might be due
to an increase in translation in the mutant T cells.
Now, this data was really exciting,
and it made me want to look at more and more genes.
But instead of just picking ones that made sense to me,
I wanted to take a more unbiased approach
and instead look at all of the genes
in the genome.
And so, to do this,
I used a really cool new technology.
The first step was to just isolate
all of the mRNA from T cells,
to get a representation of which genes
were expressed and at what levels.
And this is called RNA sequencing.
But to look specifically at the mRNAs
that are being translated,
what I did was a technique called ribosome profiling.
So, I took the ribosomes out of cells
and isolated the mRNAs
that are bound to those ribosomes
-- so, only those mRNAs that are actively
being translated in the cells --
and then I sequenced that RNA as well.
And by comparing the level of expression
in the ribosome data set to the mRNA,
I could get a sense of which genes
were being regulated at the level of translation.
And I was really excited to see
that there were around 600 genes
that seemed to have increased translation
in the mutant T cells compared
to the normal, wild type ones.
And this is a really ongoing, active area of research
in my lab now,
to try to figure out what these genes are doing in the T cells
and how they may be contributing to the disease.
And so, this is an exciting, open question
that we're hoping to answer later on.
So, by studying this Rasgrp1 mutant mouse,
I was able to learn a lot of different things
about T cell biology
and how it relates to disease.
I showed you that T cells
have this sort of range of mTOR activity,
and that normal, healthy T cells
have a little bit of mTOR signaling
that helps them perform this patrolling function --
it helps them stay alert and ready to respond.
But if you have a mutation in this gene, Rasgrp1,
and it increases the level of mTOR signaling a little bit,
this can cause that T cell to increase its mTOR activity
and then that T cell can become more activated,
can start to become more specialized,
and can... star...
can contribute to the lupus-like disease that we see in the mice.
And we think that this is due to mTOR's regulation
of translation in cells.
And so, this is what's sort of causing
the T cells in this model
to sound that false alarm.
They have this little bit of elevated mTOR activity
and they're... instead of knowing that everything is fine,
they are contributing to disease.
And so, this research, I think,
leads to a lot of really interesting questions
and future directions.
So, is this phenomenon of increasing the level of mTOR activity
in a T cell
only applicable to this model of lupus,
or is it true for other types of autoimmune diseases as well?
Is this sort of a universal,
or a unique, phenomenon?
Additionally, I looked at the mTOR pathway
in these T cells from these lupus mice
and saw differences,
but perhaps other signaling pathways are also altered
in normal T cells in the context of autoimmune disease.
And perhaps these other pathways
also sort of tune the reactivity of those cells.
And in general, I think this research
shows that performing basic research
to understand signaling pathways
and general T cell biology
is a way to get a deeper understanding
of autoimmune diseases like lupus,
and hopefully one day will contribute
to our ability to design
better, more rational therapies to help patients.