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- [Narrator] We are the paradoxical ape.
Bipedal, naked, large brain.
Long the master of fire,
tools and language,
but still trying to understand ourselves.
Aware that death is inevitable,
yet filled with optimism.
We grow up slowly.
We hand down knowledge.
We empathize and deceive.
We shape the future from
our shared understanding
of the past.
CARTA brings together experts
from diverse disciplines
to exchange insights on who
we are and how we got here.
An exploration made possible
by the generosity of humans like you.
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- Hello, thank you to the CARTA organizers
for inviting me to do this talk
and share with you some
of the exciting work
we've been doing over the years
on the interaction
between infectious agents
and our own human body system.
So the title of my talk
"are their distinctly
human infectious diseases?"
But since I'm a pathologist,
I'm going to show you a lot about
some of the pathology that goes on
after the infectious
diseases have infected us.
So, this is the list of different topics
that we had discussed over the years
as candidates for
distinctly human diseases.
There are a whole lot
of definite candidates
like myocardial infarction and carcinomas,
cancers of epithelial origin.
But as you can see, most
of the items on this list
are infectious diseases.
And so today, I was and this
next slide shows you in red,
many, all of the infectious
diseases that were on that list.
So, as you can see from this
next image, data compiled
from the Centers for Disease
Control and Prevention,
and published in the New
England Journal of Medicine.
In 1900, most of the deaths
occurred due to infect diseases,
as you can see
gastrointestinal infections,
tuberculosis, pneumonia, influenza.
Now in 2010, most of the deaths in humans
occurred because of
cancer or heart disease.
Heart disease is the primary cause
and infectious diseases has fallen
to a very small percentage.
Now the reason for that, of course,
is probably due to the use of vaccines.
And most of the first vaccine
that helped eradicate a
disease was small pox.
And now we're working on polio.
A lot of the different vaccine
to these different diseases
have been discovered, and
are being used effectively.
And as the causes of death
in chimpanzees though
are a little different,
as you can see here,
a whole list that is hard for you to see,
but in an autopsy review
of about 35 years of data,
they showed that it's cardiac events
that causes the highest
mortality in chimpanzees.
But these cardiac events
have a different pathology.
It's not coronary thrombosis
that happens in humans,
it's interstitial fibrosis in chimpanzees.
So now diving into some of the diseases
that may be distinctly human.
I'll start off with talking
about human influenza
and then give you a little
background on some of our work
on typhoid, cholera and then gonorrhea.
So, as an introduction, as I
wanted to talk to you about
the cell surfaces,
as you are concentrated on DNA making RNA,
going on to make protein,
but the cell is not really done
until it makes the surface carbohydrates
which are called glycans,
glycoprotein glycolipids,
and at the very tip of these glycans
are these diamond-shaped structures
that are known as sialic acids.
The sialic acids are the terminal,
very end monosaccharides
attached to the underlying
cell surface glycoconjugates
and have been shown to
show many important roles
in the microbe binding
that leads infection,
that will be the topic of the talk today.
Regulation in immune response,
progression and spread
of human malignancies,
and in certain aspects of human evolution.
Now the sialic acids can be attached
to the underlying glycans
in different linkages.
These linkages as depicted here
may be alpha two, three, six linked,
alpha two three linked
to the underlying glycan,
alpha two, six linked to
the underlying glycan,
or alpha two, eight linked
to the underlying glycan.
Now, why am I showing this?
It's because we've shown
it on several studies
that most pathogens like to bind
to the alpha two, three linked
sialic acids as shown here.
But human influenza
virus is unique in that,
it likes to bind to the alpha
two, six linked sialic acids.
In some studies we did
couple of decades ago,
with Pascal Gagneux,
here are some sections
of the human trachea,
sections of the chimp,
and gorilla and mouse
tracheal epithelium, and
the blue is the binding
of the SNA light lectin
which specifically binds
to alpha two, six linked sialic
acids and you can see here,
it's very on the outer edge
of the epithelial cells
as the lumen of the trachea,
it's not present on the
epithelial cell edges
in the chimp or the gorilla or the mouse.
There's some present in the mucin
but this is what the flu virus sees,
as it's passing through,
and likes to bind to
on the very edge, the alpha
two, six linked sialic acids.
Further studies done by Miriam
Cohen in Dr. Gagneux' lab,
where she used the three different
influenza viruses depicted here.
Influenza viruses, you've
heard them called H1N1 or H3N2.
So H refers to the hemagglutinin
and that is what allows
the virus to adhere,
agglutinate and then uses
the N or the neuraminidase
as like scissors to clip through the mucus
and then allows the virus to enter further
and attach to the
epithelial cells under here.
This the negative control
showing no attachment.
So her studies showed that
the human influenza viruses,
actually uses neuraminidase to,
after the attachment to attach
to the underlying structure.
The Tamiflu, the mechanism
of action of Tamiflu
is to inactivate this neuraminidase.
So even though the virus may attach,
it cannot go further and infect
the underlying epithelial cells.
So, that was the virus in affecting
our human tracheal mucosa.
Now I'll go on to talk about
the sialic acid further.
There are two major kinds of sialic acids
on mammalian cell surfaces.
There's a Neu5Ac and the Neu5Gc,
and the only difference between
the two is one oxygen atom.
The Neu5Gc is shown to
be missing in humans,
because there is the CMAH gene,
which converts Neu5Ac to Neu5Gc.
The CMAH gene were shown to
be inactivated in humans,
about two to three million years ago.
So humans make Ac and not Neu5Gc.
So we were able to make a mouse model
which lacked the CMAH gene
in studies of human disease.
This is called the Cmah Null mouse.
These animals have been
studied for many years,
and have been observed
to demonstrate a lot of
human-like diseases like atherosclerosis,
carcinomas as depicted here,
age-related hearing loss,
delayed wound healing,
increased inflammation
and immune response,
altered susceptibility
to muscular dystrophy
and interestingly, the Cmah Null mice
show the ability to run
longer than controls.
That's why human can runs marathons,
whereas chimpanzees don't really,
they basically jump up and down.
So we use this cmah Null mouse in a lot,
studying a lot of these human diseases.
So the first one is going
to talk about was cholera.
Vibrio cholerae was first
isolated by Filippo Pacini
and his discovery was not
widely known until Robert Koch,
who worked on tuberculosis
and described the mechanisms
about 3030 years later.
And Koch had these postulates saying that
the microorganism must
be found in abundant
in all organisms suffering
from the disease.
Microorganism must be isolated
from the disease organism
grown in pure culture.
The cultured microorganism
should cause disease
when introduced into healthy organism.
And the microorganism must be re-isolated
from the inoculated
disease experimental host
and identified as being identical
to the original specific causative agent.
So those were his passwords.
But when he started studying cholera,
in 1884, he wrote in the
British Medical Journal
saying that all these,
although these experiments
were constantly repeated with material
from fresh cholera cases,
our mice remain healthy.
Then made experiments on
monkeys, cats, poultry,
dogs and various other mammals.
But were never able to
arrive at anything in animal
similar to the cholera process.
So, Vibrio cholerae does
not naturally cause diarrhea
in adult mammals other than humans
or in gene altered models.
Now, cholera is a noninvasive pathogen,
symptomatology occurs due to
production of an exotoxin,
encoded by a virulent factor.
The toxin has an A subunit
and five B subunit.
And we shown that these, the B subunit
is what binds to the ganglioside receptor
on the intestinal epithelial cells.
And then through several steps,
intracellular cyclic
adenosine monophosphate
opens the cystic fibrosis
transmembrane regulator
and chloride ions are
released into the lumen.
And so, this causes the epithelial cells
of the small intestine to
secrete fluids and electrolytes
and cause the watery diarrhea
that can only be treated by
extensive IV fluid replacement.
So here's a diagram showing
the cholera bacterium,
invading through the mucus
and then using neuraminidases
to expose the ganglioside receptor
on the surface of epithelial
cells to which it then binds.
So the, so here is a complex
mixture of gangliosides
all containing sialic acids.
But it's been shown
that the Vibrio cholerae
uses these neuraminidases to finally
expose the GM1 ganglioside
to which it then binds.
So the GM1 ganglioside is a component
of the cell plasma membrane,
which modulates cell
signal transduction events.
So, we use the Cmah Null mice
to study the cholera process.
And here are intestinal
loops that were infected
with cholera, from the wild type
and from the Cmah Null mice,
showing distended ileal loops
filled with watery fluid
in the Cmah Null mice
but not in the wild type.
Then when we use sections
from these same animals
and saw that there isn't much binding seen
with the cholera toxin by itself,
but then when we use the neuraminidase,
you can see lots of binding
to the Cmah Null mice
epithelial cells in
different concentrations,
but which is not present
in the wild type mice.
So this again demonstrates that it binds
to the underlying ganglioside receptor.
So next candidate that
is going to talk about
is typhoid fever.
It's caused by Salmonella
enterica serovar Typhi,
results in 200,000
annual deaths worldwide.
There's the toxic subunit,
and then the beta subunit,
which is the binding part,
which specifically recognizes glycans
present in the human-enriched
sialic acid Neu5Ac.
So here is a diagram of the
GI tract in the human adult,
which if you go down into that tube
and take sections and look
at it under the microscope,
you can see these
fimbriae finger-like villi
which allow a lot of the absorption
to occur in the small intestine,
and under the epithelium are
these lymphoid Peyer's patches.
The surface epithelium that lies
above these lymphoid Peyer's
patches are called M cells.
And those are the cells with
which the typhoid bacillus
interacts with before it starts invading.
So here again is a picture
of the normal small intestine
and a blown up view of that
and a diseased small intestine
full of inflammatory cells and edema.
So, and we've shown that
the typhoid toxin binding
is human-specific, as you can see here,
it recognizes Neu5Ac enriched sialic acids
and not Neu5Gc sialic acids.
And then frozen sections of
small intestines from humans,
or chimpanzees using fluorescently
labeled typhoid toxin,
or its binding defective PltB
mutant as a negative control,
shows binding on the human sections
and no binding to chimpanzee
sections of small intestine.
Last thing to remember
about typhoid toxin,
that an asymptomatic carrier
state of some diseases
was described first in typhoid.
So Karl Joseph Eberth first
described the bacillus
that caused typhoid in 1880.
And four years later, a pathologists,
as we pathologists continue to do,
demonstrating the actual
process of the disease
that actually happened, confirm this link
named bacillus typhi,
which is now known today
as Salmonella enterica.
So an asymptomatic carrier state
was first described by
this person Mary Mallon,
who was then known as Typhoid Mary.
She was an Irish born cook,
believed to have infected 51 people
with typhoid fever and
the first person in the US
identified as asymptomatic
carrier of the disease.
Because she persisted working as a cook
by which she exposed
others to the disease,
she was twice forcibly isolated
by authorities and died
after a total of nearly
three decades in isolation.
So what was not known then was that,
the bacillus actually
resides in the gallbladder,
hides out and one treatment
for the asymptomatic carrier
would have been to remove the gallbladder
but that was not known at that time.
Now of course, that is a treatment
to avoid the asymptomatic
carrier state of typhoid.
The next thing is gonna
talk about was gonorrhea.
Neisseria gonorrhea causes
the sexually transmitted
disease gonorrhea.
WHO estimates about 106
million cases per year.
About a one third of these
are multidrug resistant,
there is a high frequency
of asymptomatic infections
occurring in women.
Untreated gonorrhea can lead
to pelvic inflammatory disease
and infertility.
Gonorrhea has not been
observed in other species,
the disease model in
chimpanzee was not successful.
The molecular evidence is
that the human factor H
binds directly to one of the proteins
on the surface of the gonococcus
and leads to serum
resistance only in humans.
So here are some pathology
pictures of a uterus.
This is the uterus, the
fallopian tube and the ovaries.
This is uterus and fallopian tubes
that are removed from a patient that had
pelvic inflammatory disease
with fallopian tubes
that were absolutely
swollen and full of pus.
If the uterus are allowed to remain,
this would heal and cause scarring
and lead to infertility.
This is a picture of a uterus
that was removed and opened up.
This is the cervix in the outside,
this is the endocervix
and the endometrium.
If you looked at sections of
this under the microscope,
this part outside of the
cervix and the vagina contained
is made up of squamous epithelium,
whereas the inner inside
is columnar epithelium
as is shown here.
The gonococcal bacteria like to bind
to the columnar epithelium shown here.
And as shown in this
slide, the gonococcus,
the components is made up of pili,
and several different proteins
and a lipopolysaccharide.
This is a scanning electron micrograph
of fallopian tube explants showing
non-ciliated and ciliated cells
and showing that the
gonococcus actually binds
to the non-ciliated and
not the ciliated cells.
And this a picture
pulled from the internet,
reminded to tell you that the gonococcus
acts like a wolf in sheep's clothing.
Because what it does is, here's a diagram
showing the diplococcus in gonorrhea
with the cell surface proteins.
It acquires sialic acids from the host
using enzymes from the host.
And this sialic acid then interacts
with the cell surface
receptors which are Siglec,
which are sialic acid
recognizing lectin-like receptors
on the surfaces of the
columnar epithelial cells
of the endocervix.
So that's how the binding occurs
and then further infection.
So these are photographs of
images from human cervix,
showing expression of these receptors
on the columnar epithelium of the cervix.
And when we looked at chimp epithelium,
it can be show here
that the human Siglecs,
which are shown in black,
bind better to the Siglecs
than the chimp Siglecs.
So, that brings me to the end of my talk
with this list that I showed you earlier,
which are candidates for
distinctly human diseases.
And today I spent time talking
about four of these diseases.
So infectious diseases are
caused by a variety of pathogens.
The human body is made up
of about 10 to 13 cells
and hosts about 10 to 14 other microbes
which are bacterial, fungal, protozoal
and non-pathogenic viruses.
All of which are part of the normal flora.
Pathogenic organisms are
distinct from normal flora
and have developed highly
specialized mechanisms
to invade and elicit specific responses,
which contribute to survival.
Bacteria classified into
spheres, rods and spiral cells.
And virulence genes confer
the ability to infect
and may be carried by
bacteriophages or bacterial viruses
as in Vibrio cholerae
organism which cause cholera.
So that brings me to the end of this talk
and thank you for your attention.
I hope I've communicated
some of my excitement
in discovering some of
the pathology behind
some of the events that
occurred in infectious diseases.
And perhaps I may have inspired
some of the medical students out there
who's been listening to this,
to consider pathology as a career,
'cause you can not only
do research and clinical
and be a physician's
physician in your future.
Thank you, bye.
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