hello and welcome back to another future
doc house production we are continuing
our journey on hypersensitivity type 4
type 4 hypersensitivity
we've got type 4 hypersensitivity also
known as delayed delayed type
hypersensitivity or DTH you might recall
type 1 was immediate hypersensitivity
whereas type 4 is delayed
hypersensitivity okay this
hypersensitivity is t-cell mediated it's
in red t-cell mediated and it's just
basically about two stories the story of
CD4+ which is a naive t-cell and
CD8+ which is another
naive T cell the CD4 will eventually
become a T helper cell and the CD8 will
eventually become a T cytotoxic cell and
CD means cluster of differentiation all
right let's talk about the story the
story of CD4+ becoming a T
helper cell first a foreign antigen
enters the body obviously second the APC
which is an antigen presenting cell
picks up the antigen hmm and what does
the antigen presenting cell do well it
presents the antigen okay so if we've got
antigen presenting cell we've got a
naive so naive these CD4s
we have a naive CD4+ cell and
they link up the APCs
will present the antigen in
the MHC class 2 molecule and the CD4 has
a CD4 receptor that's the t-cell
receptor the cd4 t-cell receptor and
they're gonna hook up okay and that's
going to lead to some reactions one of
the reactions would be the APCs will
present a protein called b7 and the CD4+ cell will present a protein
called CD28 I know it's all in red know
this memorize this it's annoying
MHC 2 you should know already okay Cd4
well the 4 becomes a TH1 so it's for
help
so that's cd4 the b7 know that's
connected to the APCs and they've seen
you 28 well if there's a CD and there's
a CD4 it's connected to the CDs here we
go
this hooking up this linking of these of
the antigen and the receptor causes the
release of interleukin 12 IL-12 yes more
ILs don't worry
all these interleukins are different
than the interleukins
during the type 1 hypersensitivity so
that should help if you can just
separate these two and list the
interleukins in the different
hypersensitivities you shouldn't be too
confused yes there's an interleukin 12
and it's released and this causes the
CD4 naive CD4+ cells to become a
helper cell a TH1 helper cell simple
now we have a helper cell now we have a
TH1 helper cell I'm sorry effector
cell now it's an effector cell and this
effector cell can release things like
interleukin 2 and IFN gamma these
cytokines interleukin 2 increases the
TH1 proliferation
and the IFN gamma recruits the
macrophages macrophages coming to the
picture as well as helps TH1
proliferation macrophages coming to the
see now now I've got macrophages at the
scene of of this hypersensitivity
reaction and the macrophages release TNF
interleukin 1 and interleukin 6 and
these are all inflammatory cytokines in
these inflammatory cytokines producing
the inflammatory response such as
inflammation while simple fever redness
and swelling so everything that you
think of inflammation that's what the
microphages macrophages are doing by
releasing the TNF interleukin 1 and
interleukin 6 now don't get that confused
because they also release other stuff
which is down here macrophages also
release ROS reactive oxygen species for
you know yeah killing a bacteria is
usually but it's also damaging to the
tissue lysosoomal enzymes and
complement components which all damage
the tissue tissue damage so macrophages
can be very destructive not only are
they used for phagocytosis but they
also release all these fun stuff the
inflammatory factors and the tissue
damage factors all right cytokines well
tissue damage not cytokines but the
cytokines for inflammation and the
chemicals for tissue damage
note that APCs also release
interleukin 6 as well as TGF beta which
is transformation growth factor TGF-beta
which creates TH17 another helper cell
yes but this helper cell releases IL-17
now that simple TH17 releases IL-17 same
number and this recruits the neutrophils
yay so that's where the neutrophils come
into play
so there's macrophages and neutrophils
there's different chemicals that you
know get to this point alright let's
talk about the story of CD8
CD8 is the naive cell ah so naive
the naive cell of CTL cytotoxic t-cells
okay and CT cytotoxic t-cells
I wrote cytotoxic T cell CTLs I don't think
I wrote that wrong CTLs anyway cytotoxic
t-cells okay and the foreign antigen
enters the body the any nucleated cells
any nucleated cells will pick up this
antigen say a virus say you know it
could be anything it's it just virus or
anything it picks it up okay and any
cell which all all nuclear cells has
an MHC class 1 would have the antigen
presented on the MHC class 1 and the CD8
would present it's not present but have
a t-cell receptor of CD8 linking up to
that MHC one okay and class 1 and it
will say oh this antigen is no good we
need to release things and the CD8 would
immediately release perforin and
granzymes the perforin will create pores
in the cell and the granzymes will
cause it to apoptosis so basically the
cytotoxic the killer would just
basically kill the cell and in doing so
probably kill everything else in that
process so that's the CD8 the cytotoxic
T cell all right the disease's the
diseases that type 4 hypersensitivity
causes well this is not really a disease
this is a test for tuberculosis it's
called tuberculin test
it's the tuberculin protein and that's
what's called a PPD a purified protein
derivative and this can cause interferon
gamma and TNF beta to be released by
yours truly the macrophages yes the
macrophages and cause the inflammation
and swelling and
there's this response this inflammatory
response and Boards love to ask you a
question that the patient had a BCG
vaccine which is the Bacille Calmette Guerin vaccine which well come up as a
positive PPD result because of the
inflammation response to the antigen to
the tubular can protein all right let's
talk about other stuff fun stuff here
what we got here we've got contact
dermatitis this is a fun one because
poison oak ivy and sumac they're
everywhere it's they're pretty much
ubiquitous there you you've you will see
a patient with this type of reaction
this type of contact dermatitis and not
only poison oak ivy and sumac can cause
this but also nickel and any other skin
allergies that a patient might develop
because of the hapten carrier mechanism
where a little bit of a molecule from
say something that they happen to be
allergic to gets carried on within their
protein and it becomes a big contact
dermatitis problem all right we've got
CD8 this is an example of a question so
obviously a CD4 and the CD8 can cause a
lot of tissue destruction but say they
asked you a question how does this how
does the cytotoxic cells cause the
destruction in contact dermatitis and
you know see the a cytotoxic t-cells
that's IFN gamma interferon gamma it's
also released so that's that's where
that would come into play also there's
also the perforin and granzymes that
causes the apoptosis of tissue cells so
you can also depend on how the question
is worded answer to the best of your
ability what they're asking for because
a lot of these things can be correct but
they're asking for a specific cytokine
or a specific chemical that's involved
in
in this type 4 hypersensitivity that's
where you can get confused because
everything is very confusing there's IL
12 IL 6 IL 1 there's IFN gamma
TGF-beta just it's insane CD8 CD4 CD
28 well that's a little bit easier
moving on we've got these four which is
all kind of gut related inflammatory
bowel disease celiac disease and Crohn's
disease
look it up they're pretty interesting
gut diseases that are triggered by a
type 4 hypersensitivity I wanted to make
a special mention about this Auto
antibody t-cell mediated response I
don't remember this maybe I didn't pay
attention in school as much as I should
have but apparently this is a this is a
thing where these Auto antibodies are
eliciting a t-cell a t-cell mediated
response and we've got Hashimoto's
thyroiditis which is hypothyroidism due
to type 4 hypersensitivity we've got
rheumatoid arthritis self-explanatory
IDDM insulin dependent diabetes mellitus
type 1 with the destruction of the
B-cells because of the type 4
hypersensitivity Guillain Barre
syndrome which again due to the type 4
hypersensitivity we've got destruction
of the peripheral nerves thus ascending
paralysis all right so that's
hypersensitivity we finished if you
liked this video and you want more of
these videos please click Subscribe
thank you and have a nice day
congratulations you are a medical
student one day you will be a qualified
doctor and your home will be a hospital
or a clinic but for now your journey
begins in the lecture hall you will
listen to countless hours of lectures
and spend evening after evening in the
library reading page after page of
medical theory
and guess what this is the easy part the
hardest part is retaining your medical
knowledge so it's there when you need it
for example examinations but don't worry
we are here to help meet Jeff Jeff is a
good student he goes to all his lectures
he says no to parties so he can stay
late in the library but when it's time
to take the exams
Jeff freezes the knowledge that he spent
so long learning just isn't there
anymore
now meet Jennifer like Jeff she is a
good student but instead of just reading
textbooks late into the night
Jennifer uses technology to help her
study she also watches lectures on
YouTube and practices her knowledge with
QUPI a medical quiz app an online
platform Jennifer likes QUPI because
it has 10,000 practice questions
covering her entire medical course this
means she can practice her medical
knowledge from anywhere and in a way
that actually prepares her for the exams
because she is practicing with exam
style questions when she takes real
exams she'll be ready don't be a Jeff
begin your 7 day free trial with QUPI 
today
