Cell-Mediated Immunity (Lecture 5)

Question 1

Cell-Mediated Immunity

-Recognition of Antigen by T Cells

Answer 1

YA

Question 2

Recognition Of Antigen By T Cells

B cells utilize ____ as their cell surface antigen receptor and can therefore recognize soluble antigens as they exist in their native conformation.

Do T cells utilize a molecule similar in structure and function to antibodies as an antigen receptor?

Answer 2

antibody

Question 3

Recognition Of Antigen By T Cells
A major mechanism through which viral infections are eliminated is via ____-mediated killing of infected cells.

Cells infected with replicating viruses express virally-encoded proteins in their native conformation on the outer aspect of their ____.

How do cytotoxic T cells recognize virally infected cells and subsequently kill them?

Answer 3

T cell

plasma cell membranes

Question 4

Recognition of Antigen by T Cells

Zinkernagel and Doherty: How do the CTLs specifically recognize LCMV-infected target cells?

Hypothesis: CTLs have receptors that interact directly with intact ____ proteins on the surface of infected target cells; engagement of the receptor leads to killing of the target cell.

Answer 4

viral

Question 5

Zinkernagel and Doherty Experiment

Chromium Release Assay

take target cells and incubate them in media that has radioactive ____ in it (the isotpe = 51); the cells will passively take up Cr51 intracellularly and keep it within the cytoplasm

then, take the radioactively labelled target cells and mix them with a hypothetical population of killer cells; prior to interaction of activity bt target and killer cells > everythings been sequestered by target; all of the radioactivity is associated with the ____ cells

incubate target cells for 6 hours, killer kills some of targets, the Cr51 is released into the ____ (run through a scintillation counter) > you start to radioactivity in the media

amount of radiation found within the media is directly related to the number of ____ that have been killed by killer T cells

strain A mouse, inject it with LCM virus > induce a response (bc adaptive immune response)

week later, boost the animal again, then isolate the T cells (cells from spleen, lymph nodes, or both) > utilize the assay (incubate with killer cells and cells of different type (uninfected and infected))

Answer 5

chromium
target
media
target cells

Question 6

Zinkernagel and Doherty Experiment

no killing, bc the response that we’re inducing has ____ to it (must be LCMV specific, with the proteins)

proteins expressed on the strain B is the same as the proteins expressed on the strain A

if proteins are expressed, but on a different cell type > no ____

Answer 6

specificity

killing

Question 7

Conclusions:
- CTLs must recognize ____ molecules and ____ MHC molecules of the
infected strain on the surface of a target cell in order to kill it.
- MHC molecules do not function solely as alloantigens that mediate graft rejection but more importantly have a role in recognition of ____.

Concept of MHC Restricted Recognition of Conventional Antigens by T Cells

CD8+ cytotoxic T cells recognize peptides bound to self ____ MHC molecules.
CD4+ helper T cells recognize peptides bound to self ____ molecules.

Answer 7

viral
conventional (microbial) antigens

class I
class II

Question 8

How can MHC restriction be explained in the context of an antigen receptor?

Dual Recognition Hypothesis:
- CTLs have two distinct antibody-like receptors on their cell surfaces that must be
engaged ____ in order for the target cell to be killed; one for ____ antigen and the other for a ____ molecule.

Altered Self Hypothesis:
- CTLs have a single antigen receptor that recognizes a ____ molecule modified
by viral molecules.

Answer 8

simultaneously
viral
self-MHC

self-MHC

Question 9

The T Cell Antigen Receptor

So this the ____ form of the antigen receptor. They are two ____ pretty much the same size. They both have ____ and ____ domains. They both have variable and constant regions. The variable regions make up the amino terminal half of the alpha beta chains, and the constant regions make up the carboxy terminal halves of the alpha and beta proteins. So in some ways what does this look like? Answer: Almost half of an ____ molecule. Yet it doesn’t behave or function in a manner that closely resembles the way antibody molecules do.

Answer 9

alpha beta
glycoproteins
transmembrane
cytoplasmic
antibody

Question 10

The T Cell Antigen Receptor

The other series of proteins that I want to point out to you at this point are over here (on right), and it is actually a family of proteins that aggregate with one another to form a molecule or structure that is referred to as ____. Remember I told you that this is the ____ cell marker. CD3 is composed of epsilon chains, delta chains, gamma chains, and what are referred to as ____ chains. And the function of CD3 is to act as a mechanism for ____ signal transduction once the antigen receptor has engaged whatever it is it’s specific for. So CD3 has nothing to do with dictating the ____ of the T cell. It functions as a mediator of ____.

Answer 10

CD3
pan T
zeta
amplifying
specificity
signal transduction

Question 11

The T Cell Antigen Receptor

So how does this thing work? What they recognize are peptides derived from those proteins in association with self MHC molecules. The self MHC associates with the ____ derived from, for example, a viral protein.

They recognize peptides derived from those proteins associated with ____ molecules on the surface of the target cells.

Answer 11

peptide
self class I

Question 12

Comparison of the B and T Cell Antigen Receptors

But again, it will not recognize proteins in their native conformation, which antibodies are fully capable of doing. T cells require that the protein be denatured ____, resulting in the generation of peptides that are then expressed on the surface of the target cell in association with self class I molecules. And that is something that the T cell antigen receptor can bind to. So at this point, I’m not really interested in you understanding how the peptides are generated and how they get on the cell surface. But just the concept that the antigen receptor has to interact with a peptide and a self class I if it’s a ____, T cell or self class II molecule if it’s a ____ T cell.

Answer 12

intracellularly
CD4+
CD8+

Question 13

Recognition of Antigen by T Cells

interacts with the complex formed by the ____ peptide and the ____ molecule > serves as activation (engagement of antigen receptors, and secondary signals derived from other cells)

upon binding, initiates apoptosis on target cell and ultimately kill it

the strain A nucleated CTL (killer) cell also have ____ molecules, even the killer cell can be targeted and destroyed

Answer 13

viral
self class I
self class I

Question 14

Zinkernagel and Doherty Experiment

no infection, peptides are derived from ____ proteins (shows self, uninfected); t-cells do not recgonize these peptides

and then in the last scenario, there is a cytotoxic T cell coming from a virally infected animal, now mixed with a strain B LCMV infected target cell. They’re over here, but the fact that it’s not the appropriate ____ molecule, the T cell can’t recognize this complex and leaves it alone.

Answer 14

cellular
class I (allogeneic MHC)

Question 15

Recognition Of Antigen By T Cells

1. T cells are specific for ____ sequences of discrete peptides; not intact soluble proteins.
2. T cells only react against foreign peptides when they are attached to the ____ of another cell (antigen presenting cell).
3. T cells from any one individual will only recognize foreign peptides when they are complexed with the ____ molecules of that individual.

Answer 15

amino acid
surface
class I/II

Question 16

Recognition of Antigen By T Cells

So how do these complexes form? So we have to go back and appreciate the structure of class I and class II molecules. We talked about the fact that they have binding clefts and now you know that what fits into these binding clefts are ____. Different class I molecules will bind different sets of ____. Different class II molecules will bind different sets of ____.

Answer 16

peptides
peptides
peptides

Question 17

Recognition of Antigen by T Cells

And you as an individual have the class I molecules you inherited from your ____ and your ____. So that gives you, I’d have to do the math, but that probably gives you ____ different types of class I molecules.

And then you have the genes encoding class II molecules that you inherited from your mother and your father. And there’s thought that the alpha and beta chains from the mother and father can actually associated with one another so that there can be ____ class II molecules produced. So that gives you, again I’d have to do the math, on the order of ____ class II molecules on the surfaces of your cells.

So it’s not a huge number, but it’s sufficiently large enough that you can take peptides from a ____ number of microbes and show them to T cells.

Answer 17

mother
father
10 or 15

“hybrid”
20 or 30

huge

Question 18

Antigen Presenting Cells

The responses of antigen-specific T cells require the participation of accessory cells that “capture” the antigen, process it into ____ fragments that are then displayed on the cell surface in association with a ____ molecule. Collectively, the cells that perform this function are know as ____.

____ are the only antigens that can be processed and presented to T cells!

Things have changed a little bit, so that the term antigen presenting cell, in a very generic sense, can be either a ____ or a cell that processes and presents an antigen in a context of ____ molecules.

Answer 18

peptide
MHC
antigen presenting cells

proteins

target cell
class II

Question 19

Antigen Presenting Cells

All ____ cells express class I MHC molecules and therefore can process and present antigens to ____ cytotoxic T cells.

Only the limited number of cell types that express class II MHC molecules can also act as ____ for CD4+ helper T cells. These unique cells are referred to as ____ antigen presenting cells.

Answer 19

nucleated
CD8+

antigen presenting cells
“professional”

Question 20

Professional Antigen Presenting Cells

Main Functions

____ – presentation of antigen to naïve T cells and initiation of responses to protein antigens.

____ – effector phases of cell-mediated immune responses.

____ – presentation of antigen to CD4 T cells in humoral immune responses.

Answer 20

dendritic cells
macrophages
B cells

Question 21

Antigen Processing and Presentation

Cytosolic proteins are typically synthesized within the cell and include:
- \_\_\_\_proteins
- \_\_\_\_ proteins
- intracellular bacterial, fungal and
parasitic proteins
- mutated \_\_\_\_ (tumors)

Occasionally, peptides derived from microbes and other exogenous antigens can enter this pathway by passing from a ____ into the cytosol.

Class I, or Class II pathway

Class II: the protein that is processed and presented comes form outside the cell (macropinocytosis, pinocytosis, RM endo, or phago); the antigen is ____ to the cell itself

Class I (self): biosynthesized ____ the cell itself, the proteins are endogenously derived (our own, proteins encoded by viruses, intracellular bacteria, and protozoa)

Answer 21

self
viral
self proteins
phagosome

exogenous
within

Question 22

T Cell Activation

Similar to B cells, activation of T cells requires ____ signals.

These come in the form of:
• a primary signal derived from the binding of the ____ by the T cell receptor
• secondary signals that are provided by ____ molecules expressed on the the surface of the antigen presenting cell as well as ____.

So on the surface of the antigen presenting cell is a self class II molecule with a peptide associated with it, a configuration that the T cell antigen receptor can interact with. The other molecule that you’ll see is the CD4 molecule. I’m going to say this and I hope it doesn’t confuse you: the CD4 and CD8 molecules bind to non polymorphic components of either class II or class I molecules. So CD4 binds to a portion of class II molecules that is ____ in all of us. CD8 binds to a non polymorphic component of class I molecules that is ____ in all of us.

The secondary signals, which in this diagram are represented by the green arrow, are ____ signals that are derived from the interaction between receptors and ligands on the surfaces of the antigen presenting cell and the T cell, as well as from ____ that are released by the ____ and binding to specific receptors on the T cell. Analogous to what we saw with B cells.

Answer 22

peptide:MHC complex
co-stimulatory
cytokines

identical
identical

co-stimulatory
cytokines
antigen presenting cell

Question 23

T Cell Activation

And then when all of that happens, we end up with this signal transduction cascade that ultimately leads to the activation or expression of ____, which find their way into the nucleus and then induce the expression of genes encoding proteins that are required for initially the ____ of of the T cell, and then secondarily the ____ of the T cell.

Answer 23

transcription
proliferation
function

Question 24

T Cell Activation

REWATCH

helper t cells produce ____ themselves; they also express the genes for the ____; ____ form of growth regulation

Answer 24

IL-2
IL-2R
autocrine

Question 25

Cell-Mediated Immunity

• Effector Mechanisms of Cellular Immunity

Answer 25

YA

Question 26

Cytotoxic T Cells

This represents one of at least ____ pathways through which effector CTLs can be generated.

If a professional APC is directly ____ or it has phagocytosed an infected cell it may be able to activate a CTL precursor independent of ____ T cells.

in this scenario, its including presence of CD4 positive helper T cell

• so this is just 1 scenario where cytotoxic T cell could be activated
• so helper cell is providing some of secondary signal that is required for activation of this cell -in this case, secondary signal is ____, which is binding to the IL2 receptor on the cytotoxic T cell

Answer 26

three
infected
CD4+

Question 27

Cytotoxic T Cells

The original activation we discussed

start w/ mechanism that cytotoxic T cells recognizes a target cell and ultimately kills it -recognize that activation of T cell is a ____ step process
1. step 1: engagement of ____ receptor
2. step 2: secondary signal being provided via interaction of receptor and ligands expressed on surface of ____ and cytotoxic ____
3. once those receptors are engaged, the APC will also start to secrete ____ (not shown on this slide), that will result in full activation of this naiive T-cell.
-so essentially, we’re starting off with CD8 positive cell that has never been stimulated by antigen
it’s gotten out into peripheral circulation, has bumped into APC. (in this context, acts as target for
cytotoxic T cell)
-its gonna process and present viral peptides on surface of target cell, in the context of the self-class I
molecule that can now be recognized by the antigen receptor on the surface of the naiive T cell -so that’s signal 1.

Answer 27

2
antigen
APC
T Cell
cytokines

Question 28

Cytotoxic T Cells

once CD8 positive cell is fully activated and becomes an effector cell, it can actually kill target cells via 2 potential mechanisms: first is it comes along and bumps into target cells that have viral antigens processed and presented on its cell surface in the context of ____ molecules. they recognize this complex and don’t require any other signals. upon recognition of this complex, they release contents of cytoplasmic ____ that are found inside a mature cytotoxic T cell. within these granules are molecules designated ____, and another designated granzymes.
-perforin - forms ____ in target cell plasma membrane (PM), and so other contents of granules found in the cytoplasm, can now find its way inside the target cell. these molecules would initiate the activity of ____, that are involved in the induction of ____

-ultimately, the target cell dies. so this mechanism requires the formation of ____ in the target cell membrane.
subsequently, the intro of T-cell derived molecules that induce the activation of the ____. -so this is first mechanism, which is shown here in this below pic.

Answer 28

self class I
granules
perforins
pores

caspases
apoptosis

pores
apoptotic cascade

Question 29

Cytotoxic T Cells

red dots = peptides from viral proteins (expressed on ____ expressed via self class I molecules)

complement mediated killing of cells > pore formation, but the cells die via ____; release intracellular contents into extracell space > inducing ____ rxn > tissue destruction

apoptosis via cytotoxic T cells > no release of ____ > minimal tissue destruction associated

Answer 29

osmotic lysis
inflammatory

internal material

Question 30

Cytotoxic T Cells

CTL granules contain numerous effector molecules including ____ and ____

the number of pores produced via this CTL process is largely diminished compared to ____ mechanism

Answer 30

perforin
granzymes
complement

Question 31

Cytotoxic T Cells

Two mechanisms for killing target cells

B) expresses Fas on the ____; FasL on the ____ binding Fas > induces activation of ____ on target cell (no ____ of T cell); still requires recognition of ____ peptide in self class I molecule

perforin/granzyme is more ____; not all target cells express Fas

Answer 31

target cell
T cell
apoptosis
granulation
viral
common

Question 32

Cytotoxic T Cells in Immune Reactions Against Tumors

1) tumor cell expresses mutated self-proteins > tumor cells are ____ (express class I), the proteins will be recgonized by T cells with the appropriate antigen receptor
2) ____ encodes a unique protein that is present on the self class I molecule (different from what your normal genome encodes)
3) tumor cells express normal cell proteins that are normally express at low levels, but they become ____ as a result of transformation
4) certain viruses are ____ > induce transformation on part of own cell

the mechanisms of killing is via ____ formation or via ____ if the tumor cell expresses Fas on the surface

Answer 32

nucleated
oncogene
overexpressed
ongogenic

pore
Fas

Question 33

Cytotoxic T Cells in Immune Reactions Against Tumors

left: techniques that treat cancer that involve induction of cytotoxic T cell response > isolate patients T cells > mix tumor with T cells in a petri dish > induction of activation of ____ cells > grow them and infuse back into patient, with the notion that these cells will specifically the target the cells they’ve been stimulation against
right: isolate tumor, mix with ____ (potent APC) and inject back into patient as a vaccine; vaccine stimulates cyto T cells that will find and kill tumor

genetically engineer cells that has a ____ that recognizes antigens on the tumor cell (____ therapy)

Answer 33

cyto T
dendritic cells
receptor
CART

Question 34

Functions of TH1 and TH2 Cells

Classically, the TH1 subset is associated with ____ immunity and the TH2 subset with ____ immunity. However, the two subsets are involved in ____ types of immune responses.

TH1: classically, associated with induction of cell-mediated forms of immunity (activation of cyto T cells, macros, NK

TH2: classically, associated with humoral immune responses

classically: cells that would interact with B cells would come from TH2 subset; CD4+ is TH1 positive, that activates cytotoxic T cells

now, TH1 subset is involved in cyto t cells, activation of macrophage, BUT ALSO fine tunes the ____ immune responses; TH2 subset capable of activating ____ (a form of cell mediated immunity)

not absolute: both subsets have the capacity of being involved in ____ and/or ____ mediated immunity

Answer 34

cell-mediated
humoral
both

humoral
eosinophils

humoral
cell