T-Cell Diversity

Question 1

Define T-cells and where they are formed.

Answer 1

Lymphocytes that express T-cell antigen receptors (TCR’s); formed in the thymus.

Question 2

What do T-cells secrete and what do these secretions control?

Answer 2

Cytokines: Induce changes in cells, especially the differentiation of B cells into Plasma cells… these secretions control –> Cytotoxins: (Kill [infected] cells via the adaptive immune response.)

Question 3

What antibody is associated with B-cells, and with Plasma Cells?

Answer 3

B cell = IgM ; Plasma cell = IgG

Question 4

What is the Immunologic Synapse? What secretion is it associated with?

Answer 4

Space that allows for communication between T-cell and Target cell; associated with cytotoxins.

Question 5

Define DiGeorge Syndrome.

Answer 5

Lack of a thymus due to a mutation in the transcription factor causing T-cell deficiency. (Susceptible to viral/bacterial/fungal/parasitic infections.)

Question 6

Why would the lack of T-cells cause susceptibility to viruses?

Answer 6

Because Cytotoxic T-cells kill virus infected cells and Helper T cells provide cytokines to B-cells that allow them to make neutralizing antibodies against viruses.

Question 7

Why does lack of T-Cells cause susceptibility to Pygogenic (pus inducing) Bacteria? Intracellular Bacteria?

Answer 7

T-cells are essential for B-cell responses (to eliminate bacteria);
T-cells make cytokines (interferon-gamma) that activate macrophages to kill intracellular bacteria.

Question 8

About how many different T-cells are there in Humans? TCR’s?

Answer 8

10^12 ; 10^10

Question 9

Where does V(D)J recombination generating T cell diversity occur? How does this contrast to B cell diversity?

Answer 9

In the thymus only; B cells diversify in Bone Marrow and the Periphery in a process called Affinity Maturation.

Question 10

Irreversible genomic rearrangement occurs where?

Answer 10

At the alpha & beta loci (each lymph gets a unique Ab receptor).

Question 11

What exactly are the alpha and beta loci?

Answer 11

They are each arm of the dimer receptor.

Question 12

When does diversity of T-cell receptors occur, before or after encountering antigens?

Answer 12

Before, so your body is ready.

Question 13

List the mechanisms for generating TCR diversity.

Answer 13

Each TCR has 2 chains (products of V(D)J). Multiple variable domain exons. Multiple diversity/joining segments. Imprecision in the joining process (nucleotides added/deleted– N region diversity).

Question 14

Which molecule transmits T-cell receptor signals?

Answer 14

CD3 - once TCR binds to Ag, this molecules signals cell to react

Question 15

What antigens do T-cells see?

Answer 15

MHC molecules loaded with peptides.

Question 16

What are MHC molecules?

Answer 16

Cell surface proteins encoded by a genomic locus known as the Major Histocompatibility Complex

Question 17

What is another name for MHC molecules in humans?

Answer 17

Human Leukocyte Antigens (HLA molecules)

Question 18

Which MHC class has only 1 membrane penetrating chain and is slightly smaller?

Answer 18

MHC class 1.

Question 19

What peptides are presented by MHC molecules?

Answer 19

Short (8-17 AA) peptides that come from the degradation of self or foreign proteins.

Question 20

Where are these peptides generated?

Answer 20

Either the cytosol or in the endocytic compartments that retrieve proteins from outside cells.

Question 21

What is the only way a T-cell receptor recognizes anything?

Answer 21

When it encounters a MHC – Peptide complex (not individually).

Question 22

MHC Class, CD4/CD8?

Answer 22

CD4 T-Cell: Class II

CD8 T-Cell: Class I

Question 23

Type of T-Cell, CD4/CD8?

Answer 23

CD4 T-Cell: Helper T-Cell

CD8 T-Cell: Cytotoxic T-Cell

Question 24

On which type of cells, CD4/CD8?

Answer 24

CD4 T-Cell: Dendritic/B/Macrophage

CD8 T-Cell: All nucleated cells

Question 25

Peptides from, CD4/CD8?

Answer 25

CD4 T-Cell: Outside cells (serum)

CD8 T-Cell: Inside cells (cytosol)

Question 26

Helper T cells secrete? Cytotoxic T cells kill?

Answer 26

Cytokines; Kill virus infected cells

Question 27

What is the difference between B and T cells regarding Antigen receptors and recognition?

Answer 27

T-cell: Receptor is T-cell receptor (TCR)-only found on cell surface
B-cell: Receptor is Antibody molecule - can be on cell surface or cell free in the serum

T-cell: Recognizes only cell bound antigens (MHC-peptide complexes)
B-cell: Recognizes cell bound or cell free (serum) antigens.

Question 28

Which cell does not undergo Affinity maturation/hypermutation?

Answer 28

T-cells

Question 29

What happens in Bare Lymphocyte syndrome?

Answer 29

Patients are unable to express MHC class II molecules and thus CD4 T cells fail to develop and antigens can’t be recognized.

Question 30

How is Clonal Expansion critical for the immune response?

Answer 30

The production of daughter cells (arising from one cell) with specific antigen receptors can eliminate the pathogen quickly.

Question 31

List the 3 key steps in an immune response.

Answer 31

1. Antigen recognition and T cell activation (signaling by CD3)
2. Proliferation of antigen-specific T cells (TCR signaling induces rapid expansion of T-cells specific for new pathogen)
3. Differentiation of antigen-specific T cells into Effector cells:
   a. Proliferating T cells can make Cytokines/Cytotoxins
   b. Some T-cells become Memory cells for future pathogen encounters

Question 32

What do CD4 T cells differentiate into?

Answer 32

A) TH1 effector cells-Macrophage/B cell activation, production of opsonizing antibodies such as IgG

B) TH2 effector cells-General activation of B cells to make Ab’s

Question 33

What does Th1 secrete? What is it essential for?

Answer 33

Interferon y – activates macrophages

IL-2 – promotes T cell growth, other cytokines

*Essential for resistance against intracellular bacteria.

Question 34

What does Th2 secrete? What is it essential for?

Answer 34

IL-4 – causes B cell growth and differentiation (for IgE production)

IL-5 – causes B cell/eosinophil differentiation, other Cytokines (IL-13)

*Essential for resistance against worms and other parasites.

Question 35

What do CD8 T-cells differentiate into?

Answer 35

Cytotoxic T cells (with lytic granules).