T Cells (complete)

Question 1

What are the 6 main types of T cells?

Answer 1

1) Th1
2) Th17
3) Th2
4) Tfh
5) Treg
6) CTL

Question 2

Describe Th1 cells

Answer 2

• Secrete lymphokines (IFN-gamma) when they encounter Ag

Think: pro-inflammatory and chemotactic

• Monocytes and macrophages move in and are activated by IFN-gamma (macrophages get ANGRY)
• macros kill invaders

Question 3

Describe Th17 cells

Answer 3

Makes pro-inflammatory lymphokine IL-17

• Resembles Th1 (b/c its main job is inflammation)
• Implicated in several autoimmune disorders
• ANGRIER macrophages

Question 4

Describe Th2 cells

Answer 4

• Circulate in blood until encounter Ag
• Secrete IL-4 and IL-13 (attract/activate macrophages)
• Involved in HEALING
• Produces IgE (see IL-4 flashcard)

Question 5

What does IL-4 do?

Answer 5

• Chemotactic for eosinophils (kills worms/protozoans)
• if secrete from Th2-like follicular cells in lymphoid tissue, IL-4 pushes B cells to switch from IgM/IgG to make IgE (Ab of parasite resistance)

Question 6

Describe Thf

Answer 6

• Dendritic cell arrives in lymph node —-»> thf to migrate into follicles of lymph cortex where B cells are
• Help B cells that recognize Ag become activated

Secrete cytokines which:

1) in gut, switch B cells to IgA
2) in spleen, switch to IgG
3) other places, switch to IgE

Question 7

Describe Tregs

Answer 7

5% of T helper cells

• Suppress activation/function of other T helper cells (1 for every 1000 Th cells)
• Most are CD4+/CD5+
• Produce TGFbeta and IL-10

Question 8

Describe CTLs

Answer 8

cytotoxic killer T cells —» signal to target cell to commit suicide (apoptosis)

Two methods:

1) activate Fas (CD95) death receptor
2) secretes contents of lytic granules containing proteases —» penetrate target cell (apoptosis)

Question 9

Define cytokine

Answer 9

Short range mediators

Made by any cell

EX: IL-1, TNFalpha, IL-12

Question 10

Define lymphokine

Answer 10

Short range mediators

Made by lymphocytes

Subset of cytokines

EX: IL-2, IFNgamma, IL-4, IL-5, IL-10

Question 11

Define chemokine

Answer 11

Small (6-14kD) short range mediators

Made by any cell that causes inflammation

EX: MIP-1 to 4, Rantes, CCL28, CXCL16

Question 12

What is the main lymphokines made by Th1? What is its function?

Answer 12

IFN-gamma

• Pro-inflammatory
• chemotactic for blood monocytes (become macros)
• Macros activated by IFN-gamma —» ANGRY

Question 13

What is the main lymphokines made by Th2? What is its function?

Answer 13

IL-4

• Attracts/activates macros
• chemotactic for eosinophils

Question 14

What is the main lymphokines made by Th17? What is its function?

Answer 14

IL-17

• Causes inflammation
• Implicated in several autoimmune diseases

Question 15

What is the main lymphokines made by Treg? What is its function?

Answer 15

IL-10

• Downregulates Th1 and Th2

Question 16

Describe how Tfh cells help B cells get activated by antigen and switch immunoglobulin class

Answer 16

• B cell binds to Ag epitope —» endocytoses it
• Breaks up Ag in vesicle
• Peptide fragmts bind to MHC class 2 and brought to surface
• Tfh see this epitope/MHC complex
• Tfh bind and secrete lymphokines and ACTIVATE B cell!
• Signals tell B cell which Ig to secrete

Question 17

Define mitogen

Answer 17

Protein that stimulates cell division (mitosis)

They trick the T cells into thinking it’s Ag b/c they bind to CD3s (on almost all cells)

Question 18

What are suggested uses for B and T cell mitogens in the clinical lab?

Answer 18

In order to see a person’s karyotype you need dividing cells (to see metaphase!!!)

Question 19

Distinguish between the effects of a mitogen (mg) and an Ag when added to normal blood lymphocytes

Answer 19

Ag = specific
Mg = non-specific

Mg doesn’t actually bind to Ag sites — it binds to CD3 which signal all pathways (like it bypasses one step)

Question 20

Compare B cell and T cell receptors

Answer 20

Have V(D)J regions in CDRs — also common and variable portions

Question 21

Contrast B cell and T cell receptors

Answer 21

T: interact w/ cell surfaces

• 2 chains (alpha and beta), each w/ 3 CDRs
• both alpha/beta have transmembrane domains

B: interacts w/ free Ag

• 4 chains, each w/ 3 CDRs
• only heavy chains are transmembrane

Question 22

Describe the structures recognized by T cell receptors

Answer 22

TCRs recognize very specific Ag peptides and MHC on cells

Question 23

How is Ag recognition by helper and cytotoxic T cell receptors different?

Answer 23

Helper: TCRs work w/ CD4 to bind Class 2 MHC + Ag

CTL: TCRs work w/ CD8 to bind Class 1 MHC + Ag

Question 24

Explain the role of dendritic cells in the process of T cell receptor recognition

Answer 24

When a T helper cell binds to an Ag producing cell (APC), the DC gives an “activating boost” by secreting cytokines

Question 25

Describe MHC-restricition

Answer 25

• T cells are MHC restricted in Ag recognition to cells that are genetically identical to them

REMEMBER: they don’t “see” Ag alone, only Ag presented in MHC (have to recognize “self”)

Question 26

Describe the role of T cells in ridding the body of viral infection

Answer 26

CTLs see an APC infected w/ virus (remember: via MHC class 1 + Ag) — begins apoptosis signaling

Helpers see a DC, B cell or macro infected w/ virus (remember: via MHC class 2 + Ag) — activate and divide

Question 27

Describe the characteristics of T-independent Ags

Answer 27

Pretty much don’t need T cells to activate an immune response

• Ags = molecules w/ same epitope repeated often — rare in proteins, common in carbs (e.g. Strep)
• Ab response is almost all IgM (T cells needed for the switch)

Question 28

Outline an experiment that shows that an Ab response is T-dependent

Answer 28

expose cells to Ags and see what Abs respond

If only IgM = T independent

If more = T-dependent