T Cells (complete) Flashcards
What are the 6 main types of T cells?
1) Th1
2) Th17
3) Th2
4) Tfh
5) Treg
6) CTL
Describe Th1 cells
- 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
Describe Th17 cells
Makes pro-inflammatory lymphokine IL-17
- Resembles Th1 (b/c its main job is inflammation)
- Implicated in several autoimmune disorders
- ANGRIER macrophages
Describe Th2 cells
- Circulate in blood until encounter Ag
- Secrete IL-4 and IL-13 (attract/activate macrophages)
- Involved in HEALING
- Produces IgE (see IL-4 flashcard)
What does IL-4 do?
- 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)
Describe Thf
- 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
Describe Tregs
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
Describe CTLs
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)
Define cytokine
Short range mediators
Made by any cell
EX: IL-1, TNFalpha, IL-12
Define lymphokine
Short range mediators
Made by lymphocytes
Subset of cytokines
EX: IL-2, IFNgamma, IL-4, IL-5, IL-10
Define chemokine
Small (6-14kD) short range mediators
Made by any cell that causes inflammation
EX: MIP-1 to 4, Rantes, CCL28, CXCL16
What is the main lymphokines made by Th1? What is its function?
IFN-gamma
- Pro-inflammatory
- chemotactic for blood monocytes (become macros)
- Macros activated by IFN-gamma —» ANGRY
What is the main lymphokines made by Th2? What is its function?
IL-4
- Attracts/activates macros
- chemotactic for eosinophils
What is the main lymphokines made by Th17? What is its function?
IL-17
- Causes inflammation
- Implicated in several autoimmune diseases
What is the main lymphokines made by Treg? What is its function?
IL-10
- Downregulates Th1 and Th2
Describe how Tfh cells help B cells get activated by antigen and switch immunoglobulin class
- 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
Define mitogen
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)
What are suggested uses for B and T cell mitogens in the clinical lab?
In order to see a person’s karyotype you need dividing cells (to see metaphase!!!)
Distinguish between the effects of a mitogen (mg) and an Ag when added to normal blood lymphocytes
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)
Compare B cell and T cell receptors
Have V(D)J regions in CDRs — also common and variable portions
Contrast B cell and T cell receptors
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
Describe the structures recognized by T cell receptors
TCRs recognize very specific Ag peptides and MHC on cells
How is Ag recognition by helper and cytotoxic T cell receptors different?
Helper: TCRs work w/ CD4 to bind Class 2 MHC + Ag
CTL: TCRs work w/ CD8 to bind Class 1 MHC + Ag
Explain the role of dendritic cells in the process of T cell receptor recognition
When a T helper cell binds to an Ag producing cell (APC), the DC gives an “activating boost” by secreting cytokines
Describe MHC-restricition
- 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”)
Describe the role of T cells in ridding the body of viral infection
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
Describe the characteristics of T-independent Ags
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)
Outline an experiment that shows that an Ab response is T-dependent
expose cells to Ags and see what Abs respond
If only IgM = T independent
If more = T-dependent
