3.2 T Cell Antigen recognition

Question 1

The T-Cell family

Answer 1

CD4 TM 1 cells

• > Activate infected macrophages.
• > Provide help B cells for antibody production

-> Microbes that persist in macrophage vesicles (e.g. myobacteria, Listeria, Leishamania, donovani, Pneumocystis carini) Extracellular bacteria

CD4 TM 2 cells

• > Provide help to B cells for antibody production, especially switching to IgE.
• > Helmith parasites

Question 2

The T-Cell family continued ….

Answer 2

Macrophages

• > NK / NKT cells
• > alpha / beta T cells

Dendritic cell with naive T cells
=> (TGF beta) -> Treg (Tolerance Autoimmune Tumor escape)
=> (IFN - gamma / IL-12) -> TC1 (Perforin Granzyme) / TH1 (IFN-gamma / IL-1 / TNF - alpha) -> Anti tumor / anti infection / autoimmune
=> (TGF - beta / IL-23 / IL-6) -> TH 17 (IL-17) -> Anti-infection / autoimmune
=> (IL-4 / IL-5) -> TH2 (IL-4 / IL-13 / IL-5 / IL-6) -> Anti-infection / allergy / asthma

Question 3

T-Cell receptor

Answer 3

alpha and beta chain (carbohydrate attached) along with cytoplasmic tail connected by a disulfide bond.

• > Viariable region V
• > constant region C
• > stalk segment
• > transmembrane region

Clonal receptor
1 T cell – 1 specificity of TCR

Heterodimeric receptor (110 amino acids)
- Alpha / Beta or Gamma / Delta

α chain (40 - 50 kDa) / β chain (35 – 47 kDa)

• Majority of T cells in the peripheral blood
• γ / δ T cells found almost exclusively in submucosa

T Cell complementary-determining region CDR is the equivalent of antibody hypervariable region

Question 4

T-Cells - Key facts

Answer 4

-> Most abundant type of lymphocyte

• > Originate in BM – educated in Thymus Naïve, mature T cells are either:
  - TCR & CD4+ve (helpers) - make cytokines
  - TCR & CD8+ve (cytotoxics) – lyse virally infected/tumour cells

Question 5

Major Histocompatability Class (MHC) II

Answer 5

Function:
to present peptide antigens

-> CD4 & CD8 are required to mount an effective response to antigen

Question 6

The T-Cell family

Answer 6

CD8
-> CD8 cytotoxic T-Cells

CD4

• > CD4 TH 1 / 2 / 17 cells
• > TFH cells
• > CD4 regulatory T-cells (various types)

T cell expressed co-receptors
Bind to MHC molecule but not where the peptide antigen is!

Question 7

Processed and presented

Answer 7

CD8 T cell

• > T-cell receptor (alpha + beta)
• > antigen (surrounded by alpha 1 + alpha 2)
• > Beta 2 microglobulin (Beta + Alpha 3 acting as target cell)

CD8 T cell
-> Alpha + Beta = CD8

B Cell with antigen

Question 8

T cell activation requires a plethora of molecules

Answer 8

APC to T-Cell

• > IL - 1 / 6 / 12 / 15
• > TNF alpha

T-Cell to APC

• > IFN gamma
• > GM - CSF
• > IL - 4
• > TNF beta
• > CD2 - LFD 3 (CD48)
• > LFA 1 - ICAM 1
• > TCR - Class II (p56Lck with CD4)
• > CD28 - B7 1 / B7 2 (CD80 / CD86)