30.3 - Defence Against Infectious Disease_Specific Immune Response

Question 1

Why is a specific antigen recognition system required?

Answer 1

To minimise collateral damage to tissues - since many proteins may be very similar between pathogens and eukaryotic cells.

Question 2

How are antigens distributed?

Answer 2

Clonogenically.

Question 3

What is the definition of clonogenicity?

Answer 3

The ability of cells from multicellular organisms (e.g., malignant cells or stem cells) to proliferate and form colonies (or clones), each consisting of one or more cell types. A cell with this ability is called a clonogenic cell.

Question 4

How is antigen diversity generated in T and B cells?

Answer 4

T-cells
* V(D)J Recombination.
B-cells
* V(D)J Recombination
* Somatic Hypermutation.
* Class Switch Recombination.

Question 5

How are antigens presented to B/T cells?

Answer 5

• B-cells: recognise a wide variety of native antigens.
  *T-cells - recognises short peptide segments of protein antigens presented by MHC molecules on APCs (e.g. macrophages/ B-cells/ dendrites).

Question 6

What does a lymphocyte do when it recognises an antigen?

Answer 6

Selection, clonal expansion, differentiation.

Question 7

Describe the immunological memory for a specific antigen.

Answer 7

The secondary response is faster and more effective.

Question 8

Why is the secondary immune response more effective than the primary immune response?

Answer 8

The memory B cells have a higher antibody affinity due to somatic hypermutation

Question 9

What are the two types of adaptive immune response?

Answer 9

• Humoral immunity - production of antibodies
• Cell mediated immunity - killing pathogens directly

Question 10

What cell types do activated B-cells differentiate into?

Answer 10

memory cells and Ab secreting plasma cells.

Question 11

Overall what are the four main roles of antibodies?

Answer 11

• Prevention of pathogen entry (e.g. viruses + mucosal bacteria)
• Neutralisation of toxins
• Opsonisation of bacteria
• Activation of complement (to initiate acute inflammation)

Question 12

What T-cell types are there?

Answer 12

• CD4 T-helper (Th) cells.
  *CD8 cytotoxic (Tc) cells.

Question 13

What is the role of Tc cells?

Answer 13

They directly kill virus infected and tumour cells.

Question 14

What is the role of the cytokines secreted by T cells?

Answer 14

Activation of macrophages and NK cells to improve the effectiveness of innate immunity.

Question 15

How are T-cells involved in antibody class switching?

Answer 15

CKs secreted by the T-cells can induce class switching to different Ab isotypes.
* IL-4 -> IgE
*IFN-gamma -> IgG2a
*TGF-beta -> IgA

Question 16

How do Th-cells activate B cells?

Answer 16

3 signals required:
1. TCR/ BCR interaction - with MHC/ antigen peptide or just the Antigen.
2. Co-stimulatory molecules (e.g. CD40(L))
3. CKs

Question 17

Where does T-cell activation of B cells take place?

Answer 17

In the lymph node germinal centres.

Question 18

What is autoimmunity caused by?

Answer 18

Breakdown of immune tolerance.