30.3 - Defence Against Infectious Disease_Specific Immune Response Flashcards
Why is a specific antigen recognition system required?
To minimise collateral damage to tissues - since many proteins may be very similar between pathogens and eukaryotic cells.
How are antigens distributed?
Clonogenically.
What is the definition of clonogenicity?
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.
How is antigen diversity generated in T and B cells?
T-cells
* V(D)J Recombination.
B-cells
* V(D)J Recombination
* Somatic Hypermutation.
* Class Switch Recombination.
How are antigens presented to B/T cells?
- 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).
What does a lymphocyte do when it recognises an antigen?
Selection, clonal expansion, differentiation.
Describe the immunological memory for a specific antigen.
The secondary response is faster and more effective.
Why is the secondary immune response more effective than the primary immune response?
The memory B cells have a higher antibody affinity due to somatic hypermutation
What are the two types of adaptive immune response?
- Humoral immunity - production of antibodies
- Cell mediated immunity - killing pathogens directly
What cell types do activated B-cells differentiate into?
memory cells and Ab secreting plasma cells.
Overall what are the four main roles of antibodies?
- Prevention of pathogen entry (e.g. viruses + mucosal bacteria)
- Neutralisation of toxins
- Opsonisation of bacteria
- Activation of complement (to initiate acute inflammation)
What T-cell types are there?
- CD4 T-helper (Th) cells.
*CD8 cytotoxic (Tc) cells.
What is the role of Tc cells?
They directly kill virus infected and tumour cells.
What is the role of the cytokines secreted by T cells?
Activation of macrophages and NK cells to improve the effectiveness of innate immunity.
How are T-cells involved in antibody class switching?
CKs secreted by the T-cells can induce class switching to different Ab isotypes.
* IL-4 -> IgE
*IFN-gamma -> IgG2a
*TGF-beta -> IgA
How do Th-cells activate B cells?
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
Where does T-cell activation of B cells take place?
In the lymph node germinal centres.
What is autoimmunity caused by?
Breakdown of immune tolerance.
