Inflammatory Bowel Disease Flashcards
What is the innate immune system?
First response to infection
What are the 3 main components of the innate immune system?
- Toxic/inhibitory substances
- Complement system
- The cells that make up the innate part
What are examples of toxic/inhibitory substances?
- Enzymes e.g. lysozymes in tears
- C-reactive protein (CRP)
What does CRP do?
Enhances phagocytosis and complement binding
What is the complement cascade?
A series of proteins in blood which, when activated, promote inflammation, opsonisation and lysis of pathogens
What are the cellular components of the innate immune system?
- Phagocytes (neutrophils, monocytes/macrophages, dendritic cells, eosinophils)
- Mast cells & basophils (release mediators (e.g. histamine when activated)
- Natural killer cells
Why is the innate immune system insufficient protection?
Rapid response
BUT
- No memory formation
- Recognises limited numbers of sites on foreign organisms
Where are B cells produced/matured?
Produced and matures in bone marrow
What is life cycle of B cells?
Produced throughout life, survive only a few days
How do B cells work?
- Have antibodies on their surface which act as antigen receptors
- When activated proliferate and differentiate into plasma cells producing specific antibody
- Memory cells formed
Where are T cells produced/matured?
Produced in bone marrow and matures in thymus
What is life cycle of T cells?
Most produced before puberty, so long-lived
How do T cells work?
Have T cell receptors with variable regions which recognise presented antigens
Memory cells are formed
What are the different types of T cells?
Distinguished by proteins expressed on surface:
- CD4+ (Helper T cells)
- CD8+ (cytotoxic T cells)
Also regulatory T cells (Treg)
How do B and T cells interact?
- Activated B cell engulfs and digests antigen
- B cell displays antigen fragments bound to its unique MHC molecules
- Combination of antigen and MHC attracts matching T cell
- Cytokines secreted by T cell help B cell to multiply and mature into antibody producing plasma cells
What is MHC?
Major Histocompatibility Complex is a region on chromosome 6 coding for proteins involved in immune function
Includes genes for proteins on cell surfaces which have a cleft that holds a small peptide derived from proteins within the cell (HLA)
Where is MHC class I found?
On all nucleated cells
What does MHC I display in healthy cells?
display fragments of normal intracellular proteins
What does MHC I display in infected cells?
display fragments of bacterial or viral protein
Where is MHC class II found?
Found on antigen presenting cells (APCs) – macrophages, dendritic cells, B-lymphocytes
What does MHC II display?
fragments of internalised antigens
What does CD4 facilitate the binding of?
T helper cells to MHC II
What does CD8 facilitate the binding of?
Cytotoxic T cells to MHC I
What are the 3 different types of T helper cells (CD4+ lymphocytes)?
- Th1
- Th2
- Th17
