Lymphocytes Flashcards
What do lymphocytes stem from?
Common lymphoid progenitor cell
What types of immune response are there and which lymphocytes correspond?
Humoral - B Cells, use antibodies
Cell-Mediated - T Cells, use cytokines
What are antigens?
Proteins on cell surface membranes used to identify cells, and to know if they are self cells or foreign
What is an epitope?
The part of an antigen which an antibody binds to
What is the problem with antigen diversity?
To respond to all of the different antigens our bodies would require a large pool of cells with specific receptors but as specificity increases, diversity decreases
How is antigen receptor diversity generated?
Immunglobulin gene rearrangement:
- Each BCR chain is encoded by separate multigene families on different chromosomes
- When B Cells mature the gene segments arrange is a random order
What is the structure of a T cell receptor?
A part of a complex of proteins on the cell surface membrane
What do T cell receptors detect?
Linear epitopes(fragments of proteins made by other cells)
What do MHCs do?
They present antigens to T cells
What gene encodes MHCs?
HLA genes
Where are MHC class 1 found?
On all nucleated cells
Where are MHC class 2 found?
On antigen presenting cells
How do MHC class 1 work?
They are on the surface of cells and are constantly presented with proteins produced from inside the cell so the body knows what antigens are self
Viruses cause the cell to produce viral proteins and this it detected by MHC1 receptors
How do MHC type 2 work?
They are present on dendritic cells and travel around the body
If they come into contact with infectious material they engulf it, break it down and present the antigen on the MHC2
What cells do MHC1 interact with?
CD8 killer T cells
What cells do MHC2 interact with?
CD4 T cells
What are CD4 cells?
T-helper cells
What are CD8 cells?
Cytotoxic T-killer cells
How do CD8 cells work?
They contain perforin which punctures a hole in the membrane of a bad cell and then granzymes are injected to stimulate apoptosis of the cell
What do CD4 cells do?
They contain cytokines which stimulate other immune cells in the body to react to the infection
What is the function of B cells?
They make antibodies is response to soluble antigens detected
Require help from other cells to produce antibodies
What is the structure of antibodies?
They have a main heavy chain and a light chain
These chains are both made up of variable and constant regions
What are the classes of antibody?
IgG, IgA, IgE, IgD and IgM
What is the function of antibodies?
Nerutralisation:
Bind to pathogens and prevent them from communicating to and entering cells
Opsonisation:
Surround pathogen which promotes phagocytosis
Complement activation:
Enzymatic cascade leading to cell death
What is the structure of BCRs?
They are antibodies on the cells surface
What signals can a B cell receive to produce antibodies?
- Signals directly from microbial constituents
- Signals from a T helper cell (CD4)
What are thymus independent antigens?
Antigens that directly activate B cells without the help of T cells
They have a repeating structure, cause B cell to clump together
Second signal is provided by microbial constituent or an accessory cell
It isnt very strong
How do T cells activate B cells?
- Dendritic cells and B cells both detect and engulf pathogens
- They present the antigen on their MHC2 recptors
- The dendritic cell then activates the T helper(CD4) cell
- The active CD4 cell then goes and activates the B cell
- The B cell matures into a plasma cell and produces antibodies
