Basic Science Flashcards
Tolerance
Failure of the immune system to respond in an aggressive way (meaning, not attacking self)
Where does early tolerance occur (central tolerance)
In the bone marrow and thymus. Most B and T cells die before becoming self-reactive
Negative selection
Process of controlling auto reactive cells. B cells express IgM on their surface and BCR recognizes this within the bone marrow which triggers their apoptotic death
How else does negative selection occur
Binding of an MHC complex and TCRs (CD4 and CD8) also causes apoptotic death
Peripheral tolerance
Process of controlling autoreactive cells as they exit the bone marrow or thymus. Via anergy or suppression.
T cell responses are….
Cell-mediated
What are the 2 classes of T cells
Cytotoxic and helper T cells
How can you classify T cells
Based on the presence of CD4 and CD8 proteins on their plasma membranes
What protein do cytotoxic T cells have on their membrane
CD8
What protein do helper T cells have on their membrane
CD4
What are cytotoxic T cells (CD8) good in fighting off
Bodies own cells that have become cancerous or are infected with virus (or some bacteria that resides in a host cell)
How do cytotoxic T cells work
“Attack” cells. Bind to target (antigen) and directly kill them via secreted chemicals. These cells see CYTOSOL derived peptides on an MHC I cell and kill it.
What is the role of helper T cells (CD4)
They activate B cells, macrophages and cytotoxic T cells (via secretion of cytokines). Bind with MHC II cells
How do helper T cells work with B cells
- B cells are bound to an antigen.
- They then present this antigen to a helper T cell (helper T cell also bound to an antigen to be activated)
- T cell then makes contact with the B cell via BCRs which induces B-cell activation (and thus antibody secretion). Cytokines play a big role in this activation
Of note: Dendritic cell packages the antigen and presents it to the helper T cell (all going on at the same time as the B cell/antigen interaction)
How do helper T cells activate cytotoxic T cells
- Activated helper T cell first helps other cells (i.e. dendritic cells)
- These dendritic cells then activate cytotoxic T cells
Basically the CD4 cell in this case indirectly helps the cytotoxic T cell via dendritic cells
How do helper T cells activate macrophages and neutrophils
Via different types of cytokine secretion
What is the difference between T cell receptors and B cell receptors
- T cell receptors remain on the T cell membrane where as antibodies are secreted.
- T cell receptor cannot combine with an antigen unless the antigen is complexed with plasma membrane proteins
What does the T cell receptor bind with
Both the antigen complex and the body protein
What does MHC stand for
major histocompatibility complex
What is the MHC
A group of proteins that come from the plasma membrane of a cell that must be complexed with the antigen in order for T cell recognition to occur
What are the 2 classes of MHC proteins
I - CD8 (cytotoxic)
II - CD4 (helper)
Where are class 1 MHC proteins found
All cells except RBC
Where are class 2 MHC proteins found
Mainly on the surface of macrophages, B cells and dendritic cells
MHC + antigen(once packaged in cell) =
Antigen presenting cells (APCs)
How do T cells detect antigens
They detect them when they are bound to an MHC
Macrophages, B cells and dendritic cells are APCs for what T cell
Helper T cell (CD4)
Helper T cells are the link between
Innate and adaptive immunity