Cellular Immunity and Histocompatibility Flashcards
(46 cards)
What are the two things that the T lymphocytes express
CD4 and CD8 surface antigens
What is CD4
Helper T cell that respond by secreting cytokines
What do T lymphocytes encounter on thymic epithelium
MHC class 1 and MHC class 2
What happens if a T lymphocyte responds to MHC class ll
They become CD4 helper T cells
What happens if a T lymphocyte responds to MHC class l
They become CD8 cytotoxic T cells (CTL)
What is CD8
Cytotoxic - they kill all other infected cells
What percentage of blood T cells are each CD4 and CD8
CD4 - 80%
CD8 - 20%
What are the functional subsets of CD4 helper T cells
Treg, Th1, Th2, Th17
What does Treg do
Suppresses the immune response
What does Th1 do
Promotes cell-mediated immunity
What does Th2 do
Promotes antibody mediated immunity
What does Th17 do
promotes inflammation
What is the thymus and where is it located
The thymus is a primary lyphoid organ that is largest at birth and shrinks with age. It sits at the top of the percardium above the heart.
Haemapoietic lymphoid precursors
Migrate from the bone marrow to the thymus where they mature into T lymphocytes
What is a viral infection
Infects epithelial tissue and replicates inside cells.
What are viral infections regulated by
A set of highly polymorphic genes that were first identified as controlling tissue transplantation.
What is a T cell receptor (TcR)
It is an Ig molecule on the surface of all T lymphocytes
What does the TcR gene locus undergo
Rearrangement (just like B cells)
What does the TcR recognise, and why
Only one antigen - which are the proteins of the Major Histocompatibility Complex (MHC) because the T cells were ‘selected’ during thymic development for their ability to respond to self MHC molecules
Does the TcR undergo affinity maturation or not, and why?
It does not undergo affinity maturation because you dont want the affinity of TcR to increase to a self-antigen (MHC)
How do T cells recognise foreign antigens from both virus and bacteria
Only when there are presented by MHC molecules on the surface of cells. This is how they detect host cells that have become virally infected.
How do T cells pick up viral infections
They detect small fragments of virus picked up inside the cell and expressed in the binding groove of MHC molecules on the cell surface.
MHC restriction means that T cells can see what two antigens at the same time?
- Foreign peptide antigen (non-slef) imbedded in MHC
- MHC molecules (self)
Describe how and why TcR has affnity towards the combination of MHC
The antigen binding surface of the TcR (top molecule) binds to the top of MHC which represents the ‘peptide groove’ containing the foreign peptide antgien. Thus the TcR has affinity towards the combination of MHC.
