Immunology 2: cell mediated immunity Flashcards
What is cell mediated immunity?
The form of adaptive immunity that is mediated by T lymphocytes
What are the two major types of T lymphocytes?
- Around 2/3 of T lymphocytes express CD4, and are called CD4+ T cells
- the other 1/3 of T lymphocytes express CD8 and are called CD8+ T cells
upon activation, CD4 T cells differentiate …
to become T helper effector cells!
upon activation, CD8 T cells differentiate …
to become cytotoxic T cells
What is MHC? what chromosome encodes them?
MHC - Major Histocompatability Complex
Cell surface proteins encoded by a cluster of genes on human chromosome 6
structurally, MHC class I and II are similar, they both have this groove, peptide binding cleft which binds and presents peptide at the cell surface.
What determines which peptides can MHC molecule present?
The amino acids in MHC that contact the peptides determine precisely which peptides an MHC molecule can present.
What is the major barrier against transplantation?
MHC -
MHC is highly polymorphic.
Many different alleles
different alleles display different peptide repertoires.
what does it mean when MHC is polygenic, how many genes are there?
chromosome 6 there are actually three different class I genes in an Class I MHC locus. In humans this is called HLA. There are three major Class I genes. (similar with class II) so we have 3 versions of MHC class I and 3 versions of MHC class II. (and its more complicated because MHC is expressed co-dominantly)
what are the HLA, for MHC class I and MHC class II.
Within the MHC (called HLA in humans) there are:
- 3 Major class I genes: (HLA-A, HLA-B and HLA-C)
- 3 Major Class II genes: (HLA-DP, HLA-DQ, HLA-DR)
Where do we get this MHC diversity from?
- co expression of paternal and maternal alleles of each of our MHC genes (6 of them)
- we get a copy from mum and dad.
- so we each express 12 major MHC genes.
Antigen processing: MHC I pathway
MHC I tends to display intracellular (endogenous) peptides (CD8+ve T cells are recognising these peptides)
- cellular proteins are degraded in the cytoplasm by the proteasome
- peptides are pumped into the endoplasmic reticulum where they bind to class I MHC
- Class I MHC/peptide
Antigen processing: MHC II pathway
- extracellular proteins is endocytosed/phagocytosed
- proteins are degraded by the lysosome
- peptides are loaded onto Class II in SPECIALISED VESICLES
- MHC II /peptide is exported to the cell surface
What are the Three types of professional APC ? and whats different about them? (Hint: Micheal Phelps)
3 Types of professional Antigen presenting cells
Dendritic Cell, Macrophage, B lymphocyte
Macrophages and B lymphocytes are good at expanding and existing an immune response, very good secondary response.
However, dendritic cells have a unique property, only the dendritic cell can stimulate the Naive T cell. - it is only the dendritic cell that can initiate a primary immune response.
What are the two different functional/maturation states of the DENDRITIC CELL ? state some features
the IMMATURE (quiescent) stage. [ANTIGEN ACQUISITION] - induce T cell tolerance. immature dendritic cell, - highly phagocytic, - low MHC II (low antigen presentation) - low co-stimulation
BUT THEN, upon the receipt of PATTERN RECOGNITION with PAMPS, the dendritic cell changes morphology, shuts down its endocytic pathways and upregulates MHC class II & co-stimulatory molecules, and now becomes superbly adapted to present antigen to T cells to induce T cell immunity.
the ACTIVATED/MATURE stage [ANTIGEN PRESENTATION] :)
- low phagocytosis
-high MHC class II (high Antigen presentation)
- High co-stimulation
thus induce T cell immunity
By which cell and where in the body is the adaptive immune response initiated?
The adaptive immune responses are initiated by dendritic cells in the secondary lymphoid organs.
