Adaptive immune response ; recognition phase Flashcards
Can T cells be activated with the presentation of just a pathogen ?
NO , the only way T cells are activated is through an antigen presenting cell.
Give examples of antigen presenting cells ?
- macrophages
- monocytes
- dendritic cells
- langerhans cells
- B lymphocytes
What are extracellular pathogens ?
Bacteria , fungi , protozoa
What are intracellular pathogens ?
Viruses
What is a naive T cell ?
T cells that have not previously encountered the antigen
What are effector T cells
T cells that have previously encountered the antigen and are capable of performing effector functions during an immune response
What are MHC’s ? ( major histocompatibility complex) ?
They are found on the surface of cells.
What are the two main classes of MHC’s?
MHC class 1
MHC class 2
What are MHC class 1 molecules ?
These molecules are expressed on all nucleated cells , including antigen presenting cells that have MHC class 11 molecules expressed on them. Just not red blood cells.
- they bind to T lymphocytes ( eg cytoxic T cells) via CD8+ receptors.
- only intracellular microbes ( viruses) are presented via MHC class 1 molecules.
What are MHC class 11 molecules ?
Molecules that are ONLY found on antigen presenting cells.
- this is a MHC class that is used to present extracellular microbe antigens.
- antigen presenting cells are the only cells which carry out phagocytosis to obtain the antigens from extracellular microbes., so they must be the only cells with MHC class 11 proteins.
- they bind to CD4+ receptors on naive T cells.
What is another term for MHC molecules ?
HLA molecules
What are key features of MHC class 1 and class 11 molecules - rhat they both have in common ?
1) both have co-dominant expression : both MHC class 1 and class 11 parental molecules are co expressed in each individual.
2) POLYMORPHIC GENES : different individuals present and respond to different microbes
3) antigen presenting cells present intracellular microbes via MHC class 1 molecules ( HLA-A,B,C). Antigen presenting cells present extracellular microbes via MHC class 11 molecules( HLA-DP,DQ,DR)
Outline the process of fighting off intracellular microbes using MHC class 1.
1) As viruses enter any cells , MHC class 1 molecules are expressed on all cells. The virus enters the host cell cytosol.
2) the viral protein is marked for destruction by the proteasome.
3) proteasome breaks proteins into small antigenic peptide fragments.
4) If you have the right MHC class 1 molecules , then a complex is formed between the peptide + MHC molecule. This migrates out of the cell.
5) Antigen presenting cell presents the peptide-MHC complex to CD8 + T cells which leads to the activation of cytotoxic T cells. This killer cell then kills any infected body cells.
Outline the process of fighting off extracellular microbes using the exogenous pathway - MHC class 11 molecules
1) microbes are captured by phagocytosis or micropinocytosis
2) small fragments of the microbe binds to MHC class 11 molecules forming the peptide MHC class 11 complex if it is the right match.
3) the antigen presenting cells then present this peptide-MHC class 11 complex to CD4+ T cells. IL- is released and IL-2 receptors on the surface of the CD4+ lymphocyte surface are activated by the IL-2 as well as mononuclear phagocytes , increasing their microbicidal activity.
4) IL-2 also stimulates B cells to synthesise antibody.
Are MHC molecules very specific or have a very broad specificity?
They have a very broad specificity meaning they can present many different peptides by the same MHC molecule.
