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Immunology - Lecture Thirty Three : Innate immunology III

Q: What are the roles of the different types of MHC ?

MHC-I Presents endogenous (intracellular) antigen and is expressed on all nucleated cells in the human body. Basically any cell with a nucleus, will have MHC-I This is because viruses like to grow inside cells and are the predominant pathogen presented on MHC-I MHC-II Presents exogenous (extracellular) antigen and is only an antigen presenting cell, making it a special cell Dendritic cells have both types of MHC present

6 important questions on Immunology - Lecture Thirty Three : Innate immunology III

What is the purpose of antigen uptake and Adaptive Immunity ?

Clearance of pathogens (innate response)
For presentation to T Cells (adaptive response)

ADAPTIVE IMMUNITY

Has evolved over time and are present in vertebrates (which need a complex immune system) but absent in invertebrates (who have innate immunity only)

Linking the Innate and Adaptive Immune Systems

The innate and adaptive immune systems are usually linked by antigen-presenting cells (dendritic cells and macrophages – dendritic cells are the most potent APC). These cells take samples of antigen and ‘present’ them to T cells via complexes on their cell surfaces. Presentation to T cells activates the adaptive immune system.

What is a Major Histocompatibility Complex (MHC) ?How are peptide-antigen presented on the MHC ?

It is present on antigen presenting cells, so that the cells are able to present peptides from pathogenic antigens to B-Cells or T-Cells

Dendritic Cells are one of the main types of Antigen Presenting Cells (APCs) and their function is to present peptides on MHC to T-Cells
Because it activates the T-Cells, MHC is essential for initiating adaptive immunity

What are the roles of the different types of MHC ?

MHC-I

Presents endogenous (intracellular) antigen and is expressed on all nucleated cells in the human body. Basically any cell with a nucleus, will have MHC-I
This is because viruses like to grow inside cells and are the predominant pathogen presented on MHC-I

MHC-II

Presents exogenous (extracellular) antigen and is only an antigen presenting cell, making it a special cell
Dendritic cells have both types of MHC present

How does MHC-I present endogenous antigens ?

Viruses invade different cells in the body and so their antigen will be present inside of the cell cytoplasm
Because we can't phagocytose the virus, theres no destruction of viruses in a phagolysosome
Instead the loading of the peptides onto MHC-I occurs in the endoplasmic reticulum of the cell and then the complex travels to the cell surface.
The destruction of the virus occurs in the cytoplasm

How are exogenous antigens loaded onto MHC-II?

Phagocytosis of the antigen occurs and is broken down into component parts by the phagolysosome which is acidic
The peptides from the antigen are loaded onto the MHC-II in the phagolysosome and sent to the cell surface. This displays the peptide for our B-Cells and T-Cells to detect