Antigen Processing & Presentation Flashcards
Describe what antigen processing & presentation is.
APCs (macrophage, dendritic, B cells) digest antigen from outside/inside the cell & display the antigenic fragments on cell surface of MHC for recognition by T lymphocytes to initiate a immune response.
*without APC there would be no T cell response.
Describe the 3 professional APCs.
- Dendritic
-present antigen to naive CD4 & CD8 T lymphocyte - Macrophage
-present antigen to differentiated (effector) CD4 T lymphocytes cell mediated immunity - B lymphocytes
-present antigen to helper CD4 T lymphocytes humoral immune response
Describe non professional APCs.
all other nucleated cells that when they become infected with a virus can act as APCs (not main function)
Describe the distribution & properties of APCs.
Describe the 2 functions of APCs.
- Convert protein antigens to peptides within APCs = antigen processing
- APCs provide stimulus to T cells = co stimulation
Describe how antigen presentation begins with antigen processing.
-convert protein antigens from extracellular or cytosol into peptides & onto MHC to display to lymphocytes
>protein antigens in acidic vesicular areas of APCs = MHC class II associated peptides
>antigens in cytosol = MHC class I associated peptides
Describe the process of endocytosed antigens for MHC class II. (UPTAKE)
*uptake of extracellular protein into vesicular compartment of APC
>receptor mediated macrophages & dendritic cells on surface to bind microbes
>B lymphocytes use BCR to internalize antigen & localized in endosomes that have proteolytic enzymes that communicate w lysosomes to make phagolysosome to degrade engulfed material
Describe the process of endocytosed antigens for MHC class II. (PROCESSING)
*processing of internalized proteins in endosomal or lysosomal vesicles
-14-20aa peptides made that bind to peptide binding cleft of MHC II
*cathepsins are most imp proteolytic enzymes involved in degradation
Describe the process of endocytosed antigens for MHC class II. (BIOSYNTHESIS)
*biosynthesis & transport of MHC II to endosomes
-a & B chain of MHC II synthesized in ER & transport to GA & then to endosomes with an invariant chain (Ii)
Describe the process of endocytosed antigens for MHC class II. (ASSOCIATION)
*association of processed peptides with MHC II in endocytic vesicles
-in endosomes the invariant chain dissociates & the antigenic peptides are associated with MHC II
Describe the process of endocytosed antigens for MHC class II. (EXPRESSION)
*expression of peptide class II complex on APC surface
-displayed for recog by CD4 T lymphocytes
Describe the processing of cytosolic antigens for MHC class I. (CYTOSOL SOURCE + PROCESSING)
Source:
-proteins in cytosol endogenously synthesized in nucleated cells
-may originate from viruses or other intracellular microbes
-endocytosed antigens may be presented through MHC I
Processing:
-cytosolic proteins antigens are ubiquitinated -> proteosomal degradation (protein to peptide) ‘proteolysis in proteasome’
>proteasome = multi enzyme complex in cytoplasm
Describe the processing of cytosolic antigens for MHC class I. (TRANSPORT)
*transport of peptides from cytosol to ER via transporter associated w antigen presentation (TAP)
-TAP located in ER
Describe the processing of cytosolic antigens for MHC class I. (ASSEMBLY)
*assembly of peptide MHC I complex in ER
Describe the processing of cytosolic antigens for MHC class I. (SURFACE EXPRESSION)
*surface expression of peptide MHC I complex
-MHC I peptide complex move thru golgi complex & delivered to cell surface
-once expressed the complex may be recognized by peptide antigen specific CD 8 T lymphocytes