Antigen presentation, B cell responses
6 important questions on Antigen presentation, B cell responses
How are antigens prestentaed on MHC II?
- Antigen is taken up from extracellulaire space into endocytic vesicles
- In early endosomes of neutral PH, endosomal proteases are inactive
- protease are cathepsins
- by action of V-type ATPase, H+ ions are delivered into early endosome
- acidification of vesicles by fusion of lysosomes and endosome activates proteases to degrade antigen into peptide fragments
- vesicles with peptides fuse with vesicles with MCH II
How is premature binding pf peptides to newly MHC prevent?
- MHC is at ER membrane
- Invariant chain binds in the groove of MHC II
- Li is cleaved to leave a fragment bound to class II an to the membrane
- further cleavage leaves short peptide, CLIP, bound to MHC molecule
What the role of Li?
2. To target delivery of MHC II to low ph endosomal compartments
- Li forms a complex with MHC II, blocking binding of betides and misfolded proteins
- li is cleaved, leaving CLIP
- endocytosed antigens are degraded to peptides in endosomes, but CLIP prevent binding
- HLA-DM binds to MHC, releasing and allowing other peptides to bind
- HLA-DO binds to HLA-DM for negative regulator. So HLA-DM can dissociate with MCH
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What the role of BCR?
- Initiates a signaling cascade
- can deliver antigen to intracellulaire site, and are then returned to surface
Explain two antigens and their signals
- to recieven help from Tfh, B cells must present antigen for the T cell to recognize
- first signal is when antigen is bound to BCR, for B cell activation
- MHC-TCR
- Which lead to signals like CD40 on B cell and secretion of IL-21
- CD40 can activate canonical NFkB and non-canonical NFkB and enhance Mcl-1 (anti-apoptotic)
- IL-21 enhance proliferation and differentiation
Thymus independent antigen = antigens that are able to induce antibody production
- BCR bindt to antigen and TLR
How can intracellulaire bacterial evade the immune system?
- blocking phagosome-lysosome fusion
- escape from phagosome; into cytosol
- resistance to killing mechanism within the phagolysosome
Peptides can still be presentated and recognize by NK and t cellen
- leads to secretion of IFN-y and expression cd40L
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