Introduction Antigens must be presented to the adaptive immune system so that specialized antigen presenting cells (APCs) can activate the immune system killer T-cells can monitor the intracellular contents of all cells helper T-cells can be alerted to both intracellular and extracellular antigens Two types of antigens are processed by cells for presentation on the cell surface endogenous antigens are proteins produced by the cell exogenous antigens are proteins that are taken up by the cell Both types are linked to major histocompatability complexes (MHC) during processing so that they can be stably exported to the cell surface they can be recognized specifically by T-cells Antigens are presented to two distinct cell populations including CD4+ helper T-cells that recognize antigens loaded onto MHC class II CD8+ killer T-cells that recognize antigens loaded onto MHC class I Antigen Processing Antigens must undergo a number of transformations before being presented including degradation of proteins into component peptides translocation of the peptides into the appropriate compartment loading of the peptides onto MHC proteins The processing of antigens must therefore preserve information about the location from where the antigen originated the type of response that is required Antigen Processing Pathways Feature MHC Class I MHC Class II Function Allow for sampling of intracellular antigens Signal that a cell is infected or abnormal Allow for sampling of extracellular antigens Signal that pathogens are within the host Target cell CD8+ killer T-cells Rule of 8: (MHC) 1 x (CD) 8 = 8 CD4+ helper T-cells Rule of 8: (MHC) 2 x (CD) 4 = 8 Antigens Endogenous antigens Exogenous antigens Degradation By proteosomes in the cytosol By proteases in the phagosome Translocation Into ER by TAP proteins Into endosomes after phagocytosis Loading Directly bind to MHC I Bind to MHC II after release of invariant chain Defect Absent CD8+ activity Absent CD4+ activity Antigen Presentation After processing, antigenic peptides are loaded on surface MHC proteins where T-cell receptors can bind specifically to the peptide CD4 and CD8 can bind specifically to the corresponding MHC Integrins can bind APCs Together, this set of interactions allows for specific detection of antigens activation of T-cells References
QUESTIONS 1 of 2 1 2 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.IM.13.24) Antigen presentation of extracellular pathogens by antigen presenting cells requires endocytosis of the antigen, followed by the degradation in the acidic environment of the formed phagolysosome. Should the phagolysosome become unable to lower its pH, what is the most likely consequence? Tested Concept QID: 100445 Type & Select Correct Answer 1 Deficient NK cell activation 4% (2/51) 2 Deficient presentation of pathogens to CD4 T-cells 71% (36/51) 3 Deficient presentation of pathogens to CD8 T-cells 14% (7/51) 4 Deficient cell extravasation 8% (4/51) 5 Deficient expression of B7 2% (1/51) M 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review tested concept