00:01 So those are the two classically defined processes of antigen presentation. 00:08 The presentation of endogenous antigen to CD8+ T-cells using MHC Class I, and the presentation of exogenous antigen to CD4+ T-cells using MHC Class II. 00:25 But in fact, those pathways are not absolutely set, they’re kind of interconnected in you like. 00:30 An exogenous antigen can be presented using MHC Class I. 00:35 An endogenous antigen presented using MHC Class II, as we can see on this particular slide. 00:41 And this isn’t a rare event. 00:43 This is happening all the time because often you will want exogenous antigens to be presented to CD8+ T-cells and you’ll want endogenous antigens to be presented to CD4+ helper and regulatory T-cells. 00:58 So the endogenous and exogenous pathways are not completely separated from each other. 01:04 Endogenous antigens can enter the Class II pathway and be presented to CD4+ helper and regulatory T-cells. 01:12 And exogenous antigens can enter the Class I pathway and be presented to CD8+ cytotoxic T-cells. 01:21 Let’s just look at one example of cross presentation. 01:25 Here we have a virus infected cell. 01:29 And antigens are being processed and presented using MHC Class I on this virus infected cell. 01:38 However, you can have capture of these antigens, either infected cells or viral antigens that are picked up by the antigen presenting cells in the infected individual. 01:51 So for example a dendritic cell can pick up antigen, and these viral antigens can then enter the cytosol. 02:00 So they’ve been engulfed by endocytosis or phagocytosis, and normally they would be given to the MHC Class II pathway. 02:09 But now they’re being put into the MHC Class I pathway because the antigen escapes from the vesicles and enters the cytosol. 02:17 And then they can go through the normal Class I pathway using that immunoproteasome that we heard about. 02:24 And you get this cross presentation so that MHC Class I is presenting, using a dendritic cell, MHC Class I is presenting to virus specific CD8+ T-cells. 02:38 And you get co-stimulation and activation of these cytotoxic T-cells.
The lecture Cross-Presentation – Antigen Processing and Presentation by Peter Delves, PhD is from the course Adaptive Immune System.
Which of the following best defines antigen cross-presentation?
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