A2 Biology: Immune response help? Watch

ZettaLost
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I'm confused about what exactly happens when a normal body cell (not WBC) gets infected by a pathogen.

So basically the antigens from the pathogen will be presented on the cell membranes of the infected cell. How will the antigens be separated from the pathogens themselves? With WBCs like macrophages the pathogens are digested by enzymes in the lysozome and the antigens are separated. But with normal body cells the pathogens don't die do they ?

Next when the infected cell becomes an APC the T killer cells will bind to the MHC/antigen complex and, with the help of cytokines from T helper cells, they will divide to form clones of activated T killer cells and T killer memory cells. But what stimulates the T helper cells to release cytokines?

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Rob da Mop
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I spent all of my third year of undergrad doing immunology and virology and I don't fully understand the answers to these questions, but in simple terms:

There are a couple of ways to do the first thing. The fairly elegant way is for proteins, as they are being produced in the cell, to be broken down and presented on MHC straight away. This means that viruses, which must use host cell machinery for protein production, end up presenting viral peptides as soon as they start replicating. If you want to know more about this it's related to the DRiP hypothesis. Other ways are hazy and less well characterised. There are hints that cytosolic proteins are presented on MHC1 through various methods, but nothing concrete. It's important to remember that infected cells often die and then have their contents phagocytosed by surrounding APCs, which can then present the peptides.

A few things will stimulate T helper cells - most importantly binding to MHC-peptide on professional APCs themselves. Once activated by that they can be further activated by a number of things - conserved pathogenic structures known as PAMPs, other cytokines (confusingly) etc. When your body's infected the site of infection's a complete mess of immune cells, cytokines, cell debris and all sorts of rubbish that's far too difficult to go into in a few biology lessons or a TSR post, but that sort of thing stimulates T cells to release cytokines.
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