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A dendritic cell engulfs an antigen and presents it on its membrane with MHC II. This then binds to an antibody on the membrane of a T cell. It activates the T cell, let's call this X. This X then becomes X1, helper T cell, and X2, cytotoxic T cell.

A B cell with its antibody on its membrane encounters the same antigen and engulfs it. It starts producing IgM (right?). It then presents this antigen with MHC II (or I?), let's call this B cell Y. To the helper T cell, X1, the activated B cell, Y, presents the antigen and MHC II complex to X1 and then the X1 releases cytokines to Y, which then starts producing IgG antibodies (right?).

Now my main question is, what happens to the cytotoxic T cell? It goes and kills the pathogens but how does it know which one is a pathogen? Are the pathogens recognised by simply that the cytotoxic T cell realises that the pathogen has a different MHC? So is the point of the MHCs so that the cytotoxic T cells do not kills their own cells? So do cytotoxic T cells also kill infected cells? But the infected cells have a own body MHC so how does the cytotoxic T cell kill it when it recognises it as the own bodies cell? In other words, how does it recognise it as infected? And why must infected cells be killed anyways? Why not just prevent the pathogen from spreading to other cells? Or I mean do normal healthy cells even present MHCs? Or only the viruses, bacterias, and the infected cells? Is then the dendritic cell also killed since it presents MHC?

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