Question

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?

Answer 1

Cytotoxic T cells recognize and kill infected cells by recognizing specific pathogen epitopes presented on the cell surface using MHC I molecules. Once an infected cell is recognized, the cytotoxic T cell releases perforin and granzymes, resulting in the apoptosis and destruction of the infected cell.

Step-by-step explanation:

Once activated, cytotoxic T cells recognize and kill cells infected with intracellular pathogens through the recognition of specific pathogen epitopes presented on the cell surface using MHC I molecules. This recognition is mediated by the T-cell receptor (TCR) on the cytotoxic T cell. When an infected cell presents the pathogen antigen on its MHC I molecules, the TCR of the cytotoxic T cell binds to the epitope and activates the cytotoxic T cell to release perforin and granzymes.

Perforin creates pores in the target cell, while granzymes enter the pores and induce apoptosis, resulting in the destruction of the infected cell without releasing the pathogens inside.