T-cells recognize the MHC molecules and body's own peptides. When it doesn't, it alarms the immune system. But do T-cells express MHC molecules ? If so, how are they using it? If not, what happens when a virus infects T-cells? (Yes, I am confused about HIV infection mechanism too. They escape from immune response by altering their genes and disrupting the MHC-peptide bonding. I can see that this can work in macrophages. But what is the situation in T-cells ?)
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$\begingroup$ They express MHC1. $\endgroup$– inf3rnoDec 13, 2014 at 19:33
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$\begingroup$ They do not express MHC II molecules. $\endgroup$– abcOct 28, 2016 at 6:00
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$\begingroup$ It is incorrect to say that T-cells do not express MHC class II molecules. Please see: ncbi.nlm.nih.gov/pubmed/15120183 $\endgroup$– Joel LeeFeb 12, 2017 at 0:56
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1 Answer
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There are two types of MHC molecules:
All nucleated cells express MHC class 1 proteins. A sample of all proteins produced within the cell are 'sliced' into their constituents which are then presented by MHC-I receptors. This means that if a virus infects a cell, the foreign proteins the cell is induced to make are expressed on the cell membrane by MHC-I. This is important as antibodies can not cross cell membranes, therefore this is the method by which a cell signals that it is infected by a virus.
MHC II are the special molecules that are only expressed in antigen-presenting cells, which I think is what you are referring to. As neither CD4 or CD8 T-cells present antigens, they do not express MHC-II themselves. Instead CD4 have receptors for MHCII (while CD8 have receptors for MHCI), allowing them to interact with antigens presented by other immune cells.
If a virus infects T-cells, the viral proteins are sampled by the MHC-I pathway and presented via MHC-I on the surface of the infected T-Cell. The immune response then progresses as for any other virally infected cell, destruction by CD8 T-Killers that destroy the cell by non-phagocytic means.
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$\begingroup$ Are you positive CD4 cells don't present antigens? I could have sworn they had the capability to. $\endgroup$– MCMDec 31, 2012 at 22:14
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$\begingroup$ @MCM that was off the top of my head, I'll have a read of my notes tomorrow. Happy New Year! $\endgroup$– Rory MDec 31, 2012 at 22:20
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$\begingroup$ Are antigen-presenting cells a specific type of cells? I've always been confused about this because the label seems so general. $\endgroup$– shigetaJan 1, 2013 at 15:37
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1$\begingroup$ @shigeta I would say they're a class of cell, defined by their expression of MHC-II. $\endgroup$– Rory MJan 1, 2013 at 22:49
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$\begingroup$ I would expect that they do something else besides only presenting antigen - is that their only function? $\endgroup$– shigetaJan 1, 2013 at 23:15