In class a few days ago my professor was explaining how most cells in our body contain a marker which distinguishes them as being apart of our bodies rather than foreign and possibly dangerous. He said that this marker was the glycoprotein MHC I. He also said that RBC did not contain this marker, so, I was wonder why our bodies don't attack our red blood cells (RBC). ((I know this forum was for med students only, but my professor is a Doctor and can't explain this)) Please help!
I am obviously not a med student so do not take my answer as truth in anyway. Let's see how much I remember from Anatomy.
When T-cells encounter an APC, as you said, they check to see if its one of the bodies cells by and antigen on the MHC protein. T-cells respond to two types of MHC proteins.
MHC I proteins- occur in every nucleated cell of the body, except erythrocytes. These proteins are produced by the cells and placed on the plasma membrane. On the way to the plasma membrane they pick up peptides in the cytoplasm and display them once they are on the plasma membrane. The immune system recognizes the peptides as its own cells and does not attack.
MHC II proteins (HLA's)- Only occur on APCs and display foreign antigens.
Cytotoxic T-cells respond to MHC-I while Helper T-cells respond to MHC-II.
Since the erythrocytes do not present the MHC-I antigens on their surface, the
body does not attack them.
However, Anti-A & B antigens, packed RBC vs. Whole blood transfusions are a different senario. The body does not attack the blood cells but they begin to agglutinate.