Synopsis: Certain cells of the immune system and
cells that are infected present small regions of antigens on
their surface in association with MHC molecules. Cells of
the immune system will detect the presented antigens and the
immune response is thus activated. This assay is a
competetive one in that a radioactively tagged peptide is
added to a solution along with the test peptide, both of
which can bind to the same molecule, the MHC in this case.
The more of the tagged peptide that binds, the greater its
affinity is for that molecule, and the less of the tagged
peptide that binds, the greater the affinity of the test
peptide for the binding molecule. These researchers studied
the binding activity of the epitope p11C with the MHC class
I molecule Mamu-A*01.
Why are MHC molecules like Mamu-A*01 so
important for the immune system's fight against viruses when
the body has other mechanisms like phagocytic cells and
antibodies?
What are some of the ways the virus can thwart this
safety mechanism?
Procedure:
1.
2x10^6 Cells expressing Mamu-A*01 were incubated with
iodinated (labeled) p11C peptide overnight at 26
C.
2.
The cells were washed and divided into sets, one of each
which was incubated with one of several dilutions of
unlabeled test peptides for 4 hours at 20 C.
3.
The radioactivity of the cell pellet was measured with a
scintillation counter and calculated as 1-(c.p.m. with
competitor peptide/c.p.m. without competitor peptide).
*(the test peptides is the competitor peptide)
What would the radioactivity of the pellet tell
us?