Heidi, a few months ago I spent two hours on the phone with an enzymologist
from Land O Lakes talking about whether and what kind of cheeses are kosher,
etc. In the process I mentioned my history and he told me that different
cheeses have different protein chains or something like that and it is very
possible to be sensitive to one particular chain and not another. I haven't
been courageous enough to try him out on it. But one other thing was learned
about process cheese. It may have pork products to enhance the flavor, and
other ingredients. If your grilled cheese was made of process cheese, and
your pizza was made with real cheese, that may have made a difference. Or it
may have been the protein chain difference. Just a thought. cm