Introduction
We have already heard that there are two different kinds of MHC but in actual fact there are more! All MHCs originate from a large region of 4 million base-pairs on chromosome 6 that also codes for other proteins involved in antigen processing and presentation. There are three classes of genes: MHC class I, MHC class II and MHC class III. From here on we will only talk about MHC class II. But before we dive into more details about MHC class II presentation, we'd like to take a few moments to introduce two important concepts, MHC class II diversity and specificity. So hold on to your hats! We're going in for a little genetics trip!