The HLA-A and B supertype variation in worldwide populations was investigated in a recently published study by Francisco et al. (2015). Some functional differences between HLA-A and HLA-B were uncovered.

To learn more about these results : http://link.springer.com/article/10.1007/s00251-015-0875-9

Reference:
HLA supertype variation across populations: new insights into the role of natural selection in the evolution of HLA-A and HLA-B polymorphisms
Rodrigo dos Santos Francisco , Stéphane Buhler, José Manuel Nunes, Bárbara Domingues Bitarello, Gustavo Starvaggi França, Diogo Meyer, Alicia Sanchez-Mazas
Immunogenetics.