Despite the importance of murine major histocompatibility complex (MHC
) class II I-A molecules for immunological rsearch, the overall peptid
e-binding specificities of I-A and the homologous human HLA-DQ molecul
es remain unresolved. Here, Boris Reizis and colleagues review current
evidence suggesting that DQ/IA molecules bind peptides with a differe
nt hierarchy of anchor positions than has been found in the well-chara
cterized DR/I-E proteins.