HLA-DQ3 (DQ3) is a broad serotype category with split antigens HLA-DQ7, DQ8, and DQ9.
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DQB1*0304 is similar in structure and function to DQB1*0301 generally considered to be HLA-DQ7
DQ7 is a form of 'split antigen' of the broad antigen group DQ3 which also contains DQ8 and DQ9.
The recognition of DQB1*0303 by DQ9 and or DQ3 is poorest, DQ2 which recognizes a different DQB1 subgroup recognizes DQB1*0303 as efficiently as DQ3.