Помогите, пожалуйста, разобраться с split antigen of the broad antigen

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The HLA Antigen Values and Split Equivalences table was created to resolve apparent differences in HLA
typing results which occur between laboratories that should be considered equivalent. Generally these
differences occur at the level of HLA antigen splits – two or more closely structured HLA antigens which
together comprise a parent antigen. For example, HLA-A28 (parent antigen) has been “split” to yield two
related antigens (splits): HLA-A68 and HLA-A69.