Conceptual framework shifts in immunogenetics. I. A new look at cis AB antigens in the ABO system.

The so-called 'cis AB' blood group is accounted for by proposing that 'normal' anti-A and anti-B reagents are cross-reacting with partially overlapping reaction ranges. Hence, they are labelled anti-AX and anti-BX, respectively. Some consequences of a complex-simple model where 'cis AB' is accordingly produced by a simple (mono-factorial) antigen X (produced a simple gene X at the ABO-locus) are briefly explored.