Grades 9–12 · Organisms
Why can ABO antibodies react with some red blood cells?
Red blood cells have many surface markers called antigens. The ABO system describes whether A markers, B markers, both or neither are present. Group A cells have A markers, group B cells have B markers, group AB cells have both, and group O cells have neither A nor B. Group O cells still carry many other kinds of markers.
In the diagramABO antibodies can recognize red-cell antigensRed cells from one group · plasma antibodies of another groupRed cells: group ARecipient: group BAA/B surface markersanti-AAntibodies in plasmaMatching antibody can bind the red-cell marker.ABO red cells only · Rh and other compatibility factors omitted
Antibodies are in the plasma, the liquid surrounding blood cells. In the usual ABO pattern, group A plasma contains anti-B, group B contains anti-A, group O contains both, and group AB contains neither. These names describe what the antibodies recognize. Anti-A can bind A markers; anti-B can bind B markers.
When a recipient’s plasma contains an antibody matching a marker on introduced red cells, binding can trigger damaging immune reactions. For example, anti-A in group B plasma can recognize group A red cells. The comparison therefore follows two different components: markers on the introduced cells and antibodies in the recipient’s plasma.
A comparison about red cells cannot simply be reused for plasma. Introduced plasma brings its own antibodies, so the direction of the question changes. ABO is also only one part of compatibility: Rh antigens and many other factors matter. The diagram reports only whether this limited A/B antibody conflict exists, and cannot establish clinical compatibility or donation suitability.
About this explanation
Starting knowledge: Understand antigens, antibodies and the difference between blood cells and plasma.
Sources
- NHS — Blood groups
- NHS Blood and Transplant — Blood types