The CD235ab (HIR2) antibody recognizes a N-terminal homologous portion of glycophorin-A (GPA) and glycophorin-B (GPB), which are single-pass membrane sialoglycoproteins. GPA is the carrier of blood group M and N specificities while GPB accounts for S, s and U specificities. GPA and GPB provide the cells with a large mucin-like surface acting as a barrier to cell fusion, therefore minimizing aggregation between red blood cells in the circulation. The CD235ab (HIR2) antibody agglutinates untreated RBC but failed to agglutinate papain-treated cells. This antibody primarly binds to GPA and weakly to GPB. CD235ab is expressed on early erythroblasts, late erythroblasts, erythroblasts, mature erythrocytes and the cells of erythroid cell lines K562 and HEL, but not on all other cells. Mature erythrocytes are CD235ab positive whereas CD45 and CD71 negative.