Rh blood group G antigen (RhG)

The Rh blood group G antigen (RhG), designated as Rh4 in the ISBT nomenclature, is a clinically significant erythrocyte surface antigen within the Rhesus (Rh) blood group system. It is an epitope located on both the RhD protein and the RhCe protein, specifically associated with the presence of a Serine residue at amino acid position 103 (Ser103). The G antigen is found on the red blood cells of individuals who possess either the D or C antigens; conversely, it is absent in individuals with the 'rr' (dce/dce) phenotype who lack both D and C. In clinical practice, the G antigen is primarily relevant in the fields of transfusion medicine and obstetrics due to its role in alloimmunization. Antibodies against the G antigen (anti-G) can cause hemolytic disease of the fetus and newborn (HDFN) and hemolytic transfusion reactions. Because anti-G often mimics the appearance of combined anti-D and anti-C in serological assays, specialized monoclonal antibodies like the 3SM2 clone are used to distinguish true anti-G sensitization. This distinction is critical for prenatal care, as women sensitized only to the G antigen remain candidates for Rho(D) immune globulin prophylaxis if the fetus is RhD-positive.

Other names

Rh4G epitopeRhesus G antigenRh blood group G protein

Antibody-mediated immune suppression (AMIS) to prevent maternal alloimmunization; passive immunization for the prevention of hemolytic disease.