A review of the Chido/Rodgers blood group.

The C4 protein plays an important role in maintaining health and, in some situations complicated by poor expression of the C4 protein, may lead to or exacerbate certain diseases. The blood groups Chido and Rodgers are epitopes on the C4 protein, and polymorphisms associated with these epitopes may lead to the formation of antibodies to the Chido or Rodgers antigens in transfused patients. Identification of anti-Ch or anti-Rg is still based on the antibody neutralization with plasma from Ch-positive or Rg-positive individuals and lack of reactivity with qualified Ch-negative or Rg-negative RBCs. These antibodies may be useful in genetic studies of C4 polymorphisms or, in the case of C4-deficient patients, a signal of the potential for serious illnesses. The recognition of the extreme polymorphism of the C4 gene and the gene complex RCCX should lead to more insights in the understanding of disease risk and potential treatment.