Serologic and biochemical studies of a previously unclassified blood type B variant.

The designation B4 is proposed for a weak variant of type B blood found in a Salvadorian woman and her two daughters. The red cells were weakly agglutinated by anti-B and anti-A,B; the serum contained anti-B; and the saliva contained H but not B substance. Biochemical studies of the serum showed that the enzyme specified by the variant B gene had low activity and low affinity for both sugar donor and acceptor.