The SdaBlood Group Antigen in Tissues and Body Fluids

Abstract. In man the Sd^aantigen is present in most secretions with the greatest concentration in urine. There is little difference in the amount of Sd^asubstance in the urine of newborn infants, pregnant women and normal adults but there is a much greater amount in the saliva of newborn infants than in adults. Approximately half the people whose red cells group as Sd(a-) secrete Sd^asubstance in the urine. Anti-Sd^aantibody is present in 50% of Sd(a-) non-secretors of Sd^asubstance, though most of these antibodies only react with the strongest Sd(a +) cells. The greatest Sd^aactivity has been found in human meconium, guinea pig urine and guinea pig kidney. Activity can be detected in the urine of many animal species. The kidneys of 5 bird species did not contain Sd^a.