[Partial deletion of the D antigen in a family group. Determination of its antigenic density by flow cytometry].

UNLABELLED: Mutations within the genetic Rh system can produce partial deletions of one or more epitope of the D antigen, known as incomplete D. These people, classified Rh positive, are capable of producing anti-D antibodies when exposed to D positive red blood cells (rbcs). We describe the study of a Rh positive, 34 year old, spanish-indian ("mestiza") female patient, in whose blood anti-D antibodies were detected after a blood transfusions. The results of the tests showed a partial deletion of the D antigen in the patient and three of her family members.

PATIENTS AND

METHODS

The following tests were done to the patient and her family members: 1) ABO and Rh typing; 2) Direct antiglobulin test; 3) Detection of irregular antibodies in their blood serum; 4) Rh genotype; 5) Cross matching of the patient's serum with rbcs of her Rh positive relatives; 6) Titration of a monoclonal anti-D (IgM) and a polyclonal anti-D (IgG) of human origin with the patient's rbcs and with Rh positive rbcs of her family members whose erythrocytes didn't react with the patient's serum; 7) Measurement of the antigenic density of the D antigen by flow cytometry (indirect immunofluorescence) in the rbcs of the patient and in those family members who had the defect, using a polyclonal anti-D (IgG).

RESULTS

1) An anti-D antibody which didn't react with its own Rh positive rbcs was found in the patient's serum; 2) This antibody didn't react with the Rh positive rbcs of her father and two out of her 4 brothers; 3) The cytometric study of these cells (R)r) showed a immunofluorescence pattern weaker than the control cells of the same genotype, but with a variable expression between 15 to 41%.

CONCLUSIONS

The study showed: 1) The presence of an anti-D antibody in a Rh positive patient who had been previously sensitized (by blood transfusion); 2) This antibody was able to react with Rh positive rbcs but not with those of the patient and her family members who had the same partial deletion; 3) The defect was transmitted heterozygously, with a high degree of penetration, but with variable expression; 4) A low antigenic density for her D antigen by flow cytometry.