Two MER2-negative individuals with the same novel CD151 mutation and evidence for clinical significance of anti-MER2.

BACKGROUND: MER2 (RAPH1), the only antigen of the RAPH blood group system, is located on the tetraspanin CD151. Only four examples of alloanti-MER2 are known. We report here two new examples of alloanti-MER2, in women of Pakistani and Turkish origin, one of whom showed signs of a hemolytic transfusion reaction (HTR) after transfusion of 3 units of red cells (RBCs). STUDY DESIGN AND METHODS: Standard serologic methods were used. A monocyte monolayer assay (MMA) was used to assess the potential clinical significance of one of the antibodies. All exons and flanking intronic sequences of CD151 were amplified and sequenced. A homology model for CD151 second extracellular loop (EC2) was constructed based on the crystal structure of CD81. RESULTS: RBCs of both patients did not react with alloanti-MER2, and neither of their antibodies reacted with MER2-negative RBCs. The MMA results suggested that the antibody that appeared to have caused an HTR had the potential to be clinically significant. Both patients were homozygous for a 511C>T mutation in CD151 encoding an Arg171Cys change. This change did not result in any significant structural rearrangement in the protein model. CONCLUSIONS: Two MER2-negative patients with anti-MER2 are homozygous for the same novel mutation encoding an amino acid substitution in the EC2 of CD151. One of the antibodies may have been responsible for an HTR, and crossmatch-compatible RBCs should be recommended for transfusion to patients with anti-MER2.

Two missense mutations in the CD44 gene encode two new antigens of the Indian blood group system.

BACKGROUND: Blood samples were referred over a 10-year period from five patients whose serum samples contained antibodies to unidentified high-incidence antigens. Three patients (A, B, C) were of Moroccan origin and their antibodies and red blood cells (RBCs) were mutually compatible, but incompatible with those of the other two patients (D, E), who were of Pakistani origin. The antibodies and RBCs of D and E were mutually compatible, but incompatible with those of Patients A, B, and C. All the antibodies were detected during pregnancy. STUDY DESIGN AND METHODS: Serologic tests, including the use of enzyme-treated and chemically modified RBCs, suggested a relationship to CD44 (Indian blood group system). The monoclonal antibody immobilization of erythrocyte antigens (MAIEA) assay with monoclonal CD44 antibodies, immunoblotting of RBC membranes, and CD44 gene sequencing were carried out. RESULTS: Positive reactions in the MAIEA assay confirmed that the patients' antibodies are directed at CD44. Immunoblotting with two of the antibodies gave positive reactions of identical size to monoclonal anti-CD44 and failed to react with the RBCs of a CD44-deficient patient. One of the antibodies reacted with purified CD44. Sequencing of Exons 1 to 5 of CD44 revealed 255C>G in Exon 3 for A, B, and C encoding H85Q and 488C>A in Exon 5 for D and E encoding T163K [corrected] CONCLUSION: Two novel CD44 antigens of high incidence have been identified: IN3 (INFI) and IN4 (INJA) in the IN (Indian) blood group system. Lack of IN3 and IN4 results from homozygosity for mutations encoding H85Q and T163R in CD44, respectively.

A KEL gene encoding serine at position 193 of the Kell glycoprotein results in expression of KEL1 antigen.

BACKGROUND: The KEL2/KEL1 (k/K) blood group polymorphism represents 578C>T in the KEL gene and Thr193Met in the Kell glycoprotein. Anti-KEL1 can cause severe hemolytic disease of the fetus and newborn. Molecular genotyping for KEL*1 is routinely used for assessing whether a fetus is at risk. Red blood cells (RBCs) from a KEL:1 blood donor (D1) were found to have abnormal KEL1 expression during evaluation of anti-KEL1 reagents. STUDY DESIGN AND METHODS: Kell genotyping methods, including KEL exon 6 direct sequencing, were applied. KEL cDNA from D1 was sequenced. Flow cytometry was used to assess KEL1 and KEL2 RBC expression. RESULTS: RBCs from the donor, her mother, and an unrelated donor gave weak or negative reactions with some anti-KEL1 reagents. Other Kell-system antigens appeared normal. The three individuals were homozygous for KEL C578 (KEL*2) but heterozygous for a 577A>T transversion, encoding Ser193. They appeared to be KEL*2 homozygotes by routine genotyping methods. Flow cytometry revealed weak KEL1 expression and normal KEL2, similar to that of KEL*2 homozygotes. CONCLUSION: Ser193 in the Kell glycoprotein appears to result in expression of abnormal KEL1, in addition to KEL2. The mutation is not detected by routine Kell genotyping methods and, because of unpredicted KEL1 expression, could lead to a misdiagnosis.