FIRST REPORT OF AN ANTI-D AUTOANTIBODY IN A PATIENT WITH A DEL PHENOTYPE

MUFARREGE, NICOLÁS; PRINCIPI, CINTIA; TRUCCO BOGGIONE, CAROLINA; LUJÁN BRAJOVICH, MELINA ELIANA; MATTALONI, STELLA MARIS; ENSINCK, MARÍA ALEJANDRA; BIONDI, CLAUDIA; COTORRUELO, CARLOS

Congreso; 36th International ISBT Congress; 2020

FIRST REPORT OF AN ANTI-D AUTOANTIBODY IN A PATIENT WITH A DEL PHENOTYPENicolás Mufarrege, Cintia Príncipi, Carolina Trucco Boggione, Melina Luján Brajovich, Stella Mattaloni, Alejandra Ensinck, Claudia Biondi, Carlos CotorrueloLaboratorio de Inmunohematología. IDICER – CONICET. Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario. Rosario, Argentina.The D antigen is the most immunogenic of the Rh blood group system and therefore the most important clinically regarding transfusion- and pregnancy-induced immunization. A plethora of allelic variants of D exists. DEL is the weakest form of D, which makes such phenotype appear D negative even when anti-D typing is performed with a sensitive indirect antiglobulin test (IAT). DEL can only be detected serologically by adsorption – elution assays. Almost 50 RHD alleles are responsible for DEL phenotypes and in a previous study performed in our country we have reported a relatively high prevalence of the rare RHD*DEL43 allele. It is has been published that some individuals harboring DEL phenotypes developed anti-D alloantibodies after transfusion or pregnancy. However, DEL individuals with an anti-D autoantibody are still unreported.aIM:To elucidate the allele harbored by a patient with a D typing discrepancy and an anti-D autoantibody.Methods: A blood sample from a 57-year-old man, who was initially typed as extremely weak D and after three months of one D positive unit transfusion, an anti-D antibody was detected together with positive direct antiglobulin test (DAT), was referred to our laboratory for further investigation. Rh phenotype, antibody screening and identification as well as DAT were performed by standard tube and gel matrix techniques. Additionally, elution tests were done using an acid-elution-based kit. Genomic DNA was isolated with a silica-membrane-based purification kit. RHD-specific regions and RHCE, RHD*weak D type 2 and RHD*DEL43 alleles were investigated by PCR strategies.Results: The proband was found to be D negative even in IAT. Standard serotyping demonstrated a C-, c+, E+, e+ phenotype. The DAT was markedly positive with an anti-IgG serum and negative with an anti-C3d reagent. An antibody with anti-D specificity was identified both in plasma and in red blood cells eluate. Anti-LW specificity was ruled out because dithiothreitol treatment of panel cells did not attenuate positive reactions. RHCE genotyping was found to be in concordance with the RhCE phenotype. RHD gene fragments and the RHD*DEL43 allele were detected in the proposita, revealing a DEL phenotype.Summary/Conclusions: These findings indicated that the patient harbored the RHD*DEL43 allele which is characterized by the c.46T>C missense mutation that caused the p.Trp16Arg amino acid substitution predicted to be in the first transmembrane segment of the RhD protein. He was found to be sensitized to the D antigen, apparently because of the D positive unit transfused three months before. In previous studies, we have noticed that the D antigen density produced by the RHD*DEL43 allele is borderline between weak D and DEL because a very weak reaction in saline with some IgM anti-D clones is sometime observed. This behavior may be responsible for the weak D phenotype initially detected in the patient and the D negative phenotype observed in our study. The anti-D identified was an autoantibody as showed by the positive DAT. To note, the RHD*DEL43 allele has been found in approximately 5% of the D negative C/E positive donors of our country. So far, no reports were available describing DEL patients who have developed an anti-D autoantibody. Finally, the accurate allele identification responsible for a variant phenotype would definitely contribute to transfusion safety.