CONICET | Buscador de Institutos y Recursos Humanos

ABO anti-A and anti-B IgM antibodies are not detected in cord serum by hemagglutination methods. The appearance of these isohemagglutinins regularly and naturally in all healthy individuals after a one year of age has been attributed to the immaturity of B1 cells in the newborn. The aim of this study was to investigate the presence of anti-A IgM antibodies in O blood group neonates using flow cytometry. Serum samples obtained from umbilical cord of blood group O newborns (n = 25) were incubated with 0.2% red blood cell (RBC) suspensions from group O (negative control) and group A adult normal volunteer donors. After washing with phosphate-buffered saline (PBS), samples were labeled with anti-IgM conjugated to APC for 30 minutes at RT in the dark, washed with PBS and resuspended in sheat fluid. Samples were acquired on a FACSAria II cytometer. Two hundred thousand events were evaluated in duplicate for each sample and data were analyzed with the FACSDiva software. The RBC population was selected based on its characteristics of FSC (cell size) versus SSC (cell density). The percentage (%) values of RBCs with bound IgM for A RBCs and O RBCs, expressed as mean ± standard deviation were 0.72% ± 1.67% and 0.11% ± 0.04%, respectively. The results obtained showed a significant increase (p <0.005) in the percentage of RBCs with bound IgM when using A RBCs respect to O RBC (Wilcoxon test). From the analysis of the 25 paired samples arises that in 5 of them the difference between the % of A RBCs with bound IgM and O RBCs with bound IgM is greater than 0.4%. These findings show the presence of anti-A IgM antibodies in approximately 20% of the cord blood serum of newborns. Because there are no receptors to allow transplacental transport of IgM antibodies, the results suggest that the isohemagglutinins detected had been synthesized by the fetus.

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