ABO antigen levels on platelets of normal and variant ABO blood group individuals

ABO Incompatibility between the Mother and Fetus Does Not Protect against Anti-Human Platelet Antigen-1a Immunization by Pregnancy

(1) Background: ABO blood group incompatibility between the mother and fetus protects against anti-D immunization by pregnancy. The possible role of ABO incompatibility in protecting against anti-human platelet antigen-1a immunization is unclear. (2) Methods: This study retrospectively screened 817 families (mother-father-neonate trios) of suspected fetal and neonatal alloimmune thrombocytopenia for inclusion. ABO genotypes were determined in 118 mother-child pairs with confirmed alloimmune thrombocytopenia due to anti-HPA-1a antibodies, and 522 mother-child pairs served as the control group. The expression of blood group antigen A on platelets was determined in 199 consecutive newborns by flow cytometry and compared with adult controls. (3) Results: ABO incompatibility between mother and fetus did not protect against anti-human platelet antigen-1a immunization by pregnancy. ABO blood groups of mothers and/or fetuses were not associated with the severity of fetal and neonatal alloimmune thrombocytopenia. The expression pattern of blood group A antigens on the platelets of newborns mirrored that of adults, albeit on a lower level. Blood group A antigen was detected on a subpopulation of neonatal platelets, and some newborns revealed high platelet expression of A determinants on all platelets (type II high-expressers). (4) Conclusion: The lack of a protective effect of ABO incompatibility between mother and fetus against anti-human platelet antigen-1a immunization by pregnancy may indicate that fetal platelets are not the cellular source by which the mother is immunized.

Cord Platelet Count of Full-Term Neonates in Relation to ABO Incompatibility and Glucose-6-Phosphate Dehydrogenase Levels: A Retrospective Cohort Study

Background The immunoglobulin G of mothers with O blood type may sensitize the platelets of their neonates with A (O-A incompatibility) or B (O-B incompatibility) blood type. As the expression and antigenicity of the B antigen on platelets is less than that of the A antigens, we have hypothesized that platelet count is higher in the O-B incompatibility group compared to the O-A incompatibility group. There is controversy about whether glucose-6-phosphate dehydrogenase (G6PD) deficiency, without evidence of hemolysis, is associated with a lower platelet count than G6PD-normal. Aim To assess whether platelet count is higher in the O-B than in the O-A incompatible neonates and whether it correlates with their G6PD levels. Methods This study was a retrospective cohort study on a sample of 835 healthy neonates born at ≥38 weeks gestation who were either A or B blood types with mothers that carried the blood type O Rh-positive. The platelet count (thousand per microliter) from umbilical cord venous blood (UCVB) was used. A G6PD level of 11.0 units/gram of hemoglobin (U/g Hb) was considered the lower reference limit. G6PD deficiency was defined as a G6PD level of <3.3 U/g Hb in both sexes. Intermediate G6PD deficiency in females was described as a G6PD level of 3.3-8.8 U/g Hb. Results The mean UCVB platelet count was higher in female neonates compared to male neonates (n=389, 283±65 versus n=446, 272±73, p=0.01). The mean UCVB platelet count was higher in the O-B incompatibility group in both male (n=114, 291±82 versus n=103, 266±63) and female neonates (n=83, 303±66 versus n=81, 278±58) with G6PD levels of >8.8 U/g Hb. There was a positive weak correlation between UCVB platelet counts and G6PD levels only in O-B incompatible female neonates (n=176, r=0.23, p=0.002). The partitioning and combined 95% reference intervals (RIs) of the UCVB platelet count were presented. Conclusion The platelet count was higher in the O-B incompatibility group compared to the O-A incompatibility group, but only when the G6PD level was >8.8 U/g Hb. A correlation between UCVB platelet count and G6PD levels was found only among O-B incompatible female neonates. These findings may have an important implication in estimating RIs of the UCVB platelet count, however, they need to be confirmed and explored in future research.

Neonatal alloimmune thrombocytopenia due to anti-HPA 5a in a HPA-5a homozygous neonate

The most frequently involved antigen in severe fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the human platelet antigen 1a. Cases of FNAIT caused by HPA-5a antigen are extremely rare, and usually not severe. We report a case of FNAIT caused by anti-HPA antibodies directed to the HPA-5a antigen. The thrombocytopenia was moderate with a minimal platelet count of 36 × 10⁹/L by day 3, and spontaneously resolved by day 10. The pregnancy had been obtained by in vitro fertilization using embryo donation, creating a complete genetic disparity between the HPA 5b5b mother and the HPA 5a5a homozygous neonate. The use of ART with gamete donation can increase the risk and the severity of alloimmune thrombocytopenia and must be considered in new and subsequent pregnancies.

[Coagulation test features depending on the AB0-blood groups system antigenic composition.]

The maintenance of normal blood flow through the vessels is the result of the coordinated work of the coagulation and anticoagulation systems of our body. The balance of this system depends on many factors, including endothelial, humoral, platelet ones, however, we still lack knowledge about the effect of antigenic determinants on the state of the hemostatic system. This study is devoted to assessing the effect of the presence and absence of antigens on the AB0 system, presented on erythrocyte and platelet membranes, on hemostatic parameters. The study was conducted in the Clinics of Samara State Medical University and consisted of127 clinically healthy individuals who underwent a general analysis and biochemical blood analysis, 52 people with the most stable indicators of cell composition and metabolic profile were selected for a coagulation test, including determination of the activity of coagulation factors and routine tests. A significant decrease in the activity of the VIII and VII coagulation factors was revealed, as well as an increase in the prothrombin time in patients with 0 (I) blood group compared to the "antigenic" blood groups. The presence of biological variation for indicators of external and internal coagulation paths was noted, depending on the group of blood belonging to the AB0 system. The findings suggest that there is an increased susceptibility to bleeding in patients with 0 (I) blood groups due to the absence of antigenic determinants on the cell membrane, while for "antigenic" blood groups, on the contrary, there is a susceptibility to thrombosis due to increased activity of the components of the coagulation system.