AbstractBackgroundBoth M and N alleles encode antigens on Glycophorin A (GPA), a red blood cell (RBC) surface sialoglycoprotein. Interaction between RBC GPA and leukocyte surface lectins may downregulate their activation. The current study investigates if RBC autoantibodies against GPA, such as auto‐anti‐M/N, prime an activated phenotype in peripheral blood leukocytes.MethodsLeukocyte activation was assessed in whole blood from patients with auto‐anti‐GPA (anti‐M/N) and compared to those with allo‐anti‐M/N and healthy subjects. Control samples from healthy subjects with no antibodies incubated in vitro with either anti‐GPA or anti‐Rh were analyzed for neutrophil and monocyte surface activation marker expression, reactive oxygen species (ROS) content, and formation of aggregates with RBCs. Samples incubated with an IgG1 isotype antibody served as controls.ResultsEx vivo, neutrophil CD66b and monocyte CD63 surface expression was increased in patients with auto‐anti‐M/N compared to those with allo anti‐M/N (p = .1757; p = .0698) and to healthy subjects (p = .0186; p = .013). In vitro, neutrophil CD66b and monocyte CD63 surface expression was increased following incubation with anti‐GPA compared to anti‐Rh (p = .0003; p = .0328) and isotype control (p = .000; p = .0062). Intracellular ROS content increased in both neutrophils and monocytes incubated with anti‐GPA compared to anti‐Rh (p = .0012; p = .0693) and isotype control (p = .001; p = .0021). Percentage of neutrophil‐RBC aggregates was decreased when incubated with anti‐GPA compared to isotype control (p < .01).ConclusionsNeutrophils and monocytes in peripheral blood exposed to an antibody directed against GPA on RBC surfaces, such as M or N antigens, may be primed towards an activated phenotype.