Immunoglobulin G and phosphatidylserine in regenerative and nonregenerative immune‐mediated anemias of dogs

BACKGROUND: Although precursor‐targeted immune‐mediated anemia (PIMA) is thought to be caused by immune targeting of erythroid precursors (nucleated RBCs, nRBCs), its pathogenesis is unknown. Immunoglobulin G (IgG) or phosphatidylserine (PS) may promote nRBC destruction in PIMA. HYPOTHESIS: Dogs with PIMA have increased nRBC IgG and PS, and dogs with immune‐mediated hemolytic anemia (IMHA) have increased RBC PS compared to healthy dogs. ANIMALS: Blood from 20 healthy dogs and from dogs with IMHA (11) or other (non‐IMHA) conditions (9), and marrow aspirates with or without blood from 10 healthy dogs and from dogs with PIMA (17) or other (non‐IMHA, non‐PIMA) conditions (7). METHODS: Marrow nRBC stages were separated by density gradient. Flow cytometry was used to assess the percentage of RBCs or nRBCs with increased IgG or PS. RESULTS: Red blood cell (RBC) IgG positivity was increased in 9/11 IMHA dogs and 0/9 non‐IMHA dogs. Red blood cell PS positivity was increased in 10/11 IMHA dogs and 2/9 non‐IMHA dogs. Five of 17 PIMA dogs had increased nRBC IgG positivity in mid‐ or late‐stage fractions, whereas all 7 non‐PIMA dogs were negative. Mid‐ and late‐stage erythroid precursor PS was significantly higher in PIMA dogs compared to healthy dogs. Five of 14 PIMA dogs had increased RBC IgG positivity. CONCLUSIONS: Immunoglobulin G and PS may promote destruction of nRBCs in PIMA dogs; PS may promote destruction of RBCs in IMHA dogs.