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.