Neutrophil Extracellular Traps in Plasma from Dogs with Immune-mediated Hemolytic Anemia

Background: Neutrophil extracellular traps (NETs) are part of the innate immune response and are essential in local pathogen control, but are associated with pathological inflammation, organ damage, autoimmunity, and thrombosis. Immune-mediated hemolytic anemia (IMHA) is a pro-inflammatory, prothrombotic disease associated with high mortality. Hypothesis/Objectives: Neutrophil extracellular traps (NETs) are a feature of the inflammatory process in dogs with IMHA. The objective of the study was to evaluate plasma from dogs with IMHA for the presence of 2 indirect markers and 1 direct marker of NETs. Animals: Healthy client-owned dogs (56) and hospitalized dogs with IMHA (n = 35). Methods: Prospective study. Plasma samples for all dogs were evaluated for cell-free DNA using a fluorescence assay, histone-DNA (hisDNA) complex using an ELISA, and citrullinated histone H3 (specific for NETosis) using Western blot. Reference intervals were generated using plasma from healthy dogs. Results: In dogs with IMHA, cell-free DNA concentration was above the reference interval in 17% of samples with a median (range) of 1.0 μg/mL (0.1–17.3), and hisDNA concentration was above the reference interval in 94% of samples with a median (range) of 30.7 × pooled normal plasma (PNP; 0.6–372.1). Western blot for citrullinated histone H3 identified detectable bands in 84% samples from dogs with IMHA. Conclusions and Clinical Importance: The assay for cell-free DNA detected evidence of NETs in fewer dogs than did the other approaches. Excessive NETs appears to be a feature of IMHA in dogs and contributions to the prothrombotic state deserve further study.