PB1346 - A new canine thrombopoietin assay reveals common pathogenesis of canine and human immune thrombocytopenia

Background: Measuring thrombopoietin (TPO) levels in thrombocytopenic patients provides mechanistic insights into the cause of thrombocytopenia. Domestic dogs are important models of naturally occurring and induced thrombocytopenia syndromes, yet TPO levels in these dogs are unknown due to lack of a canine TPO assay.

Aims: Develop an immunoassay to measure canine plasma TPO concentration and characterize TPO levels in dogs with immune thrombocytopenia (ITP) and non-immune thrombocytopenia.

Methods: Monoclonal antibodies were raised to canine recombinant TPO and used to configure a sandwich ELISA with streptavidin-biotin detection. Assay performance was evaluated, and plasma TPO concentration measured in healthy dogs, dogs with ITP induced by anti-GpIIb antibody infusion, dogs enrolled in a cohort study of naturally occurring ITP, and dogs with thrombocytopenia associated with inflammatory, neoplastic, or bone marrow disorders.

Results: TPO assay performance and plasma TPO concentration and platelet counts in healthy and thrombocytopenic dogs are summarized in Tables 1 and 2. The TPO assay limit of detection was approximately 20 pg/mL (limit of quantitation 50 pg/mL). The TPO levels in healthy dogs were typically < 50 pg/mL, and all dogs with non-immune thrombocytopenia had values within the healthy dog range (Table 2). All dogs with induced ITP responded with marked increases in TPO levels by 5 to 10 days after antiplatelet antibody infusion. In contrast, high TPO was uncommon in dogs with naturally occurring ITP with only 2 dogs (3%) having TPO >200 pg/mL and 42 dogs (72%) having TPO < 50 pg/mL .

Conclusion(s): Naturally occurring ITP in dogs is characterized by inappropriately normal TPO levels, suggesting that ineffective thrombopoiesis contributes to severe thrombocytopenia in these patients. This shared clinicopathologic feature of canine and human ITP confirms the value of cross-species, comparative studies of ITP pathogenesis and treatment response.
Funded by Morris Animal Foundation Grant D18CA-821