Autoantibodies to thrombopoietin and the thrombopoietin receptor in patients with immune thrombocytopenia.

Summary: Autoantibodies to thrombopoietin (TPO, also termed THPO) or the TPO receptor (cMpl, also termed MPL) could play a pathological role in immune thrombocytopenia (ITP). In this study, we tested for autoantibodies against TPO, cMpl, or the TPO/cMpl complex in ITP and other thrombocytopenic disorders. Using an inhibition step with excess TPO in fluid‐phase to improve binding specificity, the prevalence of anti‐TPO autoantibodies was: active ITP: 9/32 (28%); remission ITP: 0/14 (0%); non‐immune thrombocytopenias: 1/10 (10%); and healthy controls: 1/11 (9%). Similarly, using an inhibition step with excess cMpl, the prevalence of specific anti‐cMpl autoantibodies was: active ITP: 7/32 (22%); remission ITP: 1/14 (7%); non‐immune thrombocytopenias: 3/10 (30%); and healthy controls: 0/11 (0%). Two active ITP patients had autoantibodies against the TPO/cMpl complex, but not against TPO or cMpl alone. Anti‐TPO or anti‐cMpl autoantibodies were found in 44% of ITP patients, and in 40% of patients with other thrombocytopenic disorders. These autoantibodies did not correlate with ITP disease severity or number of ITP treatments received; however, in this cohort, 3 patients failed to respond to TPO receptor agonist medications, and of those, 2 had anti‐TPO autoantibodies. This suggests that anti‐TPO and anti‐cMpl autoantibodies are associated with thrombocytopenia, and may be clinically relevant in a subset of ITP patients. [ABSTRACT FROM AUTHOR]