Thrombopoietin (TPO) is a liver-produced protein that drives megakaryocyte maturation. TPO regulates platelet production and can increase platelet and endothelial reactivity. We investigated the relationship between TPO and the occurrence of thrombocytopenia and thrombosis in patients with systemic lupus erythematosus (SLE).
We undertook a cohort study of SLE patients (n = 98) with clinical data collected simultaneously with sampling for TPO, inflammatory cytokines and autoantibody detection. TPO levels were measured by sandwich ELISA with patients with rheumatoid arthritis (RA) (n = 100) and controls (n = 79) as comparators. Disease associations were evaluated using non-parametric methods.
TPO levels in SLE (median 8 pg/ml, mean 326, range 8992) were moderately increased compared with RA (median 8 pg/ml, mean 100, range 1659, p = 0.07) and controls (median 8, mean 94, range 2088, p = 0.1). Among SLE patients, TPO levels did not correlate with platelet count or levels of antiphospholipid antibodies. The prevalence of thrombocytopenic episodes, thrombotic events or active disease was not increased in patients with high TPO levels. TPO levels correlated with MIP-1α (Rs 0.56, p < 0.001), IL6 (Rs 0.26, p = 0.02) and IL4 (Rs 0.29, p = 0.01), and inversely correlated to C4 (Rs -0.23, p = 0.04). MIP-1α was the strongest independent predictor of increased TPO levels.
TPO levels are elevated in 20% of patients, but are not closely related to the occurrence of thrombocytopenia or thrombosis in SLE. MIP1-alpha is the main factor driving higher TPO levels among patients with SLE, likely through its inhibitory effect on megakaryocyte function.