Thrombopoietin levels increased in patients with severe acute respiratory syndrome

Hematological changes in patients with Severe Acute Respiratory Syndrome (SARS) are common and frequently include thrombocytopenia. Using a ELISA method, we found an increase in thrombopoietin (TPO) levels in the plasma of convalesced SARS patients (290 ± 53 pg/ml) and active SARS patients (251 ± 23 pg/ml) comparing to that from normal control patients (228 ± 17 pg/ml). In addition, the plasma from active SARS patients had an inhibitory effect on CFU-MK formation, which could be neutralized by anti-TGF-β antibodies. In the experiment to determine whether SARS-CoV can directly infect hematopoietic stem cells and megakaryocytic cells, incubation of the cells with SARS-CoV did not show active infection. Our findings of increased TPO levels in the plasma of SARS patients provide a possible explanation for the genesis of thrombocytosis, which frequently develops from thrombocytopenia in SARS patients.