Circulating levels of HPCs expressing VEGFR1 and CXCR4 are increased in peripheral blood of HJD subjects. (A) mRNA from the peripheral blood of HJD subjects (prospective cohort as defined in “Subjects and samples”) show significant up-regulation of VEGFR1 mRNA (labeled Flt-1 mRNA, mouse equivalent of human VEGFR1; P < .001; A) and CXCR4 (P < .01; B) compared with controls (CNTRLs, control group A). Results represent data from 3 experiments. (C) Circulating HPCs (VEGFR1⁺/CD11b⁺) are elevated 4-fold in the peripheral blood of HJD subjects compared with controls by flow cytometry. (D) HPCs, which express CD34/VEGFR1-early myeloid cells, were also increased 4-fold in HJD subjects compared with control group A (BC) and control group B (CNTRLs) by flow cytometry. (E) PBMCs from subjects with HJD increased synovial cell proliferation by 2.5-fold compared with medium alone (DMEM) and control groups A and B (CNTRLs). THP-1 cells (immortalized cells of the monocyte/macrophage lineage used as a positive control) stimulated synovial proliferation up to 1.5-fold (THP-1). These results are expressed as a percentage change compared with the controls. (F) Synovial proliferation by PBMCs from HJD subjects (prospective cohort) could be abrogated by Avastin (Avast), an inhibitor of VEGF, by 50% using 2 different concentrations (0.25 mg/mL, 0.5 mg/mL) of the drug. These results are expressed as number of cells before and after treatment with Avastin.