Rheumatoid arthritis (RA) affects ~1% of the UK population, is painful and significantly disrupts quality of life. Despite recent treatment advances, and improved outcomes, chronic pain can still develop, despite treatment-controlled inflammation1. Vascular endothelial growth factor-Axxxa (VEGF-A) isoforms are pro-inflammatory, pro-angiogenic and pro-nociceptive, and VEGF-A is found in the serum and synovial fluid of RA patients. Systemic anti-VEGFR2 prevents secondary hypersensitivity in mono-arthritis, but local anti-VEGFR2 has no effect, suggesting a central action of VEGFR2 in the development of pain2. Reduced number of ICAM-1-positive blood vessels in the spinal cord suggested an inhibitory action on spinal endothelial activation in these animals2. Hypothesis: targeting VEGFR2 affects pain behaviours through an inhibitory action on spinal cord endothelial activation. Inducible, endothelial-specific VEGFR2 KO mice were generated by crossing Tie2-CreERT2 (EMMA MGI:2450312) and VEGFR2-flox mice. Inducible and endothelial specificity of the KO was confirmed by PCR and VEGFR2 RT-digital droplet (dd)PCR following lung CD31+ve cell selection. VEGFR2fl/fl Tie2-Cre+/- and control mice were subjected to 5 injections of tamoxifen (TAM) (1mg/100mL i.p. o.d.) to induce KO. Articular inflammation was induced by s.c. peri-articular ankle joint CFA injection (160mg/80mL mineral oil) under isoflurane anaesthesia (2-3% in O2). This dose of CFA causes ipsilateral inflammation of the ankle joint, and altered ipsilateral and contralateral sensitisation3. The KO gene sequence was detected in CD31+ lung cells from TAM dosed VEGFR2fl/fl Tie2Cre+/- mice (n=4). The KO gene sequence was not detected in TAM treated control mice (n=4). RT-ddPCR indicated that TAM reduced VEGFR2 mRNA levels (55%) in lung CD31+ cells. In control (cont) mice CFA caused ipsilateral mechanical allodynia (MA) and thermal hyperalgesia (TA) from day 2 and contralateral MA from day 5 onwards. KO mice developed significant ipsilateral MA from day 5 onwards and did not develop significant contralateral MA or TA on either hind paw throughout the study (day 2 ipsi-MA: cont 0.34±0.11g vs KO 1.08±0.10g, p<0.0001; contra-MA day 5: cont 0.83±0.03g vs. KO 1.52±0.04g, p<0.0001; day 2 ipsi-TA: cont 31.9±3.5% of baseline, p<0.05 vs. KO 78.2±25% non-sig from baseline). No KO effect was observed on joint swelling. These findings indicate that endothelial VEGFR2 contributes to nociceptive sensitisation. Together with our previous study these results support the hypothesis that endothelial VEGFR2 plays a role in central sensitisation, contributing to secondary hypersensitivity. Targeting endothelial VEGFR2 may prevent and/or alleviate pain experienced by patients with inflammatory conditions including RA. Funded by Arthritis Research UK. VEGFR2-flox mice gift from M.Hirashima, Kobe University.