Background Despite the realisation that rheumatoid arthritis (RA) is an autoimmune disease there is still considerable interest in the idea that widespread dissemination of synovial fibroblasts with “transformed” characteristics may play a role in polyarticular joint destruction. An animal model indicated that fibroblast-like synoviocytes (FLS) implanted in one location next played a role in cartilage destruction at remote sites with the circulation the most likely conduit(1). In man FLS are thought to be derived from multipotential mesenchymal stromal stem cells (MSCs) and whilst circulating MSCs have been reported in animal models, this is more contentious in man.
Objectives To use simultaneous superficial and deep venous blood in cases undergoing orthopaedic skeletal manipulation of long bones (lower extremity) prior to definitive stabilisation to explore the basis for potential MSC circulation in skeletal injury, health and RA.
Methods Deep (femoral) and matched anticubital vein blood was collected from 36 patients undergoing lower limb orthopaedic procedures. Peripheral blood was also taken from 11 early RA cases (EULAR/ACR criteria) and 12 healthy controls. CFU-F assays were performed on all samples. Cytometric phenotyping and molecular characterisation of genes related to osteo-, chondro- and adipo-genesis were undertaken. To exclude the possibility that CFU-Fs obtained from peripheral vein were merely syringe-trapped fibroblasts, control skin fibroblasts were also used in the molecular analysis.
Results 17/36 femoral vein samples contained CFU-Fs but only 6/59 peripheral vein samples (p=0.0002). Only orthopaedic cases showed peripheral blood MSC circulation which often, but not exclusively, were associated with concomitant presence in the femoral vein. In the 17 femoral vein samples with CFU-Fs their mean frequency was 0.00001% of MNCs. The frequency was higher when sampling post manipulation compared to before/during (9.7x10–8 compared to 3.1x10–8 in femoral vein, 4.0x10–8 compared to 1.2x109 in the periphery). We confirmed the MSC nature of the CFU-Fs by expansion and phenotype: CD105/CD73/CD90 positivity and CD19/CD31/CD33/CD34/CD45/CD61 negativity. Their molecular profiles were typical of MSCs with 39/80 genes (including ALPL, COL1A1, POU5F1, NGFR, SPARC, SOX9) showing similarity across multiple MSC tissue controls (iliac crest and femoral marrow-, cortical bone-, periosteum- and adipose-derived MSCs) and neither had profiles that suggested they represented fibroblasts from dermis.
Conclusions There is no evidence that MSCs circulate in early RA. Although MSCs are present in deep veins their presence appears to be, at least in part, linked to skeletal manipulation. Their numbers are so low that a biological role seems unlikely. Biophysical micro-damage to the trabecular vascular architecture, permitting circulation, is a likely explanation. These findings challenge the idea that circulating MSCs or their progeny play a role in early RA or other autoimmune diseases and also challenges the idea that intravenous injection of MSCs with “homing” to sites of injury is a valid strategy since physiological MSC circulation does not occur naturally to a significant degree.
Nat Med. 2009;15(12):1414
Disclosure of Interest None declared