Association of Circulating Fibrocytes With Fibrostenotic Small Bowel Crohn's Disease.

BACKGROUND: Fibrocytes are hematopoietic cells with features of mesenchymal cells found in the circulation and inflammatory sites implicated in promoting fibrosis in many fibroinflammatory diseases. However, their role(s) in the development of intestinal fibrosis is poorly understood. Here, we investigated a potential role of fibrocytes in the development of fibrosis in Crohn's disease (CD) and sought factors that may impact their development and function. METHODS: Plasma and mononuclear cells were collected from patients with and without fibrostenotic CD. Fibrocytes defined as CD11b+, CD34+, and Collagen 1+ were correlated with clinical assessments of fibrosis, including evaluation using intestinal ultrasound. We measured the levels of relevant circulating molecules via Luminex and studied the effect of patient plasma proteins on fibrocyte differentiation. RESULTS: Fibrocyte numbers were increased in CD patients with stricturing Crohn's disease compared with patients with an inflammatory phenotype (P = .0013), with strong correlation between fibrocyte numbers and acoustic radiation force impulse (ARFI), a measure of bowel elasticity on intestinal ultrasound (R = .8383, P = .0127). Fibrostenotic plasma was a more potent inducer of fibrocyte differentiation in both primary human monocytes and cell line and contained increased levels of cytokines implicated in fibrocyte differentiation compared with plasma from inflammatory patients. Interestingly, increased fibrocyte numbers at time of ultrasound were associated with escalation of medical therapy and endoscopic/surgical management of small bowel strictures at 30 months follow-up. CONCLUSIONS: Circulating fibrocytes strongly correlate with fibrostenotic disease in CD, and they may serve as predictors for escalation of medical +/- surgical therapy.

Intestinal strictures are thought to result from excessive deposition of extracellular matrix by activated mesenchymal cells. In this study, we provide evidence that supports a potential role of fibrocytes (bone marrow­derived mesenchymal precursors) in collagen deposition in Crohn's disease strictures. Inasmuch as fibrocyte numbers correlate with sonographic measures of bowel stiffness, fibrocyte numbers may predict the need for therapy escalation.