Peripheral blood mononuclear cells - Can they provide a clue to the pathogenesis of Graves' Orbitopathy?

Graves' disease (GD) is an autoimmune disorder affecting primarily the thyroid gland. The most common extrathyroidal manifestation of GD is known as Graves' orbitopathy (GO). Bone marrow-derived fibrocytes represent a subset of monocytes in peripheral blood mononuclear cells (PBMCs), infiltrate the orbital tissues, and contribute to the pathogenesis of GO. Hence objectives of the study included whether the concentration of fibrocytes in peripheral blood was higher in GO, whether TSHR m RNA expression and TSHR surface expression in peripheral blood were higher in GO in comparison to Graves' Disease (GD) and Control subjects.

The percentage of circulating fibrocytes (FC) along with TSHR on its cell surface (CD 34⁺, CD 45⁺, CXCR4⁺, Collagen 1⁺, TSHR⁺) were assessed by flow cytometry of 50 patients with GD and GO and 15 healthy donors (Control). TSHR mRNA expression was measured by q RT PCR.

The concentration of circulating fibrocytes was significantly higher in GO compared to GD and control [GO 17% vs GD 3% vs control 0.7% (p < 0.05)]. Moreover, these fibrocytes express a significantly higher level of TSHR in GO. This was corroborated by the measure of TSH mRNA; in GD it was 2.3-fold higher and in GO it was 3.9 fold higher than in control, in GO this transcript level was 1.7fold higher than GD (p < 0.05). TSHR⁺ fibrocytes were significantly positively correlated with CAS (p = 0.004) and negatively correlated with age (p = 0.01) and duration of disease (p = 0.01) in GO.

This study sheds further light on the pathogenesis of GO.