T cells and orbital connective tissue in endocrine orbitopathy

Slit2 Regulates Hyaluronan & Cytokine Synthesis in Fibrocytes: Potential Relevance to Thyroid-Associated Ophthalmopathy

CONTEXT

CD34+ fibrocytes have been implicated in development of thyroid-associated ophthalmopathy (TAO), a consequential autoimmune manifestation of Graves disease (GD). In TAO, CD34+ fibrocytes appear to masquerade as CD34+ orbital fibroblasts mixed with CD34- OF (collectively, GD-OF). Slit2, an axon guidance glycoprotein, is expressed by CD34- OF and attenuates GD-OF gene expression. Cardinal features of TAO include hyaluronan (HA) accumulation and cytokine-driven inflammation.

OBJECTIVE

Compare expression of HA synthase isoenzymes (HAS1-3), UDP-glucose dehydrogenase (UGDH), synthesis of HA, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in fibrocytes and GD-OF. Determine whether Slit2 alters gene expression patterns.

DESIGN/SETTING/PARTICIPANTS

Patients with TAO and healthy donors were recruited from an academic practice.

MAIN OUTCOME MEASURES

Real-time polymerase chain reaction, HA, IL-6, and TNF-α immunoassays.

RESULTS

HA synthesis and release from fibrocytes is substantially lower than in GD-OF. HAS1 expression dominates in fibrocytes while HAS2 in GD-OF. In contrast, HAS2 and UGDH expression dominate GD-OF and localize to CD34- OF. Recombinant human Slit2 (rhSlit2) substantially upregulates HA synthesis and HAS2 expression in fibrocytes but attenuates IL-6 and TNF-α production in these cells. In contrast, knocking down Slit2 in GD-OF reduces HA synthesis and HAS2 and UGDH expression while upregulating IL-6 and TNF-α.

CONCLUSION

The dramatic differences in HA, IL-6, and TNF-α production, and HAS and UGDH expression found in fibrocytes and GD-OF appear, at least in part, to be attributable to Slit2. These findings provide novel insight into the differences in gene expression exhibited by CD34+ fibrocytes and CD34+ OF and therefore reveal important aspects of disease pathogenesis.

Two Cases of Refractory Endocrine Ophthalmopathy Successfully Treated with Extracorporeal Immunoadsorption

Endocrine ophthalmopathy (EO) is a severe disease entity that is characterized by retrobulbar swelling due to accumulation of glycosaminoglycans on an autoimmune basis. This disorder can lead to the loss of vision and often is resistant to conventional therapy. There is a relation to Graves' hyperthyroidism, but probably no close association. Two patients with severe EO that was resistant to usual therapeutic approaches including steroids and radiological and surgical measures underwent a 20 session course of intensive immunoadsorption therapy (Plasmaselect/Therasorb Anti-IgG) with a mean 2- to 3-fold plasma volume treated. After the first sessions, both patients voiced an impressive relief of their major symptoms, which was confirmed by ophthalmological investigation. Throughout the time of therapy until present, these patients have remained at their respective levels of improvement. We consider immunoadsorption an effective therapeutic opportunity in severe EO resistant to conventional treatment.