CD40 and thromboangiitis obliterans: Orbital fibroblasts from patients with TAO expresses CD40 while fibroblasts from patients with non-inflammatory conditions do not.[7] Increased CD40L expression has been observed in T cells derived from the plasma of patients with GD.[8] The CD40-CD40L interaction promotes the production of proinflammatory cytokines, including IL-8 and IL-6.[7] Orbital fibroblasts from patients with TAO also produce cytokines (e.g. IL-6, and IL-8) in response to TSH stimulation, suggesting that circulating antibodies may directly support orbital inflammation.[9, 10]