CD40 and thromboangiitis obliterans: Feldon et al. [15] demonstrated the involvement of T cells and orbital fibroblasts in an antigen-dependent positive feedback loop where autoantigen presentation by fibroblasts through MHC class II and CD40-CD40L ligand leads to the activation of T cells; these activated T cells stimulate fibroblasts to proliferate, resulting in fibroblast-related disorders in TAO.