Co-expression of S1P3 and glial fibrillary acidic protein (GFAP) on all reactive astrocytes in MS lesions and surrounding tissues was confirmed by double-immunostaining (Fig. 2A), but only small numbers of S1P3-expressing CD68-positive macrophages could also be detected (data not shown). The gene discussed is GFAP; the disease is myeloid sarcoma.