B7-1 is induced in numerous pathological settings, including microglia of MS lesions (Williams et al., 1994, De Simone et al., 1995), in human embryonic tissue in response to IFN-gamma (Satoh et al., 1995) and in B cells and monocytes from MS patients (Svenningsson et al., 1997). Here, IFNG is linked to myeloid sarcoma.