Other studies reported a fall in serum neopterin levels or in the levels of other IFN biologic response markers, including matrix metalloproteinases (MMPs), beta2 microglobulin, MxA, viperin, TNF-related apoptosis-inducing ligand (TRAIL) and X-linked inhibitor apoptosis factor-1 (XAF-1), when NAb titers were elevated in patients with MS [6,20,38-41]. The gene discussed is XAF1; the disease is myeloid sarcoma.