Human myxovirus resistance protein 1 (MxA) is a key mediator of the interferon-induced response, and BioVendor's immunoassay is suggested as a laboratory marker in two clinical applications. In patients with respiratory tract infection, MxA differentiates patients with a viral infection from patients with bacterial infection and healthy individuals. In patients with multiple sclerosis, low MxA levels reflect reduced efficacy of IFN therapy and are used for therapy monitoring.