The present inventors have developed and disclose herein methods of detecting antibody against the gammaretrovirus Xenotropic Murine Leukemia Virus-Related Virus (XMRV) in a subject. Furthermore, the present inventors have established that a diagnosis of a neurological disease such as a neuroimmune disease, or a lymphoma in a subject can correlate with infection with XMRV. In various aspects, a subject can be a person having, suspected of having, or at risk for developing an XMRV-related disease.