Absence of antibody to XMRV gp70 in serum from patients with CFS. XMRV gp70 protein was immunoprecipitated from XMRV-uninfected (Un) or XMRV-infected (XMRV) ferret cells using serum from subjects with (CFS) or without (Cont) CFS or with a rat monoclonal antibody to gp70. Immune complexes were separated on 4-20% SDS gels transferred to nitrocellulose membranes and immunoblotted with goat polyclonal antibody to XMRV gp70. (A) Sera from CFS patients 13 and 48, and control subject 22. (B) Sera from CFS patients 59 and 62 and control subject 87. The numbers between the blots are sizes of protein markers in kilodaltons.