A protein complex isolated from its natural medium and including the ZEBRA protein of sequence SEQ ID NO: 1, the isolated protein complex having the following properties: it is more stable than the ZEBRA protein, in particular it is more resistant to the action of the proteases than the ZEBRA protein, it is capable of specifically binding the AZ125 and AZ130 monoclonal antibodies, it is soluble in a body fluid, and in particular a body fluid selected from the group constituted by blood and serum, and to its detection process and the uses of this process for the prognosis or diagnosis of lymphoproliferative episodes associated with the EBV.