Anisha: Everything is possible, but needs to be carefully proved. ELISA is one of the approaches to prove this circulating Ag, and Western blotting is another. You can use your Ab to make an immunoaffinity column to purify this Ag to confirm its existence, and in return, use to get purified auto-Ab in the same manner. Check out our paper for reference (PMID: 22949401 or download from my RG account). Good luck.