= Anti-Serum. Anti-serum is the sera from an immunised person (immunised from the antigen in interest).
It has many in the field of antibody-based techniques, the antibody produced against the antigen can then be purified and studied; anti-sera could also be used to immunise someone else.
However, it does have it's limitations such as: -Once it has been purified, it would become polyclonal instead of monoclonal.
-Once it has been used, someone new would have to be immunised over and over again. (They have overcome this issue by the creation of a hybrid myeloma/B cell).