Western blot analysis of foetal bovine serum proteins (FBS) by monoclonal antibody produced against the 65-kDa tumour-associated phosphoprotein (p65) isolated from a human breast cancer cell line, showed the presence of an antigenically related (p65-like) protein in FBS. Four protein bands reacting with the anti-p65 monoclonal antibody were detected with an isoelectrofocusing gel (IEF). These four protein bands in SDS-PAGE exhibit the same molecular weight (about 65 kDa) but different isoelectric points (pIs) in IEF. A mixture of the purified isoforms of the p65-like protein was used for the immunization procedure. The usefulness of these anti-p65-like polyclonal antibodies for the immunohistochemical detection of p65 in breast cancer tissues was tested and compared with that of the anti-human-65 monoclonal antibodies. It can be concluded that the polyclonal antibodies obtained may be used in the detection of p65 antigen in breast cancer.
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