No answer to the lack of specificity: mouse monoclonal antibody targeting the angiotensin II type 1 receptor AT 1 fails to recognize its target

Numerous antibodies targeting G protein-coupled receptors (GPCRs) have been described as non-specific among the polyclonal antibodies against angiotensin II type 1 receptor (AT 1 ). We have tested the newly developed AT 1 receptor mouse monoclonal antibody for its specificity. Human embryonic kidney (HEK293) cells, which do not endogenously express AT 1 receptor, were transfected in order to overexpress a fluorescently labeled enhanced green fluorescent protein (EGFP)-tagged human AT 1 receptor. Western blot and immunofluorescence assays were performed to test the specificity of the Santa Cruz monoclonal antibody sc-57036. These results were compared to the ones obtained with the polyclonal sc-1173 anti-AT 1 receptor antibodies that have already been described as non-specific. While the positive controls using GFP antibodies detected the EGFP-tagged AT 1 receptor, both polyclonal and monoclonal anti-AT 1 receptor antibodies failed to specifically recognize the corresponding band by Western blot, as similar bands were revealed in either transfected or non-transfected cells. It also failed to detect AT 1 receptor in immunofluorescence experiments. The lack of target recognition of the monoclonal AT 1 receptor antibody in our experimental conditions suggests that this antibody could give misleading results such as misidentification of the protein. To our knowledge, no specific antibodies targeting AT 1 receptors have been developed so far and the field is thus in need of new technical developments.