Specificity of antibodies to nitric oxide synthase isoforms in human, guinea pig, rat, and mouse tissues

Ten commercially available rabbit polyclonal anti-NOS antibodies were tested for their immunohistological applicability in normal human, guinea pig, rat, and mouse organs. Most antibodies reacted as expected and described in the literature with various tissues of the investigated species. Several antibodies did not react with the expected cell populations in a certain species, or reacted in previously unknown patterns. In addition, different antibodies to the same isoform rarely detected identical cell populations, even within one species. Most of these unexpected immunoreactivities were observed in bronchial epithelial, glomerular epithelial, and vascular smooth muscle cells. These unexpected results usually occurred when the antibodies were tested in other organs or species than that to which they were originally raised. We therefore strongly recommend the use of anti-NOS antibodies only after careful immunohistological and biochemical analysis of their reactivity in the organ and species to be studied.