Detection, quantitation, and localization of bovine angiogenin by immunological assays

Bovine angiogenin (bAng) is a potent blood vessel inducing protein found in bovine serum and milk. Antisera have been raised against bAng. Western blot analysis for bAng indicated that the polyclonal antibody recognized bAng specifically, and no cross-reactivity with bovine RNase A, a protein homologous to bAng, was observed. The sandwich enzyme-linked immunosorbent assay for bAng was sensitive to 10 pg of bAng, and this assay was able to quantitate bAng in bovine serum (100-180 ng/mL) and milk (4-8 micrograms/mL). Strong positive immunohistochemical reactions were detected in alveolar cells, the secretion of alveolar cells and excretory ducts in sections of cow mammary gland, epithelial cells of visceral peritoneum and bile-duct in sections of cow liver, and epithelial cells and mucous glands in sections of cow gallbladder. These results suggest that epithelial cells and secretory cells are major sites of angiogenin synthesis.