Haptoglobin comprises about 10% of granule protein extracted from bovine granulocytes isolated from healthy cattle

Haptoglobin (Hp) is a plasma protein with haemoglobin binding capacity important in maintaining the iron homeostasis and in disease processes influenced by iron metabolism. In cattle Hp is one of the major acute phase proteins, and increases rapidly during infectious disease. At acute clinical mastitis in dairy cows the Hp concentration increases markedly both in blood and milk. Hepatocytes are considered to be the main origin of Hp, but expression of Hp mRNA has also been found in the mammary gland and leukocytes in healthy cattle. In the present study we show that bovine granulocytes, isolated from peripheral blood of healthy cattle, contain abundant amounts of Hp within the granules. As shown by two-dimensional gel electrophoresis (2-DE) in combination with matrix assisted laser desorption ionization-time of flight–mass spectrometry (MALDI-ToF–MS) bovine granulocyte Hp consists of two sets of peptides ca. 20 kDa (α-chains) and ca. 40 kDa (β-chains) with multiple iso-forms.