PHOSPHORYLATION OF ALPHA1-ACID GLYCOPROTEIN MODULATES BOVINE NEUTROPHIL PHAGOCYTOSIS AND KILLING ACTIVITY

Alpha1-acid glycoprotein (AGP) is a serum protein with a very low pI (2.8-3.8) and a very high carbohydrate content (more than 40%). Bovine AGP (boAGP ) is a 43kDa single polypeptide, 185 aminoacids long. Prosite analysis revealed that boAGP is N-glycosylated in 5 residues and presents 6 potential phosphorylation sites. AGP is an immunocalin, a binding protein that can also exert several immunomodulatory functions. Form a clinical perspective, AGP behave like an acute phase protein, i.e. its serum concentration is increased during systemic response to inflammation. Remarkably, both major (branching) and minor (sialylation) carbohydrate microheterogeneities are modified during systemic inflammation. This study focused on the phosphorylation of AGP, which has been poorly investigated so far. The aim was to elucidate the impact of phosphorylation on AGP’s immunomodulatory functions. Bovine granulocytes were identified as cellular models and one of their most important features were targeted, namely their capability to phagocyte and kill invading bacteria. Isolated bovine granulocytes were incubated with increasing concentrations (0.3-0.6-0.9 mg/ml) of purified native and dephosphorylated AGP (deP-AGP). Native AGP upregulated neutrophil phagocytic activity in a dose-dependent, statistically significant way, the concentration usually found in plasma during acute phase reaction being the most active (i.e. 0.9 mg/ml).