[Role of glycans in the binding of human serotransferrin and lactotransferrin to human alveolar macrophages].

The optimal conditions of the binding of human lactotransferrin to human alveolar macrophages have been determined and the necessity to measure the binding in absence of bovine serum albumin was demonstrated. In these conditions, diferric lactotransferrin and iron-free lactotransferrin are reversibly bound with the following parameters: association constant Ka = 2 and 5 X 10(6) M-1, respectively, and the number of binding sites N = 1.2 and 1 X 10(7), respectively. The binding of the two forms of lactotransferrins was inhibited by various neoglycoproteins, the highest inhibition being obtained with L-fucosyl, then, in the following decreasing order: D-mannosyl greater than N-acetyl-D-glucosaminyl greater than D-galactosyl. In the same conditions, the binding of serotransferrin (Ka = 2 X 10(7) M-1 and 1.6 X 10(7) M-1; N = 5 X 10(4) and 8 X 10(4) for diferric and iron-free protein, respectively) was not inhibited. These results suggest that the recognition of lactotransferrin is mediated by one or several membrane lectins, the fucose being one of the sugar playing an important role in the association. On the contrary, the binding of serotransferrin does not depend on a membrane lectin system.