The recognition of the cell-surface carbohydrate on neutrophils is the first stage of their migration out of the blood at sites of infection. Specialized transmembrane proteins (called lectins) are made by cells lining the blood vessel (called endothelial cells) in response to chemical signals emanating from the site of infection. These proteins recognize particular groups of sugars carried by glycolipids and glycoproteins on the surface of neutrophils circulating in the blood. The neutrophils consequently stick to the blood vessel wall. This association is not very strong, but it leads to another, much stronger protein-protein interaction (not shown) that helps the neutrophil migrate out of the bloodstream between the endothelial cells into the tissue at the site of infection.  Fair Use and Copyright info