Characterization of expression of glycan ligands for Siglec-F in normal mouse lungs

Sialic acid-binding immunoglobulin-like lectin (Siglec)-F, an inhibitory receptor on mouse eosinophils, preferentially recognizes the glycan ligand 6'-sulfated sialyl Lewis X, but little is known about the requirements for its lung expression. RT-PCR and immunohistochemistry were used to detect and localize the sulfotransferase keratin sulfate galactose 6-O sulfotransferase (KSGal6ST, also known as carbohydrate sulfotransferase 1; gene name, Chst1) that is putatively required for 6'-sulfated Sialyl Lewis X synthesis. RT-PCR detected the greatest constitutive expression of Chst1 in lung, liver, and spleen tissue. Immunohistochemistry localized the expression of KSGal6ST in lung tissue primarily to airway epithelium. Siglec-F-Ig fusion protein selectively bound in a similar pattern, and was unaffected in lung tissue treated with methanol or deficient in Type 2 α2,3 sialyltransferase (St3gal2), but was eliminated by proteinase K or sialidase, and was absent in tissue deficient in the Type 3 α2,3 sialyltransferase (St3gal3). Binding of the Siglec-F-Ig fusion protein was similar in pattern to, and completely blocked by, a plant lectin recognizing α2,3-linked sialic acid. Thus, α2,3-linked sialic acid-containing glycoprotein Siglec-F ligands and the enzymes required for their synthesis are constitutively expressed in murine lungs, especially by airway epithelium. St3gal3, but not St3gal2, is required for constitutive Siglec-F ligand synthesis. The survival of eosinophils entering the lung may be shortened by encountering these Siglec-F sialoside ligands.