Differential properties of mucous glycoproteins in rat nasal epithelium. A comparison between allergic inflammation and lipopolysaccharide stimulation.

To examine the differential properties of mucous glycoproteins, we produced hypertrophic and metaplastic changes in goblet cells of rat nasal epithelium by intranasal instillation of ovalbumin (OVA) in OVA-sensitized rats, and by intranasal lipopolysaccharide (LPS) instillation. The epithelial mucosubstance was quantitatively examined by alcian blue-periodic acid-Schiff (AB-PAS) and lectin histochemistry. The newly produced mucin after OVA challenge or LPS instillation contained a high amount of sulfomucin and a low amount of neutral glycoprotein: LPS-induced mucin contained more sulfomucin (70.1% of total) and less neutral glycoprotein (8.6%) than OVA-induced mucin (sulfomucin, 33.6%; neutral glycoprotein, 41.8%; p < 0.01). Four of the lectins stained some of the mucosubstance, indicating the presence of galactose-N-acetylgalactosamine, alpha2,3- and alpha2,6-linked sialic acid-galactose, and fucose residues. After LPS instillation, the reactivity was higher for galactose-N-acetylgalactosamine (64.8% of total) and alpha2,3-linked sialic acid-galactose (75.8%) than after saline instillation (3.5 and 19.1%, respectively) or OVA challenge (5.8 and 32.3%; p < 0.05). OVA challenge did not induce the alteration of terminal sugar residues. A 2-fold increase in mucin mRNA (rat Muc5ac) expression was induced after LPS instillation or OVA challenge, compared with animals treated with saline instillation (p < 0.05). These results indicate that mucin mRNA expression (for peptide backbone) increases similarly after LPS instillation or OVA challenge; however, carbohydrate compositions of newly produced mucin are different between the two groups.