Altered sialyl- and fucosyl-linkage on mucins in cystic fibrosis patients promotes formation of the sialyl-Lewis X determinant on salivary MUC-513 and MUC-7

Destruction of the lungs as a consequence of recurrent infections with micr oorganisms such as Psendomonas aeruginosa remains the underlying cause of m ost morbidity and mortality in cystic fibrosis (CF). We have hypothesized t hat changes in the glycosylation of key tracheal mucins such as MUC513 and MUC7 might increase the risk of pulmonary disease in CF patients. However, in preference to sputum we have examined the sugar-chains on these mucins i n saliva because in the latter not only can the glycoproteins be collected from controls, but they are essentially free from modifications made follow ing bacterial infection in disease. Proteins in ductal or whole-mouth saliv a from 20 CF patients with the DeltaF-508 CFTR mutation and age-and sex-mat ched controls were separated by SDS-PAGE and blotted onto nitrocellulose an d then probed with labelled lectins of known specificity. Linkage of termin al sialic acid on the blotted mucins was determined using Sambucus nigra, a gglutinin (detects the 2 -->6 linkage) and Maackia amurensis agglutinin (th e 2 -->3 linkage). Fucose was detected by Ulex europaeus agglutinin-1 (1 -- >2 linkage) and Aleuria aurantia agglutinin (1 -->3 linkage). We found that each mucin shows a characteristic glycosylation pat-tern and in controls m ost of the sialic acid is 2 -->6 linked on MG1 (MUC 513) and 2 -->3 linked on MG2 (MUC 7). CF is associated with a shift from a 2 -->6 linkage to a 2 -->3 linkage on MG1 with some patients showing almost no 2 -->6 linkage; 2 -->3 linkage on MG2 is similarly increased in disease in some individuals. The expression of fucose on these mucins is also raised in CF patients. The se shift to a 2 -->3 linkage of sialic acid, and with increased fucosylatio n this promotes the formation of sialyl-Lewis X antigen detected on CF muci ns in our study. These changes will be tested for their correlation with th e severity of lung disease. We gratefully acknowledge support from the Euro pean Union Biomed-II Programme.