Phenotypic expression of proteoglycan in mast cells of the human nasal mucosa

Summary The phenotypic expression of the proteoglycan of human mast cells in the nasal mucosa and normal skin was analysed using histochemical techniques. Nasal mucosa was obtained from normal subjects, from patients with seasonal allergic rhinitis before and during the pollen season and from patients with nasal polyps. In the latter groups, specimens were taken from both polyp tissue and adjacent nasal mucosa. Formaldehyde treatment blocked the cationic dye binding in 75–84% of the mast cells located in the nasal mucosa, as compared to the optimum fixation with IFAA (iso-osmotic formaldehyde-acetic acid). A significantly lower degree of blocking of dye binding was obtained in the human skin where 45% of the mast cells were susceptible to formaldehyde treatment (P<0.01). The mast cells of the polyp tissue also showed a relatively low degree of blocking (54%), which was significantly lower than the blocking of mast cells of the nasal mucosa taken from the same individuals (P<0.05). Staining of serial tissue sections in Alcian Blue containing graded concentrations of MgCl₂ was used to determine the critical electrolyte concentration (CEC) of the dye binding, defined as the salt concentration at which the staining of 50% of the mast cells is extinguished. The CEC of the skin mast cells was 0.64m MgCl₂ which is significantly higher than that of the mast cells of the nasal mucosa of normal subjects 0.49m (P<0.05)], allergic subjects 0.52m (P<0.01)], patients with polyp disease 0.52m (P<0.01)] and the polyp tissue proper 0.57m (P<0.05)]. This implies that mast cells of the nasal mucosa contain glycosaminoglycans of a relatively lower charge density and/or molecular size than the connective tissue mast cells found in the human skin. A similar difference has been observed between rat mucosal mast cells, containing a chondroitin suphate proteoglycan, and rat connective tissue mast cells which contain a heparin proteoglycan. However, unlike the rat mucosal cells, the mast cells of the human nasal mucosa showed a weakly fluorescent Berberine binding and, like the rat connective tissue mast cells, entirely lost the ability to bind Toluidine Blue after treatment with nitrous acid. Such treatment results in a deaminative cleavage of heparin and heparan sulphate, but does not degrade chondroitin sulphate. These results provide further evidence of the existence of a distinctive mucosal mast cell phenotype also in man. It is suggested that the lower CEC of the mucosal mast cells is an expression of a content of haparan sulphate, while the relatively higher CEC of the skin mast cells is compatible with a content of heparin.