No abstract

Previous studies have established that the mechanism of species-specific sponge cell reaggregation in vitro involves at least three components: a species-specific aggregation factor, its cell surface receptors, and Ca2+ ions. Here we report about the binding of Microciona 125I-labeled aggregation factor to cells and to other molecules of aggregation factor coupled to agarose beads, as well as the role of divalent cations in both factor-cell and factor-factor interactions. Our results indicate that cell aggregation is a two-step process, involving (1) Ca2+-independent species-specific binding of the 21 X 106 dalton aggregation factor to cellular receptors and (2) formation of Ca2+-dependent linkages between factor molecules on adjacent cells. Quantitation of binding suggests that less than 5% of the cell-associated aggregation factor in vivo is required for cell-cell adhesion in the in vitro assay. Alternative biological functions for the aggregation factor are discussed.

A method was established to quantify MUC5AC in human tear samples obtained on Schirmer strips. There was no correlation between the amount of MUC5AC and age or gender in the healthy population. Dry eye disease patients, however, typically showed reduced concentrations of soluble MUC5AC in the tear film.