Structure and function of intestinal mucin: developmental aspects.

Mucin glycoproteins are thought to play an important role in protecting the intestine from chemical or physical injury but the mechanisms of protection and the possible relationship between mucin structure and function are incompletely understood. Structurally, purified intestinal mucins are a heterogeneous and polydisperse group of large-molecular-weight glycoproteins which have regional and developmental differences in composition. Newborn mucin contains more protein and less carbohydrate than adult mucin and differs from adult mucin in buoyant density and mobility on electrophoresis. The primary function of mucin, protection of the intestine, appears to be dependent upon at least four factors: the rate and quantity of mucin release; the physical barrier of the viscous mucus blanket; the provision of specific inhibitory binding sites to infectious agents and proteins, and the inclusion of secretory immunoglobulins to provide a link to the immunologic component of the intestinal host defense system. Immune as well as infectious and chemical agents appear to play an important role in mucus release but developmental effects have not been studied. Preliminary studies indicate that developmental differences may exist in the provision of inhibitory binding sites and the inclusion of secretory immunoglobulins in mucin. These studies indicate that mucus may provide a link between the physical and immunological components of the intestinal host defense system and point to the need for further studies in this area.