ABSTRACT
A nonpathogenic filamentous Gram-positive organism which associates with intestinal absorptive cells is frequently found in rodent ileum. Absorptive cells develop an elaborate concentric cytoplasmic specialization in the area of the terminal web immediately surrounding the apical membrane indentation. In thin sections, the zone of absorptive cell specialization consists of three concentric layers which vary in density and texture and are thought to represent different populations of microfilaments. Freeze-fracture replicas reveal a redistribution of absorptive cell apical membrane intramembrane particles (IMPs) at filamentous organism attachment zones. Unperturbed P fracture faces of intestinal absorptive cell plasma membranes generally contain numerous IMPs, there are two absorptive cell membrane domains which normally are relatively devoid of P face IMPs: the apical plasma membrane at the tip of microvilli8 and the lateral plasma membrane immediately subjacent to the intercellular tight junction.
