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The migration of growth cones on substrates consisting of naturally occurring cell adhesion molecules has been extensively studied in cell culture. However, relatively little is known about how growth cones contact the substrate or how the patterns of contact change as growth cones move forward. We have examined the interactions of chick retinal ganglion cell growth cones with laminin, merosin, N-cadherin, L1 and poly- l -lysine by time-lapse interference reflection microscopy (IRM) using a laser scanning confocal microscope. In images obtained by IRM, areas of a cell that are closely apposed to the substrate appear dark whereas areas that are farther away appear light. Growth cones on laminin and merosin were almost uniformly light, indicating that very little of the membrane was in close contact with the substrate. Growth cones on N-cadherin had a mottled appearance with some relatively large dark gray areas. The proximal portions of filopodia often were dark, in contrast to those on laminin and merosin which were light. In addition, growth cones on N-cadherin had numerous dark gray punctate regions of close association with the substrate. Growth cones on L1 had darker regions than growth cones on other substrates and these comprised a larger fraction of their area. There also were differences in the temporal dynamics of growth cone interactions with different substrates and these differences correlated with differences in rates of growth. None of the contacts observed in growth cones were as dark or stable as focal contacts of fibroblasts.

Inflammatory bowel disease (IBD) is a chronic disorder whose etiology is linked to triggering events, including viral infections, that lead to immunoregulatory dysfunction in genetically susceptible people. Characteristic pathological changes include increased mononuclear leukocyte influx into the intestinal mucosa as well as mucosal smooth muscle cell (M-SMC) hyperplasia. Virus infection or viral mimic [polyinosinic acid:polycytidylic acid (polyI:C)] treatment of human colon M-SMCs in vitro increases cell surface hyaluronan (HA), and nonactivated mononuclear leukocytes bind to virus-induced HA structures by interactions that involve the HA-binding receptor CD44. In this study, confocal microscopy reveals increased HA on poly I:C-treated M-SMC surfaces within 3 hours, arrayed in coat-like structures. By 17 hours, novel, lengthy cable structures are evident, and these are primarily responsible for mediating leukocyte adhesion. Immunohistochemical staining demonstrates components of the inter-alpha-trypsin inhibitor (IalphaI) complex in both coat-like and cable structures. M-SMCs co-treated with polyI:C and a polyclonal antibody to IalphaI display HA in coats but with diminished cables, and they bind significantly fewer leukocytes than M-SMCs treated with polyI:C alone. Western blot data suggest that heavy chains of IalphaI are specifically associated with cable structures. Staining of tissue sections from patients with IBD demonstrates the presence of HA in inflamed colon tissue, and shows that HA-associated IalphaI staining increases in the mucosa of inflamed IBD specimens compared to noninflamed sections from the same patient, establishing a probable link between the observations in vitro and the progression of the inflammatory process in IBD.