Ultrastructural localization of fibronectin and laminin in human granulation tissue in relation to capillary development

The distribution of fibronectin (FN) and laminin (LM) at developing capillaries during various developmental stages, from capillary sprouts to relatively developed capillaries, was studied by light- and electron-microscopy immunocytochemistry. By light-microscope, FN immunoreactivity was diffusely distributed throughout the stroma of the granulation tissues, while for LM it was preferentially distributed at the perivascular region with the various developmental stages of the immature capillaries. Ultrastructural study revealed that capillary sprouts were closely surrounded by plentiful deposits of immunoreaction with the FN, but only faintly for LM. Relatively developed capillaries with large and tall endothelium were surrounded by plentiful immunoreactive products with both FN and LM, and immunoreactivities in the cisternae of rER of the endothelium and/or the pericytes were also shown. Cytoplasmic interdigitations between the endothelium and the pericyte of developing capillaries were recognized without an immunoreaction for FN and LM. These results mean that the capillary sprouts are associated with a prepatterned FN-rich and LM-poor perivascular matrix, whereas relatively developed capillaries are associated with a FN- and LM-rich perivascular matrix which would have been produced by the capillary endothelium and/or pericytes.