Monographs in pathology最新文献

The major and rate-limiting barrier to transepithelial permeation in the intestine is the intercellular tight junction. Tight junction structure is often cell type specific and general but imperfect correlates between tight junction structure and permeability exist. The structure and permeability of this key barrier is not static and can be regulated physiologically. The means of regulation appears to involve the cytoskeleton of neighboring epithelial cells (particularly absorptive cells). Meal-related solutes--nutrients such as glucose--can reversibly enhance the permeability of absorptive cell tight junctions. Although this may substantially enhance the ability of the small intestine to harvest meal-related nutrients, it is conceivable that this may also result in transient exposure of the subepithelial compartment to potentially noxious lumenal compounds. Some features found in many intestinal disease states such as PMN migration across the epithelium may also result in transient barrier defects. With PMN transmigration it is clear that even macromolecules may permeate junctions being impaled by PMNs. When disease processes finally result in focal epithelial denudation, the epithelium has the potential of resealing such defects with remarkable efficiency. The preceding discussion highlights how dynamic the tight junction is and sets the stage for future work aimed at understanding the initial signaling events and intracellular cascade(s) that allow this major barrier to demonstrate such plasticity.

Prions are novel, transmissible pathogens causing degenerative diseases in humans and animals. Kuru, CJD, and GSS illustrate the infectious, sporadic, and genetic mechanisms for human prion diseases, respectively. Scrapie of sheep and goats is the prototypic prion disorder since it was the first of these diseases to be transmitted to laboratory rodents. Over the past five years, a large amount of experimental data about the particles causing scrapie has been accumulated. Most of the information has been confirmed, and much of it is widely accepted. At times, this confirmed body of information has been overshadowed by what appears to be controversy due to the diverse terminology used by different laboratories. Prions are composed largely, if not entirely, of an abnormal isoform of the prion protein (PrP). The development of procedures to disperse infectious prions in detergent-lipid-protein complexes (DLPC) and liposomes has led to many advances. Previously, purified prions were aggregated into rod-shaped particles which are insoluble amyloids. Monoclonal antibodies (mAb) raised against PrP 27-30, which is derived from the scrapie PrP isoform (PrPSc) by limited proteolysis. have been used to purify scrapie prion infectivity in DLPC. Immunoaffinity purified fractions contain PrPSc and high prion titers. Polyclonal antibodies to PrP 27-30 were found to neutralize scrapie infectivity. These experimental results coupled with additional biochemical, genetic, pathologic, and cell biological lines of evidence have established that PrPSc is a major and necessary component of the scrapie prion. Both PrPSc and its cellular isoform (PrPc) are encoded by the same single-copy chromosomal gene. This is a major feature distinguishing prions from both viruses and viroids. To date, no prion-specific nucleic acid has been identified that is required for transmission of disease. PrPC and PrPSc are thought to have the same amino acid sequence but to differ due to some posttranslational process. Both PrPC and PrPSc are glycoproteins that possess Asn-linked oligosaccharides and glycosyl phosphatidylinositol (GPI) anchors. Whether the features that distinguish PrPSc from PrPC arise from differences in their Asn-linked oligosaccharides or GPI anchors is unknown. GSS and familial CJD are the only known human diseases that are both genetic and infectious. Recent studies have demonstrated that GSS is an autosomal dominant disorder and that a Pro----Leu substitution at codon 102 of the PrP gene is linked to the development of GSS. Earlier investigations showed genetic linkage between an incubation time gene (Prn-i) and the PrP gene in inbred mice.(ABSTRACT TRUNCATED AT 250 WORDS)