Intravenously injected sialidase inactivates attachment sites for lymphocytes on high endothelial venules

Blood-borne lymphocytes initiate entry into secondary lymphoid organs, such as peripheral lymph nodes (PN) and gut-associated Peyer's patches (PP), by a highly specific adhesive interaction between the lymphocytes and the endothelium of specialized blood vessels known as a high endothelial venules (HEV). The selectivity with which functional subpopulations of lymphocytes migrate into particular lymphoid organs is believed to be regulated by the expression of cell adhesion receptors and complementary ligands on lymphocytes and HEV, respectively. The entry of lymphocytes into PN and PP has clearly been shown to involve distinct receptor-ligand pairs. Employing the Stamper-Woodruff in vitro adhesion assay, which measures lymphocyte attachment to HEV in cryostat-cut sections of lymphoid organs, we have previously shown that treatment of PN sections with two different sialidases inactivates HEV-adhesive ligands, whereas treatment of PP tissue sections has no effect on HEV-adhesive function. We now report that in vivo exposure of HEV to sialidase (after i.v. injection of the enzyme) also selectively prevents subsequent in vitro attachment of lymphocytes to PN HEV but not to PP HEV. Consistent with this organ-selective impairment of HEV-adhesive function by sialidase, i.v. injection of the enzyme is shown to prevent short term lymphocyte accumulation within peripheral lymph nodes while having no significant effect on accumulation in PP, blood, or nonlymphoid organs. Histologic examination with the sialic acid-specific lectin from Limax flavus verified that i.v. injected sialidase effectively removes stainable sialic acid moieties from HEV in both PN and PP. This study confirms that sialic acid is required for the adhesive function of PN HEV-ligands. A role for sialic acid as either a recognition determinant or as a regulatory molecule can be envisioned. In view of the fact that many pathogens release sialidase and cause substantially elevated serum levels of this enzyme, the present observations may have pathophysiologic significance. One mechanism by which such pathogens may avoid destruction is to inactivate susceptible HEV-ligands and disrupt the entry of lymphocytes into lymphoid organs where immune responses against the pathogens would normally be initiated.     

黄土高原地区提取植被信息方法的研究

研究评价了适于黄土高原地区植被信息提取的最佳植被指数和方法。该地区分布有落叶阔叶林、草原和荒漠,植被类型丰富多样。然而土壤背景对植被信息提取有较大影响。经对比分析,修正后的土壤调节植被指数（ＭＳＡＶＩ）, 不仅能增强植被信号,并能大大减小土壤背景的影响,同时又能宏观地反映该地区植被类型的分布状况。它是黄土高原地区目前提取植被信息较好的植被指数。标准化差值植被指数（ＮＤＶＩ）、土壤调节植被指数（ＳＡＶＩ）和垂直植被指数（ＰＶＩ）分别适用于高密度、中等密度和稀少植被地区植被信息的提取和监测。各种植被指数多时象累加产生的图像能较好地提取植被信息     

Substance P and neurokinin A metabolism by cultured human skeletal muscle myocytes and fibroblasts

A recent study determined that cultured human skeletal muscle adult myoblasts, myotubes, and fibroblasts degraded angiotensins and kinins via neutral endopeptidase-24.11 (NEP-24.11; EC 3.4.24.11) and aminopeptidase N (APN; EC 3.4.11.2). Due to the possible importance of other peptides to skeletal muscle blood flow and function, the present study looked specifically at the metabolism of the neurokinins substance P (SP) and neurokinin A (NKA) by skeletal muscle peptidases. The results show that SP is degraded not only by NEP-24.11, but also sequentially by dipeptidyl(amino)peptidase IV (DAP IV; EC 3.4.14.5)/APN. NKA is unaffected by DAP IV but is metabolized by NEP-24.11 and APN. NEP-24.11 was inhibited by phosphoramidon (IC₅₀ = 80 nM), thiorphan and ZINCOV, DAP IV by diprotin A (IC₅₀ = 8 μM), and APN by amastatin (IC₅₀ = 50 nM) and bestatin (IC₅₀ = 100 μM). Skeletal muscle myocyte and fibroblast metabolism of SP and NKA may regulate local skeletal muscle vascular and extravascular functions including SP- and NKA-mediated nerve-induced vasodilation. Inhibition of both NEP-24.11 and DAP IV/APN may increase skeletal muscle blood flow and decrease peripheral vascular resistance via potentiation of local neurokinin levels.     

Investigation of the role of the disulphide bond in the activity and structure of staphylococcal enterotoxin C1

The goal of this study was to Investigate the role of the disulphide bond of staphylococcal enterotoxin C1 (SEC1) in the structure and activity of the toxin. Mutants unable to form a disulphide bond were generated by substituting alanine or serine for cysteine at positions 93 and/or 110. Although we did not directly investigate the residues between the disulphide linkage, tryptic lability showed that significant native structure in the cystine loop is preserved in the absence of covalent bonding between residues 93 and 110. Since no correlation was observed between the behaviour of these mutants with regard to toxin stability, emesis and T cell proliferation, we conclude that SEC1 -induced emesis and T cell proliferation are dependent on separate regions of the molecule. The disulphide bond itself is not an absolute requirement for either activity. However, conformation within or adjacent to the loop is important for emesis. Although mutants with alanine substitutions were not emetic, those with serine substitutions retained this activity, suggesting that the disulphide linkage stabilizes a crucial conformation but can be replaced by residues which hydrogen bond.