Aβ as a bioflocculant: implications for the amyloid hypothesis of Alzheimer’s disease

Research into Alzheimer’s disease (AD) has been guided by the view that deposits of fibrillar amyloid-β peptide (Aβ) are neurotoxic and are largely responsible for the neurodegeneration that accompanies the disease. This ‘amyloid hypothesis’ has claimed support from a wide range of molecular, genetic and animal studies. We critically review these observations and highlight inconsistencies between the predictions of the amyloid hypothesis and the published data. We show that the data provide equal support for a ‘bioflocculant hypothesis’, which posits that Aβ is normally produced to bind neurotoxic solutes (such as metal ions), while the precipitation of Aβ into plaques may be an efficient means of presenting these toxins to phagocytes. We conclude that if the deposition of Aβ represents a physiological response to injury then therapeutic treatments aimed at reducing the availability of Aβ may hasten the disease process and associated cognitive decline in AD.     

sIL－2R与SLE的临床表现和自身抗体的相关性

用双抗体夹心ＥＬＩＳＡ检测６６例ＳＩＥ病人血清叽ｓＩＬ－２Ｒ水平，ＳＬＥ病人显著高于正常人，疾病活动期高于非活动期。血清ｓＩＬ－２Ｒ水平与ＡＮＡ、抗ｄｓ－ＤＮＡ抗体、抗Ｓｍ、ＳＳ－Ａ、ＳＳ－Ｂ抗体无关，而与ＳＬＥ患者的发热、贫血、白细胞减少、关节受累及肾脏损害相关，且与ＳＬＥ疾病活动性和ＥＳＲ成正相关，与补体Ｃ＿３、Ｃ＿４和ＣＨ＿（５０）成负相关。提示血清ｓＩＬ－２Ｒ水平是监测ＳＬＥ疾病活动性的一个良好指标。     

Effects of 17 beta-oestradiol on function of lymphocytes from normal donors and patients with common variable immunodeficiency (CVID).

Effects of oestradiol (E2) have been studied on the in vitro T cell-dependent differentiation of B cells from peripheral blood and spleen using normal donors and patients with the antibody deficiency disease CVID. We also studied whether it modifies T cell DNA synthesis. The effect of E2 was examined on cultures of B cells with T cells for IL-2-driven immunoglobulin secretion or of T cells for phytohaemagglutinin (PHA)-driven DNA synthesis. Interestingly, in control experiments without E2, the normal sex difference in immunoglobulin production is reversed in CVID. The data show that for normal individuals there is no major difference between male and female donors in the in vitro actions of E2 on blood B and T lymphocytes. With normal blood B cells, E2 failed to affect IgM production, but it did inhibit IgG. In normal splenic cells, E2 increased both IgM and IgG secretion in a similar way to the tonsillar cell data previously reported. E2 on normal blood T cell DNA synthesis was stimulatory. With blood cells from CVID patients an interesting contrast was seen. As with normal B cells, E2 had no effect on IgM secretion by those CVID blood B cells able to secrete IgM. However, a difference between patients and normals was that E2 did not inhibit the IL-2-driven IgG production by those CVID B cells able to secrete IgG. For T cell function, the stimulatory effect of E2 on CVID T cell DNA was as in normal T cells. However, E2 failed to restore CVID B and T cell function to normal levels. These data suggest that there may be subtle defects in the pathway of action of E2 in CVID lymphocytes.     

Expression of TGFβ1/β3 during early chick embryo development

We have used an antibody against a TGFβ peptide fragment to localize this growth factor in the early chick embryo from laying to the ten-somite stage of development. Western blotting showed that the antibody reacted with both mammalian TGFβ1 and chicken TGFβ3. By immunocytochemistry we find that at the earliest developmental stage (stage X of Eyal-Giladi and Kochav) immunoreactivity to this antibody is primarily located in the cells of the area opaca and marginal zone, as well as in the most peripheral edge cells of the blastoderm. The yolk is non-reactive, except in a highly localized region subjacent to the edge cells. This pattern persists at stage XII, and at both stages individual isolated cells in the epiblast and hypoblast are also reactive. By the time to gastrulation, reactivity in the epiblast is polarized to the ventral extremity of the cells, and again some isolated cells in this layer are intensely immunoreactive. At this stage also, the endoderm cells, particularly those underlying the primitive streak, are positive, as are the mesoderm cells lateral to the streak. At somite stages, the neuroepithelium is not reactive but the ectoderm lateral to it is strongly positive. At the caudal primitive streak levels of early somite embryos, the ectoderm and endoderm are immunoreactive while the mesoderm loses the reactivity it showed at the early gastrulation stages. The neuroepithelial cells later show reactivity at their apical poles, and, as at the earlier stages, individual cells show intense labelling. These results indicate that TGFβ1 and/or TGFβ3 immunoreactivity is developmentally regulated from very early stages of morphogenesis in the chick, and together with data from earlier functional studies, suggest that this factor has roles in embryonic axis formation and in blastoderm expansion. © 1994 Wiley-Liss, Inc.     

Analysis of cytokine profiles in synovial T cell clones from chlamydial reactive arthritis patients: predominance of the Th1 subset.

Subpopulations of human T cells (Th0, Th1 and Th2) can be distinguished by their cytokine-secretion pattern. Evidence is increasing from other studies that the outcome of a human disease may depend on the subpopulation of T cells that predominates at the site of inflammation. Reactive arthritis serves as a useful model of chronic inflammatory diseases, because the triggering antigen can be identified. Using this triggering antigen we raised 33 T cell clones reactive with Chlamydia trachomatis and 25 T cell clones that were not reactive, all from the synovial fluid of two patients suffering from Chlamydia-induced arthritis. Their cytokine secretion patterns for interferon-gamma (IFN-gamma), IL-2 and IL-4 were analysed, as also were mRNAs for IFN-gamma and IL-10 by in situ hybridization. Out of the 33 antigen-reactive clones 23 showed a Th1 pattern with IFN-gamma but not IL-4 secretion, while the remaining 10 exhibited a Th0 pattern. The clones that did not react with Chlamydia expressed all patterns of cytokine secretion, including a Th2 pattern, thus providing a control population that excludes bias in the sampling procedure. CD4 and CD8 clones displayed a similar cytokine-secretion pattern. In addition this study demonstrates for the first time the expression of IL-10 mRNA in T cell clones derived from synovial fluid, and this was not confined to the Th2 subset. The Th1 response that Chlamydia provoke can be regarded as appropriate for such an obligate intracellular pathogen.     

Mechanics and Ca2+-sensitivity of human detrusor muscle bundles studied in vitro

Mechanical properties of isolated smooth muscle strips from human urinary bladder were investigated in vitro. Bladder tissue was obtained from tumour-free wall regions of bladders from male patients undergoing cystectomy for bladder carcinoma. In intact muscle strips, activated with high-K⁺ solution, half-maximal force occurred at about 0.9 mm extracellular [Ca²⁺]. The length-active force relation was determined and the muscle strips were fixed for light and electron microscopy at optimal length for active force (I_o). The maximal active force per unit smooth muscle cross-sectional area was 208±49 mN/mm², n= 6. Chemically skinned preparations were obtained by treatment with triton X-100. These preparations had a steep [Ca²⁺]-force relation in the micromolar range which was influenced by calmodulin. The skinned preparations could be maximally activated by irreversible thiophosphorylation of the regulatory light chains. The force-velocity relation was determined in the maximally activated skinned muscle at 22 °C at 0.5 1_o. When the muscle was shortened by 10%, force was reduced by 35% whereas the maximal shortening velocity was little affected.     

人肺癌细胞A549产生的免疫抑制因子对T细胞的作用及其生物学特性

本文系用人肺腺癌细胞株A549为研究对象,观察了TDSF对T淋巴细胞的作用,并对其某些生物学特性作了初步研究。实验表明:TDSF对T淋巴细胞的增殖、IL-2的产生及其反应性均有明显的抑制作用。TDSF作用相当强烈,这点是应用IL-2对肿瘤进行免疫治疗时应该注意的问题。丝裂霉素等抗代谢药物可抑制TDSF的分泌,提示TDSF为瘤细胞合成和分泌的基因产物。TDSF对酸、碱、热、胰蛋白酶敏感,分子量>150KD,表明其化学本质为蛋白质。     

Regulation of 5-hydroxytryptamine-induced calcium mobilization by cAMP-elevating agents in cultured canine tracheal smooth muscle cells

The effects of increases in cellular adenosine 3′5′-cyclic monophosphate (cAMP) on 5-hydroxytryptamine-(5-HT-) induced generation of inositol phosphates (IPs) and increases in intracellular Ca²⁺ ([Ca²⁺]_i) were investigated using canine cultured tracheal smooth muscle cells (TSMCs). Cholera toxin and forskolin induced concentration- and time-dependent cAMP formation with half-maximal effects (−logEC₅₀) produced at concentrations of 7.0 ± 0.5 and 4.9 ± 0.4  respectively. Pretreatment of TSMCs with either forskolin or dibutyryl cAMP inhibited 5-HT-stimulated responses. Even after treatment for 24h, these agents still inhibited the 5-HT-induced Ca²⁺ mobilization. The inhibitory effects of these agents produced both depression of the maximal response and a shift to the right of the concentration response curves of 5-HT. The water-soluble forskolin analogue L-858051 [7-deacetyl-7β-(γ-N-methylpiperazino)-butyryl forskolin] significantly inhibited the 5-HT-stimulated accumulation of IPs. In contrast, the addition of 1,9-dideoxy forskolin, an inactive forskolin analogue, had little effect on this response. Moreover, SQ-22536 [9-(tetrahydro-2-furanyl)-9-H-purin-6-amine], an inhibitor of adenylate cyclase, and both H-89 [N-(2-aminoethyl)-5-isoquinolinesulphonamide] and HA-1004[N-(2-guanidinoethyl)-5-isoquinolinesulphonamide], inhibitors of cAMP-dependent protein kinase (PKA), attenuated the ability of forskolin to inhibit the 5-HT-stimulated accumulation of IPs. These results suggest that activation of cAMP/PKA was involved in these inhibitory effects of forskolin. The AlF₄ ⁻-induced accumulation of IPs was inhibited by forskolin, suggesting that G protein(s) are directly activated by AlF₄ ⁻- and uncoupled from phospholipase C by forskolin treatment. These results suggest that activation of cAMP/PKA might inhibit the 5-HT-stimulated phosphoinositide breakdown and consequently reduce the [Ca²⁺]_i increase or inhibit both responses independently. Received: 14 March 1996/Accepted: 10 April 1996     

Anti-inflammatory activity of salmeterol: down-regulation of cytokine production.

Elevation of intracellular cAMP levels has been shown previously to inhibit cytokine secretion by various cell types in vitro. Since salmeterol is a beta 2-agonist which activates adenylate cyclase, its ability to inhibit cytokine production was evaluated. Though salmeterol, and the related drug albuterol, did not inhibit IL-1 beta production in vitro, both drugs did inhibit tumour necrosis factor-alpha (TNF-alpha) secretion by lipopolysaccharide (LPS)-activated THP-1 cells with similar IC50s of approximately 0.1 microM. This inhibition was effectively reversed by the beta 2-antagonist oxprenolol, indicating that the inhibition was mediated through the beta 2-adrenergic receptor. A strikingly different reactivity profile was seen with T cells. Salmeterol was able to inhibit the activation of both mouse and human T cells, as measured by proliferation and IL-2 secretion in response to anti-CD3 antibody, whereas albuterol was completely inactive in these assays. This T cell inhibition by salmeterol was about 10-fold less potent than that for TNF-alpha production, and was not reversed by a beta 2-antagonist, indicating that a different mechanism was involved in the effect of salmeterol on T cells. Paralleling the TNF-alpha inhibitory activity in vitro, oral dosing of salmeterol and albuterol inhibited LPS-induced increase in murine serum TNF level in vivo, with ED50s of approximately 0.1 mg/kg. This inhibition could be abrogated by dosing orally with the beta-blocker propranolol. The long-acting pharmacological profile of salmeterol was apparent in that it maintained its efficacy for 3 h, while albuterol had a much shorter duration of action. Salmeterol also had some protective effects in the galactosamine/LPS model of endotoxic shock, which is dependent upon TNF-alpha production. Though salmeterol inhibited serum TNF-alpha levels by up to 94% in this assay, it protected less than 50% of the animals from the lethal effects of the LPS/galactosamine mixture. This observation suggests that functional levels of TNF-alpha localized in tissues may not be accurately reflected by serum levels.     

Membrane carbohydrates of lymphoid cells: the receptor for interleukin 2

The contribution of sialic acids and of N-linked sugars to the biological activity of the receptor for IL 2 has been evaluated by treating activated cells with Neuraminidase or by growing them in the presence of inhibitors of N-linked glycosylation or processing. After treatment with Neuraminidase, Con A-activated spleen cells had not lost their ability to bind IL 2. The IL 2-absorbing capability was, however, strongly reduced after trypsinisation. 6 hours after Trypsin treatment, this property was again expressed. Proliferation of the IL 2-dependent CTLL cells was normal in the presence of Swainsonine but strongly impaired in the presence of Tunicamycin. Glycosylation of the IL 2 receptor may thus be required, but integrity of the sugars is not critical.