Inability to form new memories is an early clinical sign of Alzheimer’s disease (AD). There is ample evidence that the amyloid-β (Aβ) peptide plays a key role in the pathogenesis of this disorder. Soluble, bio-derived oligomers of Aβ are proposed as the key mediators of synaptic and cognitive dysfunction, but more tractable models of Aβ−mediated cognitive impairment are needed. Here we report that, in mice, acute intracerebroventricular injections of synthetic Aβ _1–42 oligomers impaired consolidation of the long-term recognition memory, whereas mature Aβ _1–42 fibrils and freshly dissolved peptide did not. The deficit induced by oligomers was reversible and was prevented by an anti-Aβ antibody. It has been suggested that the cellular prion protein (PrP ^C ) mediates the impairment of synaptic plasticity induced by Aβ. We confirmed that Aβ _1–42 oligomers interact with PrP ^C , with nanomolar affinity. However, PrP-expressing and PrP knock-out mice were equally susceptible to this impairment. These data suggest that Aβ _1–42 oligomers are responsible for cognitive impairment in AD and that PrP ^C is not required.

β-Amyloid precursor protein (APP) mutations cause familial Alzheimer's disease with nearly complete penetrance. We found an APP mutation [alanine-673→valine-673 (A673V)] that causes disease only in the homozygous state, whereas heterozygous carriers were unaffected, consistent with a recessive Mendelian trait of inheritance. The A673V mutation affected APP processing, resulting in enhanced β-amyloid (Aβ) production and formation of amyloid fibrils in vitro. Co-incubation of mutated and wild-type peptides conferred instability on Aβ aggregates and inhibited amyloidogenesis and neurotoxicity. The highly amyloidogenic effect of the A673V mutation in the homozygous state and its anti-amyloidogenic effect in the heterozygous state account for the autosomal recessive pattern of inheritance and have implications for genetic screening and the potential treatment of Alzheimer's disease.

Dendritic cells (DC) are migratory cells that exhibit complex trafficking properties in vivo. The present study was designed to characterize receptor expression and responsiveness to chemoattractants of human DC obtained from PBMC by culture with granulocyte/macrophage-CSF and IL-13. DC expressed appreciable levels of the CCR1, CCR2, and CCR5 receptors for the CC chemokines and the chemokine receptors CXCR1, CXCR2, and CXCR4. DC increased intracellular free calcium and migrated in response to the CC chemokines MCP-3, MCP-4, RANTES, MIP-1alpha, MIP-1beta, and MIP-5/HCC2 and the CXC chemokine SDF-1. In contrast, the CC chemokines MCP-1 and eotaxin had little or no activity in the concentration range tested (up to 1 microg/ml). IL-8 and Gro-beta (CXC) and lymphotactin (C chemokines) were also inactive. DC did not respond to 5-HETE, whereas platelet-activating factor was an active agonist. Selected chemokines active on DC in terms of migration and calcium fluxes were examined for their capacity to modulate endocytosis and Ag presentation. Under conditions in which TNF-alpha was active, MCP-1, MCP-3, MIP-1alpha, and RANTES did not affect these two responses. Thus, among hemopoietic elements, DC respond to a unique set of CC and CXC chemokines, and their responsiveness is restricted to migration with no effect on Ag capture and presentation. Chemokines may play a role in the trafficking of DC under resting or stimulated conditions. Chemokine receptors expressed in DC are likely to underlie HIV infection of this cell type.

Shiga toxin (Stx)-producing E.coli O157:H7 has become a global threat to public health; it is a primary cause of diarrhea-associated hemolytic uremic syndrome (HUS), a disorder of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure with thrombi occluding renal microcirculation. In this study, we explored whether Stx triggers complement-dependent microvascular thrombosis in in vitro and in vivo experimental settings of HUS. Stx induced on human microvascular endothelial cell surface the expression of P-selectin, which bound and activated C3 via the alternative pathway, leading to thrombus formation under flow. In the search for mechanisms linking complement activation and thrombosis, we found that exuberant complement activation in response to Stx generated an increased amount of C3a that caused further endothelial P-selectin expression, thrombomodulin (TM) loss, and thrombus formation. In a murine model of HUS obtained by coinjection of Stx2 and LPS and characterized by thrombocytopenia and renal dysfunction, upregulation of glomerular endothelial P-selectin was associated with C3 and fibrin(ogen) deposits, platelet clumps, and reduced TM expression. Treatment with anti–P-selectin Ab limited glomerular C3 accumulation. Factor B-deficient mice after Stx2/LPS exhibited less thrombocytopenia and were protected against glomerular abnormalities and renal function impairment, indicating the involvement of complement activation via the alternative pathway in the glomerular thrombotic process in HUS mice. The functional role of C3a was documented by data showing that glomerular fibrin(ogen), platelet clumps, and TM loss were markedly decreased in HUS mice receiving C3aR antagonist. These results identify Stx-induced complement activation, via P-selectin, as a key mechanism of C3a-dependent microvascular thrombosis in diarrhea-associated HUS.