. Alzheimer disease macrophages shuttle amyloid-beta from neurons to vessels, contributing to amyloid angiopathy. Acta Neuropathol. 2009 Feb;117(2):111-24. PubMed.

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  1. This paper describes a mechanism by which macrophages may participate in the development of congophilic amyloid angiopathy. The results are consistent with Aβ-engorged macrophages being unable to transit across the endothelial cell barrier, ultimately succumbing to toxic actions of extracellular Aβ, and disgorging their contents near the vessels. Such a mechanism may explain why anti-Aβ antibodies promote congophilic angiopathy, which by itself may increase the risk of microhemorrhage, as observed with immunotherapy (Pfeifer et al., 2003; Wilcock et al., 2004; Racke et al., 2005; Schroeder et al., 2008; Boche et al., 2008). The mechanisms may also explain why antibodies which do not facilitate macrophage phagocytosis, via Fc receptor interactions, may minimize these potentially adverse consequences (Wilcock et al., 2006).

    References:

    . Deglycosylated anti-amyloid-beta antibodies eliminate cognitive deficits and reduce parenchymal amyloid with minimal vascular consequences in aged amyloid precursor protein transgenic mice. J Neurosci. 2006 May 17;26(20):5340-6. PubMed.

    . Passive immunotherapy against Abeta in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage. J Neuroinflammation. 2004 Dec 8;1(1):24. PubMed.

    . Cerebral hemorrhage after passive anti-Abeta immunotherapy. Science. 2002 Nov 15;298(5597):1379. PubMed.

    . Exacerbation of cerebral amyloid angiopathy-associated microhemorrhage in amyloid precursor protein transgenic mice by immunotherapy is dependent on antibody recognition of deposited forms of amyloid beta. J Neurosci. 2005 Jan 19;25(3):629-36. PubMed.

    . Immunotherapy reduces vascular amyloid-beta in PDAPP mice. J Neurosci. 2008 Jul 2;28(27):6787-93. PubMed.

    . Consequence of Abeta immunization on the vasculature of human Alzheimer's disease brain. Brain. 2008 Dec;131(Pt 12):3299-310. PubMed.

  2. We thank Dr. Morgan for his comment. We do believe that deficient innate immune clearance of amyloid-β plays an important role in Alzheimer disease that is often overlooked in this field. Our laboratory is investigating potential targeted therapeutics that may alleviate some of the immunological deficiencies of AD patients. For example, we chose to study curcuminoids (from Indian curry root) because of the lower occurrence of AD in India, where curry is a staple of the country’s cuisine (4). Our in-vitro studies provide evidence that curcuminoids could play an important role in treating innate immune deficiencies, including amyloid-β phagocytosis as well as TLR and MGAT-3 expression (1,6).

    We most recently directed our attention to vitamin D, and found that in vitro it significantly enhances amyloid-β phagocytosis in AD macrophages and also plays an anti-apoptotic role (2). These results are encouraging, especially in light of clinical data suggesting that vitamin D levels in blood serum of Alzheimer patients are significantly lower than control subjects (3,5). It can be argued that Alzheimer disease patients have lower blood serum vitamin D levels because they are less active than the general population and consequently have less exposure to sunlight. Nevertheless, we have data to suggest that increased vitamin D levels can enhance the innate immune function of AD patients. These results have been prepared in a manuscript which was accepted for publication by the Journal of Alzheimer’s Disease.

    Finally, Dr. Morgan's explanation concerning anti-Aβ antibodies promoting congophilic angiopathy is insightful. We commend Dr. Morgan on his group's discovery that deglycosylating IgGs is one way to decrease Aβ in the brains of APP-transgenic mice without the adverse vascular effects of unmodified anti-Aβ antibodies.

    References:

    . Innate immunity and transcription of MGAT-III and Toll-like receptors in Alzheimer's disease patients are improved by bisdemethoxycurcumin. Proc Natl Acad Sci U S A. 2007 Jul 31;104(31):12849-54. PubMed.

    . 1alpha,25-dihydroxyvitamin D3 interacts with curcuminoids to stimulate amyloid-beta clearance by macrophages of Alzheimer's disease patients. J Alzheimers Dis. 2009;17(3):703-17. PubMed.

    . Is vitamin D important for preserving cognition? A positive correlation of serum 25-hydroxyvitamin D concentration with cognitive function. Arch Biochem Biophys. 2007 Apr 15;460(2):202-5. PubMed.

    . A potential role of the curry spice curcumin in Alzheimer's disease. Curr Alzheimer Res. 2005 Apr;2(2):131-6. PubMed.

    . Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. Am J Geriatr Psychiatry. 2006 Dec;14(12):1032-40. PubMed.

    . Curcuminoids enhance amyloid-beta uptake by macrophages of Alzheimer's disease patients. J Alzheimers Dis. 2006 Sep;10(1):1-7. PubMed.