pneumoniae /em were stained using a modified Thioflavin S protocol http://www-medlib.med.utah.edu/WebPath/webpath.html[46]. cortices of the AD brain with multiple em C. pneumoniae /em -specific antibodies. This immunoreactivity was seen in regions of amyloid deposition as revealed by immunolabeling with two different anti-beta amyloid antibodies. Thioflavin S staining, overlaid with em C. pneumoniae /em immunolabeling, demonstrated no direct co-localization of the organism and amyloid plaques. Further, the specificity of em C. pneumoniae /em labeling of AD brain sections was demonstrated using em C. pneumoniae /em antibodies pre-absorbed against amyloid 1-40 and 1-42 peptides. Conclusions Anti- em C. pneumoniae /em antibodies, obtained commercially, identified both typical intracellular and atypical extracellular em C. pneumoniae /em antigens in frontal and temporal cortices of the AD brain. em C. pneumoniae /em , amyloid deposits, and neurofibrillary tangles were present in the same regions of the brain in apposition to one another. Although additional studies are required to conclusively characterize the nature of Chlamydial immunoreactivity in the AD brain, these results further implicate em C. pneumoniae /em infection with the pathogenesis of Alzheimer’s disease. Background Alzheimer’s disease (AD) is a progressive neurological disease that affects millions of older individuals. Distinctive pathological hallmarks associated with the disease include tau accumulations forming neuropil threads (NTs) and neurofibrillary tangles (NFTs), and deposits of extracellular amyloid comprising neuritic senile plaques (NSPs). In general, there are two distinct forms of Alzheimer’s disease, familial AD and sporadic late-onset AD. The early onset form of the disease, known commonly as familial AD, is caused by dysregulation of many processes due to genetic mutations that lead to the aforementioned pathology. Rat monoclonal to CD4.The 4AM15 monoclonal reacts with the mouse CD4 molecule, a 55 kDa cell surface receptor. It is a member of the lg superfamily,primarily expressed on most thymocytes, a subset of T cells, and weakly on macrophages and dendritic cells. It acts as a coreceptor with the TCR during T cell activation and thymic differentiation by binding MHC classII and associating with the protein tyrosine kinase, lck For example, mutations in presenilins 1 and 2 genes and the gene responsible for amyloid- protein precursor (APP) result in an increased accumulation of beta-amyloid (A) in the brain. In late-onset sporadic AD, similar pathological accumulations occur, although without the gene mutations seen in familial AD (for review see Duyckaerts 2009) [1]. Most investigations have focused on the extracellular, deposited forms of amyloid in the AD brain. The Hexachlorophene extracellular accumulations of amyloid in the brain are composed principally of amyloid 1-40 and 1-42 and form neuritic senile plaques (NSP) [1,2]. However, intracellular accumulations of amyloid, which may occur prior to extracellular deposition, also have been demonstrated [3-6]. Further, A-derived diffusible ligands (ADDLs), soluble forms of amyloid, have been postulated to be a toxic form of amyloid at the synapses and are not found in typical neuropathological or histopathologic accumulations of amyloid [7]. Since late-onset AD lacks the same mutations seen in familial AD, determination of the cause of amyloid pathology in late-onset AD remains poorly understood. The interplay between normal processes and environmental factors, both independently and in concert with other genetic factors, may lead to late-onset AD. In particular, infections as environmental factors may have an impact on the delicate amyloid and tau balance in the brain and lead to the pathology Hexachlorophene seen in AD. A number of infectious agents have been associated with late-onset AD [8-12]. Our focus has been on the obligate, intracellular bacterium em Chlamydia pneumoniae /em , which has been demonstrated to be highly prevalent in the AD brain [8,12], as well as associated with other systemic and neurological diseases [13,14]including atherosclerosis [15,16], stroke [17], encephalitis [18], and multiple sclerosis [19]. Various cell types found in the brain have been shown to be susceptible to infection by em C. pneumoniae /em including endothelia, astroglia, microglia, and neurons [8,12,20-23]. Once inside the cell, em C. pneumoniae /em reside in an intracellular inclusion that resists lysosomal fusion and immune recognition. em C. pneumoniae /em developmentally cycle from the infectious elementary body (EBs) to the metabolically active reticulate body (RBs), which divide by binary fission. This obligate intracellular pathogen both interacts with and manipulates the host by gathering energy and nutrients that are required for replication, such as sphingomyelin and cholesterol [24-26]. Chlamydiae also inhibit apoptosis [20,27-29] and release factors such as chlamydial lipopolysaccharide (LPS) and glycolipid protein into both the cell itself and into the surrounding milieu [30]. Further propagation and spread of the organism may follow one or more pathways. The infectious progeny, EBs, may be released Hexachlorophene upon eventual cell death or by extrusion from the cell in a membrane bound package into the surrounding environment [31]. Thus, em C. pneumoniae /em and/or antigens derived from the organism may be localized both intracellularly and extracellularly at the site of infection. Due to the chronic nature of AD and the complexity of em C. pneumoniae Hexachlorophene /em infections, establishing an association with disease pathogenesis has proved difficult. Validating this association relies on a variety of detection methods for the organism. Our current study focuses on the use of immunohistochemistry (IHC) with a battery of commercially available anti-chlamydia antibodies on frontal and temporal cortical sections of.