Thus, the latter antibody was categorised as weakly neutralising (Figure 5b)

Thus, the latter antibody was categorised as weakly neutralising (Figure 5b). == Figure 5. mapping == 1. Introduction == Streptococcus pneumoniae(pneumococcus) is the most common cause of bacterial otitis media, pneumonia, meningitis, sepsis and other severe illnesses [1]. This bacterium is the main etiological agent of severe pneumonia, causing up to 45% of pneumonia cases [2]. High morbidity and TES-1025 mortality related to pneumococcal infections demonstrate the need for novel treatment strategies. The currently available pneumococcal vaccines based on polysaccharide capsules can protect from about a quarter of knownS. pneumoniaeserotypes [3]. However, they do not protect from colonisation or infection by nonencapsulated pathogenic pneumococci [3,4]. Pneumolysin (PLY), a pore-forming toxin (PFT) produced by pneumococcus, is a Mouse monoclonal to SKP2 major protein virulence factor and a potential candidate for developing protein-based vaccines [5]. It is well-recognised that PLY plays a significant role in severe outcomes of pneumococcal disease, in particular in the pathogenesis of lung and myocardial dysfunction [6]. Development of pneumococcal disease leads to the dysfunction of the endothelial barrier, increasing its permeability and formation of pulmonary edema in the lungs. The edema formation correlates with the presence of PLY [7]. The pathogenic effects of PLY were also confirmed in animal models of pneumonia [8,9]. Therefore, strategies for neutralisation of the toxic activity of PLY might provide a tool for reducingS. pneumoniaepathogenicity. PLY belongs to the cholesterol-dependent cytolysin (CDC) family [10]. Oligomers of these toxins form large TES-1025 transmembrane pores consisting of 3050 monomers in the cholesterol-containing cell membranes [11,12]. The virulence of CDCs is mainly related to barrier dysfunction caused by cell attack. The crystallographic analysis of PLY protomers revealed characteristic structure consisting of four functional domains [13,14]. PLY monomer, like other CDCs, interacts with cholesterol-rich cell membrane through its domain 4 (D4) [13]. Prepore-forming PLY monomers assembled into oligomers on the cell membrane undergo critical structural changes in domain 3 (D3): alpha helical bundles (-HB1 and -HB2) transform into hairpins (TMH1 and TMH2) and perforate target membrane [15]. D4 is responsible for docking and anchoring of CDC to cholesterol in the cell membrane. The tip of D4 consists of four loops. The undecapeptide (UDP) loop is highly conserved among CDCs and forms an interaction site with membrane [16]. Moreover, the UDP is the element that couples membrane binding and allosteric changes in D3 leading to pore formation [17]. The cholesterol-recognition motive (CRM) of PLY composed of T459L460 pair located in the loop 1 (L1) [18]. Modulation of CDC binding properties is realised by the structure of loop 3 (L3) that allows the discrimination of the lipid environment of the membrane [18]. Besides pore formation, PLY has other ways of its pathogenic action on host cells. Recent data suggest that PLY at sublytic doses may TES-1025 allow pneumococci to TES-1025 invade alveolar macrophages and monocyte-derived dendritic cells by inhibiting proinflammatory cytokine responses, thus avoiding cell resistance to pneumococci [19]. The cytoskeleton rearrangement and proinflammatory responses could also be induced at sublytic doses of PLY [7,20,21,22,23]. Antibodies can be used directly for the elimination of CDC cytolytic or other harmful activity by blocking CDC binding to a cellular receptor or by interfering with CDC oligomerisation. The neutralising monoclonal antibodies (MAbs) were developed against several PFTs, including streptolysin O [24], TES-1025 listeriolysin O [25,26], vaginolysin [27] and PLY [28]. The neutralising MAb PLY-5 recognising the.