Of the many different antigens tested, the most effective appear to be bacterially derived components and in particular bacterial

toxins [1], [2] and [3]. Of those proteins studied to date, the highly homologous enterotoxins, cholera toxin (CT) from Vibrio cholerae and heat labile toxin from enterotoxigenic Escherichia coli (LT) have been shown to stimulate the most effective local and systemic anti-toxin responses. In addition, these proteins act as adjuvants, stimulating immune responses to normally non-immunogenic antigens that are admixed and simultaneously delivered to the mucosal surface [4] and [5]. Whilst the high toxicity of these proteins Perifosine in humans makes their use impractical for vaccine development, generation and testing of site-directed mutants has shown that proteins that lack toxicity can retain adjuvant activity [6]. These mutants have shown some success in human trials [7] but the admixed formulation of the vaccine may affect the efficiency of immune activation. Attempts to genetically fuse the proteins selleck screening library have had limited success [8]. This may reflect subtle changes to the assembly, structure and activity of the holotoxin caused when other proteins are linked to different regions of the toxin. Pneumolysin produced by S. pneumoniae is a 53-kDa

protein which is a member of the closely related thiol-activated haemolysins that use membrane cholesterol as the receptor for their cytolytic activities [9]. Whilst the toxin is generated as a monomer, the

protein can self-assemble to form ring shaped oligomer structures on cell membranes, which are believed to form the pores associated with pathogenesis. In fact, purified protein with mutations in particular regions known to affect oligomerisation are no longer toxic to red blood cells [10], [11] and [12]. In addition to its role in disease pneumolysin has been assigned several functions with respect to modification of the immune response. These include induction of inflammatory responses and modification of cell signalling [13]. The immunomodulatory activity of this protein 17-DMAG (Alvespimycin) HCl is not surprising given the fact that pneumolysin has recently been shown to bind to Toll-like receptor 4 (TLR-4) [14] and [15]; recognition of pathogen associated molecular patterns (PAMPs) through such receptors has been shown to results in changes in antigen presentation and cellular activation. In fact, failure to activate macrophages through TLR4 in transgenic knockout mice, makes these animals more susceptible to infection [15]. In addition, pneumolysin itself has been shown to provide some level of protection against bacterial challenge presumably by neutralisation of the cytotoxic and cytolytic activities of the toxin [10], [11] and [12]. Pneumolysin therefore plays a diverse and important role in the pathogenesis of pneumoccocal infections.