Stress-triggered signaling affecting survival or suicide of Streptococcus pneumoniae.

Streptococcus pneumoniae is a major human pathogen that can survive to stress conditions, such as the acidic environment of inflammatory foci, and tolerates lethal pH through a mechanism known as the acid tolerance response. We previously described that S. pneumoniae activates acidic-stress induced lysis in response to acidified environments, favoring the release of cell wall compounds, DNA and virulence factors. Here, we demonstrate that F(0)F(1)-ATPase is involved in the response to acidic stress. Chemical inhibitors (DCCD, optochin) of this proton pump repressed the ATR induction, but caused an increased ASIL. Confirming these findings, mutants of the subunit c of this enzyme showed the same phenotypes as inhibitors. Importantly, we demonstrated that F(0)F(1)-ATPase and ATR are necessary for the intracellular survival of the pneumococcus in macrophages. Alternatively, a screening of two-component system (TCS) mutants showed that ATR and survival in pneumocytes were controlled in contrasting ways by ComDE and CiaRH, which had been involved in the ASIL mechanism. Briefly, CiaRH was essential for ATR (ComE represses activation) whereas ComE was necessary for ASIL (CiaRH protects against induction). They did not regulate F0F1-ATPase expression, but control LytA expression on the pneumococcal surface. These results suggest that both TCSs and F(0)F(1)-ATPase control a stress response and decide between a survival or a suicide mechanism by independent pathways, either in vitro or in pneumocyte cultures. This biological model contributes to the current knowledge about bacterial response under stress conditions in host tissues, where pathogens need to survive in order to establish infections.

Passive transfer of Plasmodium falciparum MSP-2 pseudopeptide-induced antibodies efficiently controlled parasitemia in Plasmodium berghei-infected mice.

We have developed monoclonal antibodies directed against the pseudopeptide psi-130, derived from the highly conserved malarial antigen Plasmodium falciparum merozoite surface protein 2 (MSP-2), for obtaining novel molecular tools with potential applications in the control of malaria. Following isotype switching, these antibodies were tested for their ability to suppress blood-stage parasitemia through passive immunization in malaria-infected mice. Some proved totally effective in suppressing a lethal blood-stage challenge infection and others reduced malarial parasitemia. Protection against P. berghei malaria following Ig passive immunization can be associated with specific immunoglobulins induced by a site-directed designed MSP-2 reduced amide pseudopeptide.

Immunological profile of a Plasmodium vivax AMA-1 N-terminus peptide-carbon nanotube conjugate in an infected Plasmodium berghei mouse model.

We have covalently conjugated an N-terminus Plasmodium vivax apical membrane antigen-1 (AMA-1) peptide to functionalized carbon nanotubes (f-CNT). Immunological characterization of this molecular conjugate revealed that the immunogen-AMA-1 peptide was appropriately presented after being conjugated to CNTs as well as being recognized by BALB/c polyclonal antibodies. Subsequent experiments lead us to assess the AMA-1 peptide alone, as well as the CNT-peptide conjugate regarding rodent malarial infection. Remarkably, the peptide effectively controlled and delayed Plasmodium berghei-challenged animals' parasitaemia. The peptide-CNT conjugate displayed similar immunological properties to the peptide alone by protecting or delaying malarial infection. The peptide presentation by f-CNT to the immune system thus constitutes a promising approach for synthetic malarial vaccine formulation since the immunogen peptide conformation is well preserved.