Malaria-induced IL-10 contributes to the systemic burden of non-typhoidal Salmonella (164.10)

Non-typhoidal Salmonella serotypes (NTS) in pediatric patients with severe malaria can develop a life threatening bacteremia, a major source of child mortality in Sub-Saharan Africa. Here, we use a mouse model, mimicking severe anemia seen in humans, to address mechanisms by which an underlying malaria infection contributes to the increased risk of NTS bacteremia. Plasmodium yoelli infected red blood cells were administered i.p. in CBA or B6 mice. At peak parasitemia, Salmonella Typhimurium was administered by g.g. in a streptomycin-induced colitis model. Characterization of inflammation to NTS in the cecum was assessed by histopathology, microarray and qRT-PCR. Bacterial loads in systemic tissues were followed up to 4 days post inoculation. Our results indicate that the malaria parasite infection causes a global suppression of proinflammatory responses in the intestine, blunts intestinal neutrophil influx and increases the bacterial burden at systemic sites. Blunting of intestinal inflammatory responses was independent of antibody-induced anemia, but required induction of the immunoregulatory cytokine IL-10. Blocking IL-10 activity reduced systemic NTS in coinfected mice and administration of exogenous IL-10 was sufficient to increase the systemic burden of NTS in the absence of parasite infection. However, an increase in circulating NTS required both anemia and IL-10. Thus, we have identified two factors that synergize to increase bacteremia using a murine model.

Anti-inflammatory role of IL-10 producing macrophages during early Brucella abortus infection (117.20)

Chronic bacterial diseases such as Brucellosis may result from the pathogen’s ability to evade the initial immune response. Moreover, since Brucella spp. is known to target phagocytes, we investigated its effects on macrophage (mø) phenotype and induction of anti-inflammatory responses. Brucella did not induce alternative activation of mø in cultured bone marrow-derived mø (BMM) or in splenic CD11b+ cells isolated from mice during early infection. However, upregulation of interleukin 10 (IL-10) in serum, spleen and splenic mø from B. abortus infected mice was observed as early as 3 days post infection. Infection of BMM from MyD88-/-, TLR2-/-, TLR4-/-, TLR2/4-/- and TLR9-/- mice demonstrated that IL-10 induction was MyD88 dependent and was partially dependent on pathogen recognition by TLR2 and TLR4. Functionally, in vitro IL-10-/- BMM infection resulted in significantly higher pro-inflammatory cytokine production and decreased bacterial intracellular survival. In vivo 9 days infection of IL-10-/- mice confirmed a lower ability of B. abortus to survive in absence of IL-10, as well as higher induction of pro-inflammatory cytokines, resulting in increased pathology in liver and spleen of infected mice. Taken together, our results suggest that early IL-10 induction by infected mø contributes to an initial balance between pro-inflammatory and anti-inflammatory cytokines that is beneficial to the pathogen, thereby leading to enhanced bacterial survival and persistent infection.

IL-10 elicited during malaria infection blunts effective immune responses to non-typhoidal Salmonella (56.32)

Co-infection of non-typhoidal Salmonella serotypes (NTS) in pediatric patients with severe Plasmodium falciparum malaria can develop a life threatening bacteremia, a major source of child mortality in Africa. Here, we use a mouse model that mimics severe anemia seen in human malaria to address mechanisms by which an underlying malaria parasite infection contributes to the increased risk of developing NTS bacteremia. Plasmodium yoelli infected red blood cells were administered intraperitoneally in CBA, B6 or B6 il10-/- mice. At peak parasitemia, Salmonella Typhimurium was administered by gavage in a streptomycin-induced colitis model. Characterization of inflammation to NTS in the cecum was assessed by histopathology, microarray and qRT-PCR. Bacterial loads in systemic tissues were followed to 4 days post infection. Our results indicate that the malaria parasite infection causes a global suppression of proinflammatory responses in the intestine, blunts the intestinal neutrophil influx normally elicited during NTS gastroenteritis and increases bacterial colonization at systemic sites. Blunting of intestinal inflammatory responses was independent of hemolytic anemia, but required induction of the immunoregulatory cytokine IL-10 by the parasites. Elimination of IL-10 activity restored intestinal inflammation in co-infected mice, and administration of recombinant IL-10 was sufficient to increase systemic colonization by S. Typhimurium in the absence of parasite infection.

Amino acid replacements in the Serratia marcescens haemolysin ShIA define sites involved in activation and secretion

The haemolysin of Serratia marcescens (ShIA) is translocated through the cytoplasmic membrane by the signal peptide-dependent export apparatus. Translocation across the outer membrane (secretion) is mediated by the ShIB protein. Only the secreted form of ShIA is haemolytic. ShIB also converts in vitro inactive ShIA (ShIA*), synthesized in the absence of ShIB, into the haemolytic form (a process termed activation). To define regions in ShIA involved in both processes, ShIA derivatives were isolated and tested for secretion and activation. Analysis of C-terminally truncated proteins (ShIA) assigned the secretion signal to the amino-terminal 238 residues of ShIA. Trypsin cleavage of a secreted ShIA' derivative yielded a 15 kDa N-terminal fragment, by which a haemolytically inactive ShIA* protein could be activated in vitro. It is suggested that the haemolysin activation site is located in this N-terminal fragment. Replacement of asparagine-69 and asparagine-109 by isoleucine yielded inactive haemolysin derivatives. Both asparagine residues are part of two short sequence motifs, reading Ala-Asn-Pro-Asn, which are critical to both activation and secretion. These point mutants as well as N-terminal deletion derivatives which were not activated by ShIB were activated by adding a non-haemolytic N-terminal fragment synthesized in an ShIB+ strain (complementation). Apparently the activated N-terminal fragment substituted for the missing activation of the ShIA derivatives and directed them into the erythrocyte membrane, where they formed pores. It is concluded that activation is only required for initiation of pore formation, and that in vivo activation and secretion are tightly coupled processes. Complementation may also indicate that haemolysin oligomers form the pores.