Pathogen-produced catalase affects immune priming: A potential pathogen strategy.

Immune priming in invertebrates occurs when the first contact with a pathogen/parasite enhances resistance after a second encounter with the same strain or species. Although the mechanisms are not well understood, there is evidence that priming the immune response of some hosts leads to greater pro-oxidant production. Parasites, in turn, might counteract the host attack with antioxidants. Virulent pathogen strains may therefore mask invertebrate immune priming. For example, different parasite species overexpress catalase as a virulence factor to resist host pro-oxidants, possibly impairing the immune priming response. The aim of this study was firstly to evaluate the specificity of immune priming in Tenebrio molitor when facing homologous and heterologous challenges. Secondly, homologous challenges were carried out with two Metarhizium anisopliae strains (Ma10 and CAT). The more virulent strain (CAT) overexpresses catalase, an antioxidant that perhaps impairs a host immune response mediated by reactive oxygen species (ROS). Indeed, T. molitor larvae exhibited better immune priming (survival) in response to the Ma10 than CAT homologous challenge. Moreover, the administration of paraquat, an ROS-promoting agent, favoured survival of the host upon exposure to each fungal strain. We propose that some pathogens likely overcome pro-oxidant-mediated immune priming defences by producing antioxidants such as catalase.

Experimental inoculation of Artibeus jamaicensis bats with dengue virus serotypes 1 or 4 showed no evidence of sustained replication.

Dengue is the most important mosquito-borne viral disease to humans. Bats are potential reservoirs for flaviviruses, including dengue virus (DENV). In this work, Artibeus jamaicensis bats were inoculated with two serotypes of DENV using different routes. For experimental inoculations (EI) 1 and 2, bats were inoculated subcutaneously or intraperitoneally with DENV-4; for EI-3 bats were inoculated intraperitoneally with DENV-1. Mock inoculated bats were kept as controls. In EI-4, bats were bitten by Aedes aegypti mosquitoes infected with DENV-1 or 4. Reverse transcription-polymerase chain reaction assays in plasma and spleen tissue collected from Day 1 to Days 9-17 after inoculation failed to reveal the presence of viral RNA in any of the samples. No evidence of circulating NS1 or specific anti-DENV IgG was detected in the plasma of the inoculated bats. These results indicate that A. jamaicensis bats are incapable of sustaining dengue virus replication and are unlikely to act as reservoirs for this virus.

Diversity of Bacillus thuringiensis strains from Latin America with insecticidal activity against different mosquito species.

The characterization of selected Bacillus thuringiensis strains isolated from different Latin America countries is presented. Characterization was based on their insecticidal activity against Aedes aegypti, Culex quinquefasciatus, and Anopheles albimanus larvae, scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and plasmid profiles as well as PCR analysis using novel general and specific primers for cry and cyt genes encoding proteins active against mosquitoes (cyt1, cyt2, cry2, cry4A, cry4B, cry10, cry11, cry17, cry19, cry24, cry25, cry27, cry29, cry30, cry32, cry39, and cry40). Strains LBIT315, LBIT348, and IB604 showed threefold higher mosquitocidal activity against A. aegypti and C. quinquefasciatus larvae than B. thuringiensis subsp. israelensis and displayed high similarities with the B. thuringiensis subsp. israelensis used in this study with regard to protein and plasmid profiles and the presence of cry genes. Strain 147-8906 has activity against A. aegypti similar to that of B. thuringiensis subsp. israelensis but has different protein and plasmid profiles. This strain, harboring cry11, cry30, cyt1, and cyt2 genes, could be relevant for future resistance management interventions. Finally, the PCR screening strategy presented here led us to identify a putative novel cry11B gene.

Cellular-mediated reactions to foreign organisms inoculated into the hemocoel of Anopheles albimanus (Diptera: Culicidae).

The immune response against different organisms and particles inoculated in the hemocoel of female Anopheles albimanus Wiedemann was investigated. Histological and ultrastructural observations indicated that melanization and hemocyte type participation varied according to the particles inoculated. The initial responses against heat-killed Microccocus lysodeikticus and Escherichia coli included hemocyte lysis and melanization whereas the response to heat-killed Saccharomyces cerevisiae was only cellular, and an initial melanization of Sephadex G-25 (neutral charged) beads was followed by the formation of cellular aggregates. After 24 h, hemocytes were involved in all terminal encapsulation events. Plasmodium vivax Grassi and Feletti formalin-fixed sporozoites induced a weak response. Cellular aggregates were observed 1 h postinoculation, but participating hemocytes could not be identified because of the extensive cellular damage and lysis. Sporozoites were also observed in the core of these aggregates, mixed with cell debris and free in the hemolymph. The effect on the inoculated particles was also different-S. cerevisiae was encapsulated only by hemocytes, whereas M. lysodeikticus was lysed and E. coli was phagocytosed by plasmatocytes. These results indicate that hemocytes are important components in the immune response in An. albimanus.