Increased melanizing activity in Anopheles gambiae does not affect development of Plasmodium falciparum

Abstract

Serpins are central to the modulation of various innate immune responses in insects and are suspected to influence the outcome of malaria parasite infection in mosquito vectors. Three Anopheles gambiae serpins (SRPN1, -2, and -3) were tested for their ability to inhibit the prophenoloxidase cascade, a key regulatory process in the melanization response. Recombinant SRPN1 and -2 can bind and inhibit a heterologous phenoloxidase-activating protease and inhibit phenoloxidase activation in vitro. Using a reverse genetics approach, we studied the effect of SRPN2 on melanization in An. gambiae adult females in vivo. Depletion of SRPN2 from the mosquito hemolymph increases melanin deposition on foreign surfaces such as negatively charged Sephadex beads. As reported, the knockdown of SRPN2 adversely affects the ability of the rodent malaria parasite Plasmodium berghei to invade the midgut epithelium and develop into oocysts. Importantly, we tested whether the absence of SRPN2 from the hemolymph influences Plasmodium falciparum development. RNAi silencing of SRPN2 in an An. gambiae strain originally established from local populations in Yaoundé , Cameroon, did not influence the development of autochthonous field isolates of P. falciparum. This study suggests immune evasion strategies of the human malaria parasite and emphasizes the need to study mosquito innate immune responses toward the pathogens they transmit in natural vector-parasite combinations.innate immunity ͉ malaria ͉ mosquito ͉ serpin

Ecological Immunology of mosquito-malaria interactions: Of non-natural versus natural model systems and their inferences

“…Consequently, they too have repeatedly emphasized the limitations of non-natural modelsystems Dong et al 2006 ;Michel et al 2006). For example, Dong and colleagues (2006) in a comparison of An.…”

Analysis of Mutually Exclusive Alternatively Spliced Serpin-1 Isoforms and Identification of Serpin-1 Proteinase Complexes in Manduca sexta Hemolymph

“…A search of the raw MALDI-TOF peaks from trypsin-treated samples for predicted peptides from Lys 336 to the P1 residue for the remaining isoforms in putative complex bands (spots 16 -25) failed to reveal any additional isoform-specific information (data not shown). Of the four spots shown to contain HP8 by MS (spots 19,20,22,23), spot 19 contains serpin-1 isoform J based on PMF and MS/MS results. PMF results suggest that spots 19 and 20 contain serpin-1A, whereas spots 22 and 23 contain serpin-1E, but these identifications are more tentative because of the lack of MS/MS corroboration.…”

“…In insects, serine proteinase cascades initiated by microbial infection elicit antimicrobial peptide production and lead to activation of prophenoloxidase, which catalyzes the melanization response (5)(6)(7)(8)(9)(10)(11)(12)(13). Serpins inhibit proteinases required for prophenoloxidase activation in Manduca sexta (14 -17), Drosophila melanogaster (18 -21), Tenebrio molitor (22), and Anopheles gambiae (23). Serpins also regulate the Toll pathway in immune responses of D. melanogaster and T. molitor (22,24) and in D. melanogaster dorsal-ventral patterning (25,26).…”

Phenoloxidase Is an Important Component of the Defense against Aeromonas hydrophila Infection in a Crustacean, Pacifastacus leniusculus

“…Phenoloxidase has also been demonstrated to interfere with microbial infection in several insect species (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). In some cases melanization, or rather the activity of the enzyme PO, was found to have no or little impact on the killing/ clearance of parasites (24,25) and the melanization reaction was found not to be required for survival of mosquitoes/flies after certain microbial infections (26,27).…”