title: Overloading the immunity of the mosquito Anopheles gambiae with multiple immune challenges.
abstract: BACKGROUND
  Melanisation - the production and deposition of a layer of melanin that encapsulates many pathogens, including bacteria, filarial nematodes and malaria parasites is one of the main immune responses in mosquitoes. Can a high parasite load overload this immune response? If so, how is the melanisation response distributed among the individual parasites?
  
  
  METHODS
  We considered these questions with the mosquito Anopheles gambiae by inoculating individuals simultaneously with one, two or three negatively charged Sephadex beads, and estimating the melanisation as the darkness of the bead (which ranges from about 0 for unmelanised beads to 100 for the most melanised beads of our experiment).
  
  
  RESULTS
  As the number of beads increased, the average degree to which beads were melanised decreased from 71 to 50. While the darkness of the least melanised bead in a mosquito decreased from an average of 71 to 35, the darkness of the most strongly melanised one did not change with the number of beads.
  
  
  CONCLUSIONS
  As the number of beads increased, the mosquito's immune response became overloaded. The mosquito's response was to prioritise the melanisation of one bead rather than distributing its response over all beads. Such immune overloading may be an important factor underlying the evolution of resistance against vector-borne diseases.
authors.affiliation: Laboratory of Ecology and Epidemiology of Parasites, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland. antoine.barreaux@gmail.com.
authors.forename: A M G
authors.initials: AM
authors.lastname: Barreaux
authors.affiliation: Laboratory of Ecology and Epidemiology of Parasites, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Barreaux
authors.affiliation: Laboratory of Ecology and Epidemiology of Parasites, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland.
authors.forename: J C
authors.initials: JC
authors.lastname: Koella
mesh_terms: D000818:Animals; D000852:Anopheles / Q000276:immunology*; D003116:Color; D007303:Insect Vectors / Q000276:immunology*; D008543:Melanins / Q000276:immunology
chemical_list: D008543:Melanins
keywords: Anopheles gambiae; Immune overloading; Insect immunity; Melanisation; Mosquito