Immunology

Pattern Formation in Mosquitos

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Science  18 Aug 2006:
Vol. 313, Issue 5789, pp. 892-893
DOI: 10.1126/science.313.5789.892d

Like the innate immune systems of vertebrates, those of the insect world possess pattern recognition receptors that detect the broad signatures displayed by different classes of pathogens. In contrast, the narrow immune receptor specificity afforded by mechanisms of genetic recombination has been considered a feature unique to adaptive immunity in higher vertebrates. This view has recently undergone some revision, however, with the observation that lower vertebrates and invertebrates are also adept at manufacturing diverse immune receptors. For example, Drosophila use alternative splicing of transcripts from an immunoglobulin domain-containing locus—the Down syndrome cell adhesion molecule gene Dscam—to generate recognition receptors that assist in the phagocytosis of bacteria.

Dong et al. observe that in the mosquito Anopheles gambiae (the vector for malaria), the large number of exons in AgDscam could yield as many as 31,000 alternatively spliced products, a range similar to that calculated for Drosophila. Challenging mosquito cell lines with different pathogens resulted in a varied representation of these exons via alternative splicing and AgDscam molecules with distinct specificities. Evidence for alternative splicing of AgDscam was also demonstrated in adult mosquitos, and RNA interference-mediated silencing decreased the resistance of mosquitos to bacterial infection and to oocytes of the malaria parasite carried in the insect midgut. As in Drosophila, the AgDscam forms appeared to enhance phagocytosis of bacteria by hemocytes, although it is likely that the mechanism of Dscam action extends to other modes of immune defense. A further series of experiments revealed that the repertoires of AgDscam molecules could be tailored, in terms of binding affinity, to the infecting pathogens, underscoring the degree to which specificity provided by the Dscam system might help refine pathogen pattern recognition in insects. — SJS

PLoS Biol. 4, e229 (2006).

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