The immune response in insects and mammals : common origins

Insects have a highly efficient immune system. In response to a bacterial attack, their fat body (the equivalent of the liver in mammals) synthesizes a whole range of peptides with an antibacterial and antifungal effect. For several years now the "Immune response and development in insects" Laboratory (CNRS, Strasbourg) led by Jules Hoffmann, has been studying the mechanisms that control the antimicrobial response in insects, using the Drosophila as their model. Thanks to a genetic approach developed by Bruno Lemaitre, several different control pathways (or "cascades") governing the expression of the genes that code for antimicrobial peptides have been identified. This researcher showed that one of these cascades, the Toll pathway, is structurally and functionally similar to a specific pathway in mammals responsible for the expression of the genes involved in the acute phase immune response (1). This research demonstrates that the cascade involved in the immune response must have appeared early on in the evolution of eucaryotes. It also illustrates the striking similarities between the antimicrobial response in insects and the innate, nonadaptive response in mammals (2).

1. In mammals, the acute phase response refers to the changes in the bloodstream during primary response to infection. In this response, the blood cells and liver produce a whole range of proteins.
2. A mammal's primary response to infection depends on innate immunity, which is based on a variety of mechanisms that recognize and respond to the presence of a pathogen (including, among other things, the acute phase response). This response is followed by the adaptive response mediated through clonal selection of specific lymphocytes, which provides long-term protection against a given pathogen.

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