Insect immunity may display hitherto unsuspected molecular complexity. Researchers at Harvard Medical School in Boston investigated whether Dscam – a gene made famous by its prolific alternative splicing – plays a role in immune response. "The number of immune receptors might go from a couple of dozen up to thousands in insects," says study coauthor Dietmar Schmucker.
Using reverse transcriptase polymerase chain reaction, the investigators found the immunoglobulin superfamily receptor expressed in Drosophila hemocytes, which are involved in phagocytosis, and other immune-related cells. Microarray analysis for alternatively spliced Dscam exons suggested that immune cells could generate more than 18,000 receptor isoforms. "This diversity of proteins certainly raises the parallel to antibodies in higher mammals," says Brenton Graveley at the University of Connecticut Health Center in Farmington.
The researchers found that some Dscam isoforms could bind Escherichia coli, while others could not, suggesting that the insects possess a type of adaptive immunity that evolved parallel to mammalian immunity. Gravely notes that the Ig structures and mechanisms for diversification are different between fly and mammal. Moreover, the mammalian Dscam homolog "is not alternatively spliced to an appreciable extent." Schmucker, whose group discovered the alternative-splicing proclivity of Dscam in Drosophila, says that levels of insect and mammalian immune molecular diversity may reflect their different lifestyles. "Insects live only a few months, some a few years, so that makes a big impact in how you invest in immunity."