Inhibition by parasites of melanotic tumour formation in Drosophila melanogaster

Abstract

THE cellular defence mechanisms of insects are mediated by blood cells, or haemocytes, which eliminate invading foreign organisms by phagocytosis and encapsulation. The latter involves aggregation, adhesion and flattening of haemocytes around surfaces too large to be engulfed. This process is characteristically accompanied by the intra- and extracellular deposition of melanin^1–5. In larvae of Drosophila the reaction against internal metazoan parasites^6–8 is similar to the reaction which forms melanotic tumours in the body cavity of some mutant strains^9–14. In both cases haemocytes proliferate and differentiate prematurely. In some tumorous larvae the formation of these benign, inheritable masses represents an autoimmune response in which haemocytes encapsulate abnormal cells and tissues and form compact melanised masses¹¹.