The origin of lamellocytes in Drosophila melanogaster

摘要

Drosophila larvae defend themselves with a sophisticated cellular and humoral immune system, which shares similarities with the innate immune system of vertebrates. Therefore Drosophila became an excellent tool to study the innate immune reactions and host-parasite relationship (Hultmark 2003) in general. The cellular components of the Drosophila immune system are the hemocytes, they are present in three hemocyte compartments: in the circulation, in the lymph glands and attached to the cuticle, the latter are being the so called sessile hemocytes. In the larval circulation there are three differentiated cell types: plasmatocytes, lamellocytes and crystal cells. The majority (99%) of the hemocytes are plasmatocytes; they are responsible for phagocytosis of bacteria and apoptotic cells. The lamellocytes are large flattened cells, seldom seen prior to pupariation in wild type larvae. Upon parasitic wasp infestation the number of lamellocytes is dramatically increased in the circulation; their role is to eliminate foreign bodies and abnormally developing tissues by encapsulation (Rizki 1984). It is believed that following wasp infestation the lamellocytes originate from the lymph glands (Lanot et al. 2001; Sorrentino et al. 2002). Our preliminary data however suggested that this can not be the case.