Drosophila Hemopoiesis and Cellular Immunity

Abstract

In Drosophila melanogaster larvae, three classes of circulating cellular immune surveillance cells (hemocytes) can be identified: plasmatocytes, crystal cells, and lamellocytes. Plasmatocytes are professional phagocytes most similar to the mammalian monocyte/macrophage lineage and make up ∼95% of circulating hemocytes. The other ∼5% of circulating hemocytes consists of crystal cells, which secrete components necessary for the melanization of invading organisms, as well as for wound repair. A third cell type known as lamellocytes are rarely seen in healthy larvae and are involved in the encapsulation of invading pathogens. There are no obvious mammalian counterparts for crystal cells or lamellocytes, and there is no equivalent to the lymphoid lineage in insects. In this review, I will discuss what is currently known about Drosophila hemopoiesis and the cellular immune response and where possible compare it to vertebrate mechanisms.

Senescence of the cellular immune response in Drosophila melanogaster

“…Finally we note that plasmatocyte haemocytes in adult Drosophila have closest similarity to the monocyte lineage that gives rise to macrophages in vertebrates [11]. Vertebrate macrophages have a plethora of roles including antibacterial defences, chemotaxis and wound repair but they specialise in phagocytosis; most of these functions decline with age in humans, mice and rats [51].…”

“…Phagocytosis is the main component of the Drosophila adult cellular immune response and is carried out by plasmatocytes [11]. Two other haemocyte classes are present in [4] Drosophila: lamellocytes encapsulate foreign objects (such as parasitoid eggs) and crystal cells store phenoloxidase for release following immune activation [12].…”

“…However, lamellocytes and crystal cells are found only in larvae [13], and are therefore not relevant to immune system ageing in adults. Drosophila haemocytes either circulate freely throughout the haemolymph or are sessile [11]. Phagocytosis is initiated by binding of pathogen recognition receptors such as Eater [14] and PGRP-LC [15], and may be mediated by opsonin molecules that target microbes for engulfment [10].…”

Structural and functional characterization of pseudopodocyte, a shaggy immune cell produced by two Drosophila species of the obscura group

“…These blood cells are involved in a variety of innate immune defense reactions such as phagocytosis, nodulation, wound repair, coagulation, cytotoxicity, production of antimicrobial peptides, and encapsulation of large foreign bodies (Lanot et al, 2001;Tzou et al, 2002;Galko and Krasnow, 2004;Meister, 2004;Nappi and Christensen, 2005;Russo et al, 1996;Williams, 2007).…”

“…They derive from stem cells (the prohemocytes) through specific lineages of differentiation in the hematopoietic organ (the so-called lymph gland) (Lanot et al, 2001;Williams, 2007) or from subepidermal sessile hemocytes (Márkus et al, 2009). The three types of circulating hemocytes exhibit different histological and cytological features and fulfill different roles regarding their participation in immune responses.…”