They further revealed that human ADA2 promotes CD4+ T cell-dependent differentiation of monocytes to macrophages and their subsequent proliferation and that this role of ADA2 is independent of its ADA catalytic function. ADA2 belongs to the family of ADGF proteins, first characterized in insect. The ADGF-A protein from Drosophila melanogaster is similar to secreted human ADA2 and both proteins share all structure domains, including those considered unique to ADA2. However, ADGF-A, as with other ADGFs from lower species, has a higher affinity for adenosine than human ADA2. According to Zavialov et al., human ADA2 may have become specialized during evolution to be an adenosine deaminase EX 527 specifically active in sites of high adenosine concentration and lower pH, typified by sites of inflammation. We have showed that ADGF-A mRNA is expressed in the Drosophila hematopoietic organ, called the lymph gland and that this expression is required for larval survival. Drosophila hematopoiesis and cellular immunity are much simpler than in vertebrates, nevertheless both systems share many features. The main component of cellular immunity in flies is represented by plasmatocytes that are macrophage-like cells with phagocytic activity. These cells are responsible for the inflammatory response to tissue damage and infection. In similarity to vertebrate systems, these macrophagelike cells are attracted to sites of injury where they adhere and become phagocytic. This ability to recognize and adhere to damaged or “nonself�?tissue is an ancestral feature of blood cells. In the case of larger objects, such as parasitic wasp eggs, specialized cells called lamellocytes differentiate from prohemocytes and encapsulate the foreign object, thus isolating it from the rest of the body cavity. The intruding object is then destroyed by melanization; an important immune mechanism in arthropods utilizing toxic quinone substances and other shortlived reaction intermediates. These substances are also involved in the formation of more long-lasting products such as the melanin that physically encapsulates pathogens. Furthermore, reaction intermediates in the melanin pathway participate in the wound healing process by the formation of covalent links in damaged tissues and results in sclerotization. Since hemocyte ADGF-A mRNA expression is required for larval survival, we were interested in the regulation of its expression. However, because there is no available antibody against ADGF-A, we decided to produce a vital GFP reporter for its expression using homologous recombination. Here we show that this reporter is expressed in vivo, in aggregating larval hemocytes at sites of inflammation and that the acute expression of the ADGF-A protein is most probably regulated at posttranscriptional level. The adenosine deaminase activity of ADGF-A is an important regulator of extra-cellular adenosine in Drosophila larvae.