Homolog of allograft inflammatory factor-1 induces macrophage migration during innate immune response in leech

Allograft inflammatory factor-1 (AIF-1) is a 17-kDa cytokine-inducible calcium-binding protein that, in vertebrates, plays an important role in the allograft immune response. Its expression is mostly limited to the monocyte/macrophage lineage. Until recently, AIF-1 was assumed to be a novel molecule involved in inflammatory responses. To clarify this aspect, we have investigated the expression of AIF-1 after bacterial challenge and its potential role in regulating the innate immune response in an invertebrate model, the medicinal leech ( Hirudo medicinalis ). Analysis of an expressed sequence tag library from the central nervous system of Hirudo revealed the presence of the gene Hmaif-1 /alias Hmiba1 , showing high homology with vertebrate aif-1 . Immunohistochemistry with an anti- Hm AIF-1 polyclonal antibody revealed the constitutive presence of this protein in spread CD68 + macrophage-like cells. A few hours after pathogen (bacterial) injection into the body wall, the amount of these immunopositive cells co-expressing Hm AIF-1 and the common leucocyte marker CD45 increased at the injected site. Moreover, the recombinant protein Hm AIF-1 induced massive angiogenesis and was a potent chemoattractant for macrophages. Following r Hm AIF-1 stimulation, macrophage-like cells co-expressed the macrophage marker CD68 and the surface glycoprotein CD45, which, in vertebrates, seems to have a role in the integrin-mediated adhesion of macrophages and in the regulation of the functional responsiveness of cells to chemoattractants. CD45 is therefore probably involved in leech macrophage-like cell activation and migration towards an inflammation site. We have also examined its potential effect on Hm AIF-1-induced signalling.