The human recombinant RNASET2 activates the initial phase of the inflammatory response in the medicinal leech

Recent studies have demonstrated that RNASET2, the only member of the ribonuclease T2 family present in human genome, is involved in the control of tumorigenicity in ovarian cancer cells. Furthermore its capacity to be a chemoattractant for numerous cells of monocytic-macrophage line and the possibility to act as an inducer of the innate immune response in Vertebrates have been established. In fact, in tumor tissues the detectable cross-talk between cancer cells and the surrounding tumor microenvironment is based on these aspects. Although several studies have been reported on the molecular features of RNASET2, the details on the pathways by which this evolutionarily conserved protein regulates the immune system are still poorly defined. In order to better elucidate these aspects, we report here the effect of the human recombinant RNASET2 injection and its role in regulating the innate immune response after bacterial challenge in an invertebrate model, the medicinal leech. This animal has been chosen for its very simple anatomy and for its rapid inflammatory response. Indeed, after few hours from the injection, a large number of fibroblasts are visible in the connective tissue that appears completely remolded and infiltrated by numerous cells expressing the specifics macrophage markers CD68 and HmAIF1. In order to confirm the ability of this ribonuclease to attract macrophages, we used a consolidated experimental approach based on the injection in the leech body wall of the Matrigel biomatrice (MG), supplemented with the human recombinant RNASET2. After one week, the extracted MG sponges was infiltrated by numerous cells CD68+ and HmAIF1+. Moreover, in the leech body wall challenged with lipopolysaccharides (LPS) or with the environmental bacteria pathogen Micrococcus nishinomiyaensis, endogenous RNASET2 is highly expressed by the numerous macrophages migrating to the site of inoculation. Taken together, these results clearly suggest that RNASET2 is likely involved in the initial phase of the inflammatory response in leeches.