Modulation of bone marrow macrophage plasticity by gametocytes, the transmission stages of malaria parasite

Malaria is a parasitic disease causing 212 million cases and 429,000 deaths per year1. It mainly affects poor people in tropical developing countries, so that the perception of its impact is low in the so called “developed world”. This is especially sad in Italy, a country with both a millennial malaria history until eradication in the 1950’, and an excellent record of discoveries and research. This is one of the reasons why public engagement, to sensitize civil society to health and socio-economic problems of poor countries, is a special concern to the PI. A specific dissemination plan is proposed to increase people awareness about malaria and its consequences, through a bidirectional dialogue with the civil society. Malaria symptoms and fatal complications, mostly in children, are caused by the asexual cycle of Plasmodium protozoa, which complete the sexual cycle in the mosquito vector. Transmission from human to mosquito is due to the sexual forms called gametocytes (GCT), which appear in patients after cycles of asexual parasite growth. GCT develop in five stages (I-V): stages I-IV are retained in internal organs, mostly in the bone marrow (BM), whereas mature stage V GCT are found in the circulation even several days after a patient has been cured. This project aims at investigating a largely unknown, but important aspect of malaria transmission and GCT development: the molecular interplay between the GCT at different stages and the cells of innate immunity, the macrophages, both differentiating in the bone marrow. The idea of a possible interplay between GCT at different stages and macrophages emerged from preliminary data obtained by the PI together with Dr. Y Corbett, from the same group. The data suggest that stage V GCT induce in BMDM an inflammatory response, typical of the M1 phenotype. It is in fact reported that macrophages can be polarized by different stimuli towards different phenotypic profiles called M1 or M2 (macrophage plasticity or polarization). The main hypothesis is that the BM, due to the macrophage M1 responses, becomes a hostile microenvironment for mature GCT. Thus, they evade, escaping into circulation and ensuring transmission. Since young GCT, on the contrary, persist in the BM for the time necessary for their development, it is conceivable that they activate a different macrophage pathway (maybe M2) compared to mature GCT. The aims of the project are to: 1) Investigate whether young or mature GCT can induce BMDM polarization; 2) Investigate whether GCT can modulate the M1/M2 polarization induced by known stimuli; 3) Study if and how receptors of innate immunity are involved in the response of BMDM to GCT. The outcome will be a unique and novel database of immune responses against GCT in bone marrow, which will pave the way to the identification of new transmission blocking tool aimed to: a) Block the release of mature GCT from BM; b) Induce early release of immature GCT; c) Prevent the sequestration and/or development of GCT in the BM. The project will be organised in three work packages (WP), the objectives achieved through the realization of tasks (T) and verified by milestones. WP1 will study the induction and/or modulation of plasticity of BM derived macrophages (BMDM) by GCT at different stages of development (1-21 months). BMDM polarization induced by known stimuli will be evaluated by the expression of transcription factors, cytokines (CK)/chemokines and enzymes known to be specifically involved in M1 or M2 responses. GCT at different stages will be obtained as described by the PI4. BMDM will be stimulated with young or mature GCT and M1/M2 polarization will be discriminated for the espression of: i) M1/M2 transcription factors; ii) mRNA and proteins of a large number of CK and chemokines differentially involved in M1 or M2 maturation; iii) iNOS and arginase; iv) microRNA (miR) specifically involved in M1 (miR-155, miR-125, miR-2