TG MIC1 AND TG MIC4 MICRONEMAL PROTEINS OF T.GONDII REGULATES PARASITE-INDUCED IL-12 PRODUCTION BY ANTIGEN PRESENTING CELLS

Camila Figueiredo Pinzan (FMRP); Elaine Vicente Lourenço (FMRP); Maria Cristina Roque Antunes Barreira (FMRP)

Introduction and Objectives: Microneme discharge is the first step in host invasion and the binding of micronemal proteins to host cells provides a molecular bridge to the parasite, thereby facilitating further steps of invasion. TgMIC1 and TgMIC4 are micronemes proteins that constitute a lactose-binding fraction (Lac+) purified from soluble tachyzoites antigen (STAg) of T. gondii. Host resistance to the intracellular protozoan Toxoplasma gondii is highly dependent on early IL-12 production by APC.Crude STAg was recently demonstrated as a potent inducer of IL-12 production by dendritic cells (DC), an activity presumably due to antigen interaction with TLR(s) on DC surface (Immunol Rev.201:26-34, 2004). Considering that the active STAg component(s) was not identified and lectins are potential ligands for TLRs, in this work, we evaluated if Lac+ fraction and MIC1 and MIC4 recombinant proteins can account for the IL-12 induction by different antigen presenting cells. Methods and Results: To examine if LAC+ induces IL-12 responsiveness in one or more cell types, highly enriched bone marrow-derived neutrophils, splenic dendritic cells and thioglycolate-elicited peritoneal macrophages were stimulated in vitro with 1g/ml of these proteins and IL-12p40 production was measured by ELISA. The LAC+ fraction induced high levels of IL-12 production by all cell types tested ( 972, 1790, 1100 pg/ml respectively). Moreover, the IL-12 production was significantly reduced by addition of of 0,05M lactose in cocultures showing that this characteristic was dependent on the lectin carbohydrate-recognition domain. These results suggest that IL-12 production is induced by TgMIC1 and TgMIC4 proteins that constitutes the LAC+ fraction. In order to unambiguously attribute this activity for these lectins we prepared both recombinant proteins. Our results showed that IL-12 responsiveness was also greatly induced in neutrophils, macrophages and dendritc cells stimulated in vitro with these recombinant micronemal proteins. Conclusion: Taken together, these data suggest that the micromemal lectins TgMIC1 and TgMIC4 from T. gondii induces APCs to release IL-12, a property that is possibly due to the TgMIC1/4/6 parasite complex in the nature. Financial support: FAPESP, FAEPA.