Dendritic cell infection by Toxoplasma gondii: an intricate relationship

FACUNDO GARRIDO; SOFÍA DINAMARCA; FRANCO NIETO; NICOLAS BLANCHARD; LUIS S. MAYORGA; IGNACIO CEBRIÁN

Los Cocos, Córdoba

Congreso; XXXV Reunión Anual de la Sociedad Argentina de Protozoología; 2025

Sociedad Argentina de Protozoología

Dendritic cells (DCs) are the strongest antigen-presenting cells and unique linkers of innate and adaptive immunity. They present exogenous antigens associated with Major Histocompatibility Complex (MHC) Class II molecules through the classical pathway or with MHC-I molecules through the cross-presentation pathway to activate CD4+ or CD8+ T lymphocytes, respectively. Moreover, DCs represent one of the main cellular targets during infection by Toxoplasma gondii. This obligate intracellular parasite incorporates molecular components and essential nutrients from the host cell cytoplasm to grow and proliferate inside a highly specialized organelle, the parasitophorous vacuole (PV). While doing so, T. gondii modulates the host immune response through multiple interactions with proteins and lipids. In this study, we focus on the critical interactions between the PV and the host endoplasmic reticulum (ER), multivesicular bodies (MVBs) and the endocytic recycling compartment (ERC). We describe how these close interactions are relevant for the efficient transport of MHC-I molecules in DCs and parasite survival inside these cells.Particularly, we found that the ER resident SNARE protein Sec22b mediates the fusion of ERGIC-derived vesicles to the T. gondii PV. This ER-PV connection contributes to the optimal acquisition of the MHC-I peptide loading machinery and the subsequent presentation of parasite-derived antigens by DCs. To address the input of MBVs during this infectious process, we arrested MVBs biogenesis by using the inhibitor U18666A, a drug that interrupts cholesterol trafficking and changes the lipid composition of intracellular membranes. Upon DC treatment with U18666A, we evidenced a drastic disruption in the presentation of T. gondii-associated antigens and the parasite proliferation capacity. Since U18666A impairs the formation of MVBs, we analyzed the ESCRT machinery responsible for the generation of intraluminal vesicles in DCs infected by T. gondii. We observed that the main ESCRT-III component CHMP4b was massively recruited to the PV, and its expression level was upregulated upon DC infection by T. gondii. We demonstrated that U18666A treatment interrupted cholesterol delivery and CHMP4b recruitment to the PV, impacting significantly on parasite replication. Finally, to impair the ERC functionality during T. gondii infection, we silenced the expression of Rab22a in DCs. This experimental approach evidenced the contribution of MHC-I molecules from ERC vesicles to the PV, and drastically reduced the cross-presentation ability of T. gondii-associated antigens and the replicative capacity of the parasite.Altogether, our results highlight the importance of the ER-PV connection, MVBs formation and ERC integrity in DCs for efficient antigen presentation and T. gondii proliferation.