The early human interferon gamma response to Toxoplasma gondii is driven by Vγ9Vδ2 T-cell sensing of host phosphoantigens and subsequent NK-cell activation.

Toxoplasma gondii is a globally prevalent intracellular parasite that infects ~40 million Americans. The murine immune response to Toxoplasma relies on both toll-like receptor (TLR) 11/12 and immunity related GTPase-mediated (IRGs) responses, which humans lack, making it unclear how the human immune response detects and responds to the parasite. We investigated whether human Vγ9Vδ2 T cells, which detect phosphoantigens through the BTN3A1 receptor, shape the early immune response to the parasite. Using primary human peripheral blood mononuclear cells (PBMCs), we show that Vγ9Vδ2 T cells are activated by Toxoplasma-infected cells in a BTN3A1-dependent manner leading to secretion of interferon gamma (IFNγ) and tumor necrosis factor-alpha (TNFα). Additionally, these T cells potentiate IFNγ production by natural killer (NK) cells, likely via TNFα and interleukin (IL)-12 produced during infection. Active parasite invasion is required to stimulate the IFNγ response, and inhibition of the host mevalonate pathway, which limits the synthesis of the phosphoantigen isopentenyl pyrophosphate (IPP), attenuates the cytokine response, indicating Toxoplasma infection increases host phosphoantigens leading to Vγ9Vδ2 T cell activation. Our findings identify Vγ9Vδ2 T cells as key effectors that potentiate NK cells in the early human immune response to Toxoplasma, bridging innate and adaptive immunity in the absence of TLR11/12 signaling.