Naïve CD8 T cell IFNγ responses to a vacuolar antigen are regulated by an inflammasome-independent NLRP3 pathway and Toxoplasma gondii ROP5

Abstract

Host resistance to Toxoplasma gondii relies on CD8 T cell IFNγ responses, which if modulated by the host or parasite could influence chronic infection and parasite transmission between hosts. Since host-parasite interactions that govern this response are not fully elucidated, we investigated requirements for eliciting naïve CD8 T cell IFNγ responses to a vacuolar resident antigen of T . gondii , TGD057. Naïve TGD057 antigen-specific CD8 T cells (T57) were isolated from transnuclear mice and responded to parasite-infected bone marrow-derived macrophages (BMDMs) in an antigen-dependent manner, first by producing IL-2 and then IFNγ. T57 IFNγ responses to TGD057 were independent of the parasite’s protein export machinery ASP5 and MYR1. Instead, host immunity pathways downstream of the regulatory Immunity-Related GTPases (IRG), including partial dependence on Guanylate-Binding Proteins, are required. Multiple T . gondii ROP5 isoforms and allele types, including ‘avirulent’ ROP5A from clade A and D parasite strains, were able to suppress CD8 T cell IFNγ responses to parasite-infected BMDMs. Phenotypic variance between clades B, C, D, F, and A strains suggest T57 IFNγ differentiation occurs independently of parasite virulence or any known IRG-ROP5 interaction. Consistent with this, removal of ROP5 is not enough to elicit maximal CD8 T cell IFNγ production to parasite-infected cells. Instead, macrophage expression of the pathogen sensors, NLRP3 and to a large extent NLRP1, were absolute requirements. Other members of the conventional inflammasome cascade are only partially required, as revealed by decreased but not abrogated T57 IFNγ responses to parasite-infected ASC, caspase-1/11, and gasdermin D deficient cells. Moreover, IFNγ production was only partially reduced in the absence of IL-12, IL-18 or IL-1R signaling. In summary, T . gondii effectors and host machinery that modulate parasitophorous vacuolar membranes, as well as NLR-dependent but inflammasome-independent pathways, determine the full commitment of CD8 T cells IFNγ responses to a vacuolar antigen.

Insight Into Inflammasome Signaling: Implications for Toxoplasma gondii Infection

“…However, the role of the inflammasome is dispensable and limited when TLR11 remains functional, due to TLR11-dependent IL-12 production is sufficient to generate Th1 immunity to the parasite without inflammasome dependent release of IL-18. Furthermore, Angel K. Kongsomboonvech et al recently reported that Naïve CD8 T cell IFN-g responses to T. gondii require the inflammasome-independent NLRP3 pathway and rhoptry proteins (ROP) 5 (59). This paper was identified that the NLRP3 regulates T cell function and underscore the need for NLRP3-activating adjuvants in vaccines targeted at inducing CD8 T cell-derived IFN-g responses to T. gondii.…”

“…Furthermore, Angel K. Kongsomboonvech et al. recently reported that Naïve CD8 T cell IFN-γ responses to T. gondii require the inflammasome-independent NLRP3 pathway and rhoptry proteins (ROP) 5 ( 59 ). This paper was identified that the NLRP3 regulates T cell function and underscore the need for NLRP3-activating adjuvants in vaccines targeted at inducing CD8 T cell-derived IFN-γ responses to T. gondii .…”

Genetic mapping reveals Nfkbid as a central regulator of humoral immunity to Toxoplasma gondii

“…Bone marrow derived macrophages (BMDMs) were generated as previously described [ 26 ], and plated on coverslips in 24 well plates in medium (4.5 g/liter D-glucose DMEM with GlutaMAX (Gibco), 10% heat-inactivated FBS, 1% penicillin-streptomycin (Gibco), 1X non-essential amino acids (Gibco, cat# 11140076), 1mM sodium pyruvate (Gibco, cat# 11360070)) supplemented with 10% L929 conditioned medium and incubated overnight 37°C, 5% CO 2 . Heat-inactivated blood plasma was used to coat live GFP+ parasites for 20 minutes at 37°C before infecting at a multiplicity of infection of 0.2.…”

“…“superinfect”) the brains of challenged survivors [ 25 ]. Vaccinated C57BL/6J mice are also susceptible to challenge with homologous strains, suggesting that defects in antigen recognition cannot fully explain immune failure to clear virulent strains [ 25 , 26 ]. During secondary infection memory CD8 T cells become exhausted, but checkpoint blockade fails to reverse disease outcome [ 27 ].…”

“…Fig 2. Genetic mapping revealsNfkbid is required for immunity to Toxoplasma gondii secondary infections 26. recombinant inbred (RI) mouse strains from the AxB;BxA panel were primed with 10 4 type III T. gondii CEP hxgprt-parasites; then, 35 days later, mice were challenged with 5x10 4 virulent type I GT1 T. gondii parasites (n = 2 per RI line).…”