Combinatorial Tim-3 and PD-1 activity sustains antigenspecific Th1 cell numbers during blood-stage malaria

Aims: Co-inhibitory receptors play a major role in controlling the Th1 response during blood-stage malaria. Whilst PD-1 is viewed as the dominant co-inhibitory receptor restricting T cell responses, the roles of other such receptors in coordinating Th1 cell activity during malaria are poorly understood.

Methods and Results: Here we show that the co-inhibitory receptor Tim-3 is expressed on splenic antigen-specific T-bet+ (Th1) OT-II cells transiently during the early stage of infection with transgenic Plasmodium yoelii NL parasites expressing ovalbumin (P. yoelii NL-OVA). We reveal that co-blockade of Tim-3 and PD-L1 during the acute phase of P. yoelii NL infection did not improve the Th1 cell response but instead led to a specific reduction in the numbers of splenic Th1 OT-II cells. Combined blockade of Tim-3 and PD-L1 did elevate anti-parasite IgG antibody responses. Nevertheless, coblockade of Tim-3 and PD-L1 did not affect IFN- production by OT-II cells and did not influence parasite control during P. yoelii NL-OVA infection.

Conclusion: Thus, our results show that Tim-3 plays an unexpected combinatorial role with PD-1 in promoting and / or sustaining a Th1 cell response during the early phase of blood-stage P. yoelii NL infection but combined blockade does not dramatically influence anti-parasite immunity.