# Inhibitory NK receptor expression associates with altered antimalarial function of γδ T cells

## TL;DR

This study explores how inhibitory NK receptors on γδ T cells influence immune responses to malaria in children with high or low exposure.

## Contribution

The study identifies specific inhibitory NK receptors that modulate γδ T cell function in malaria-exposed children.

## Key findings

- NKG2A and KIR3DL1 expression correlates with enhanced γδ T cell responses to malaria antigens.
- KIR2DL1, KIR2DL2/3, and LILRB1 are associated with reduced γδ T cell activity and cytokine production.
- Inhibitory NK receptors regulate γδ T cell function in a finely tuned balance during malaria infection.

## Abstract

Gamma delta (γδ) T cells are important mediators of the immune response to childhood malaria. Human Vγ9+Vδ2+ T cells possess intrinsic, HLA-independent responsiveness to Plasmodium falciparum phosphoantigens produced in the blood stage of malaria. Engagement of the γδ T cell receptor (TCR) by phosphoantigen-bound butyrophilin molecules results in Vγ9+Vδ2+ T cell expansion, pro-inflammatory cytokine production, and release of cytotoxic granules that mediate parasite killing. Repeated P. falciparum infection, however, leads to a reduction in circulating Vγ9+Vδ2+ T cells and upregulation of immunomodulatory molecules, including NK receptors, that correlates with less severe symptoms upon infection. We explore phenotypic and functional differences of γδ T cells in Ugandan children with high versus low malaria exposure, utilizing high-parameter spectral flow cytometry analysis of PBMCs. We observed significant differences in expression of inhibitory NK receptors – KIR2DL1, KIR2DL2/3, KIR3DL1, LILRB1, and NKG2A – on γδ T cell subsets, with Vγ9+Vδ2+ T cells exhibiting a divergent mechanism of control compared to other subsets. We found that NKG2A and KIR3DL1 expression associated with potent Vγ9+Vδ2+ T cell responses to TCR- and Fc receptor (FcR)-mediated stimulation while KIR2DL1, KIR2DL2/3 and LILRB1 associated with reduced degranulation and cytokine production. These results identify a new role for inhibitory NK receptors expressed on γδ T cells, exerting a finely tuned balance of activating and inhibitory signals to regulate the response to malaria-related antigens.

Malaria remains one of the deadliest infectious diseases, disproportionately affecting young children in sub-Saharan Africa who succumb to sequelae of Plasmodium falciparum infection. However, children living in highly endemic areas experience repeated P. falciparum infection and develop naturally acquired–but not sterilizing–immunity which leads to an asymptomatic reinfection pattern. The immune factors that determine the balance of inflammatory and tolerogenic functions seen in non-sterilizing malaria immunity are yet to be fully understood. Here, we focus on the phenotypic and functional differences in one cell type between children with a history of low versus high malaria exposure. We identified a group of inhibitory surface receptors that improved the antimalarial function of this cell, and another group that worsened their function. Our study clarifies the immune landscape in highly malaria-exposed individuals and illuminates one potential system of regulating the cellular response to repeat infection.