Zedi, M. | bioRxiv Science

bioRxiv2025

CXCR6⁺ CD127- Tr1 Cells Balance Immunity and Persistence in Plasmodium falciparum Infection

Plasmodium falciparum (Pf) induces the clonal expansion of antigen-specific type 1 regulatory T (Tr1) cells with a capacity for long-term memory. Tr1 cells comprise nearly 90% of the Pf blood stage antigen-specific CD4+ T cell pool in children. Though, whether Tr1 cells contribute to protection from malaria remains undetermined. To address this critical gap in knowledge, we first performed scRNAseq on gated cell populations to validate CXCR6+ CD127- as new phenotypic markers to enrich for bona-fide Tr1 cells. Importantly, these Tr1 cells potently suppressed the proliferation of other CD4+ T cells in vitro via IL-10 secretion. Among children living in malaria-endemic Uganda, CXCR6+ CD127- Tr1 cells were the dominant responding subset to Pf-infected red blood cell stimulation in vitro. They also rapidly expanded following malaria and expressed IL-10 and IFNg during infection in vivo. Tr1 abundance correlated with plasma concentrations of granzyme A, IFNg, IL-10, and LAG3, suggesting that these cells act systemically. Higher CXCR6+ CD127- Tr1 cell frequencies correlated with a lower probability of symptoms given parasitemia but were also associated with delayed parasite clearance among untreated, asymptomatic children. These data suggest that Tr1 cells help mediate clinical immunity to malaria but may also facilitate parasite persistence through mechanisms of immune regulation.

immunology↗

bioRxiv2025

Significant variations in tolerance to clothianidin and pirimiphos-methyl in Anopheles gambiae and Anopheles funestus populations during a dramatic malaria resurgence despite sustained indoor residual spraying in Uganda

A dramatic malaria resurgence occurred in areas of Uganda between 2020 and 2022 coincident with the switch to clothianidin-based formulations for indoor residual spraying. During the resurgence, Anopheles funestus numbers increased but when an alternative insecticide, pirimiphos methyl, was reintroduced in 2023, both malaria cases and An. funestus mosquito density fell. In this study, we investigated possible causes of the resurgence by assessing; 1) whether sufficient quantities of insecticide were sprayed; 2) the residual insecticide bioefficacy against wild mosquitoes and; 3) the insecticide susceptibility of vector populations using standard test tube assays and wall cone assays. In 2023, after adjusting for extraction efficiency, 70-80% of the houses had optimal residual concentrations of insecticides (clothianidin >0.3g/m2; pirimiphos methyl >0.5g/m2) with significant variations between sampling rounds and wall types. Mud walls had the lowest residual concentration of insecticides, and the lowest observed mortality in wall cone assays, compared to fired bricks with plaster/cement/paint. In the studies of residual bio efficacy, by World Health Organization (WHO) definitions, An. funestus showed resistance to clothianidin (<80% mortality) up to 11 months and susceptibility to pirimiphos methyl (>90% mortality) when exposed to wall surfaces up to 7 months post-spray. In WHO tube tests, variations were observed in susceptibility to clothianidin in An. funestus populations using dose- and time-response assays (80-98% mortality). In 2022, An. gambiae was largely susceptible to the clothianidin-based formulation Sumishield (85-90% mortality) although the levels dropped slightly in 2023 (60-85% mortality) mainly in mud and pole houses. In contrast, An. gambiae was mildly susceptible to the pirimiphos methyl-based formulation Actellic ([~]80% mortality) and time response assays showed An. gambiae populations had very low knockdown and mortality at lower exposure time compared to An. funestus. Regression models showed a positive association between residual insecticide concentration (RIC) and mortality in houses sprayed with Sumishield but not Actellic houses. Despite the possible variations observed in spray operations, the study revealed that An. funestus exhibited a higher tolerance to clothianidin-based formulations compared to An. gambiae, and this might have driven the malaria resurgence observed in Uganda. However, there are signals of An. gambiae resistance to pirimiphos-methyl which will require further investigation and monitoring.

zoology↗