Biology subjects

Oyong, D.

Publications and source records attributed to Oyong, D..

5 recordsLinked to original sources

bioRxiv2026

Circulating T-follicular helper and type I regulatory T cells have overlapping phenotypes in P. falciparum malaria and are maintained by parasite exposure.

Immunity to P. falciparum malaria develops slowly, requiring repeated infection in areas of high transmission, and wanes rapidly in the absence of parasite exposure. Key to this immunity, is the development of antibodies which is supported by CD4 T follicular helper (Tfh) cells that drive robust germinal centre responses. However, in malaria, the malaria-specific CD4 T cell compartment in peripheral blood is dominated by Type 1 regulatory T cells (Tr1), which produce high levels of IL-10 in response to parasites. Tr1-like Tfh cells (Tfh10) have been reported in several settings of repeated antigen stimulation but have not been investigated in malaria. Here we used single-cell RNA sequencing and multiparameter flow cytometry to characterise malaria-specific Tfh and Tr1 cells in a longitudinal cohort of highly exposed individuals and assessed their persistence after transmission interruption. Malaria-specific Tfh and Tr1 cells shared overlapping profiles, and Tr1 cell-like transcriptional signatures and phenotypes were detectable within the Tfh cell compartment. Tfh10 cell subsets were the dominant phenotype of malaria-specific Tfh cells. Following disruption of malaria transmission, the frequencies of malaria-specific Tr1 and Tfh10 cells declined. These findings highlight a close relationship between Tfh and Tr1 cells and show that the Tfh cell compartment in malaria is dominated by Tfh10 cells. The rapid waning of these cells in the absence of continuous exposure is consistent with requirements of persistent antigen in maintaining regulatory CD4 T cell phenotypes.

immunology↗

bioRxiv2026

Splenic tropism of Plasmodium vivax in acute infection and spleen-attenuated systemic inflammation

BackgroundIn chronic asymptomatic Plasmodium vivax infections, the spleen accounts for more than 98% of total-body parasite biomass. Whether this splenic tropism also exists in acute infection and how the spleen influences pathogenesis have not been systematically explored. Materials and MethodsIn Papua, Indonesia, we compared plasma levels of P. vivax lactate dehydrogenase [PvLDH]) and circulating parasitemia in 24 spleen-intact and 25 previously splenectomized patients with acute uncomplicated vivax malaria. Clinical and hematology data were collected and plasma markers of intravascular hemolysis (cell-free hemoglobin [CFHb]), endothelial activation (angiopoietin-2), inflammation (interleukin [IL]-1 beta, IL-6, IL-18, IL-10, tumor necrosis factor-alpha) and neutrophil activation (elastase) were measured by ELISA. Giemsa-based histology in one spleen from an untreated patient splenectomized for trauma during an episode of acute vivax malaria enabled direct assessment of splenic and circulating parasitemia and biomass microscopically. ResultsCirculating parasitemia was 4-times higher in splenectomized compared to spleen-intact patients (median 21,100 vs 4,820 parasites/{micro}L, p=0.0002) but total-body P. vivax biomass (PvLDH) was 3-times lower in patients without a spleen (median 721 vs 2,140 ng/mL, p=0.026). Parasite staging and greater organ-specific symptoms suggest redistribution of parasites in the absence of a spleen. Linear regression modeling, adjusting for circulating parasitemia, patient age, sex and duration of fever, demonstrated an 8.1-fold higher PvLDH concentration in spleen-intact patients (95% confidence interval [CI]: 3.4-19.5-fold, p<0.0001), indicating a splenic biomass accounting for 89% (95%CI: 77.3-95.1%) of total-body parasites. Histopathology revealed a spleen-to-blood biomass ratio of 10.7, in-line with the PvLDH-based estimate. In spleen-intact patients, splenic P. vivax biomass correlated strongly with markers of disease intensity, endothelial activation and systemic inflammation, whereas circulating parasitemia correlated weakly or not at all. Compared to spleen-intact patients, CFHb, endothelial activation and systemic inflammation were higher in splenectomized patients while inflammasome-dependent responses were lower. ConclusionsP. vivax is predominantly an infection of the spleen, even in acute clinical vivax malaria. We conservatively estimate that 89% of total-body parasite biomass in acute infection is splenic. While the size of this hidden population correlates with disease intensity, the spleen likely regulates inflammatory pathways and heme-associated pathology.

pathology↗

bioRxiv2026

Latent cytomegalovirus disrupts NK cell responses to P. falciparum and impairs parasite control

BackgroundNK cells are major innate and adaptive responders to malaria, with multiple roles in protection. Function of NK cells is heterogeneous, underpinned by expression of a diversity of receptors. One driver of NK cell heterogeneity is latent CMV infection, which drives the expansion of memory-like NK cells. We have recently reported that latent CMV infection can negatively impact the adaptive immune response to malaria, but whether CMV-mediated changes to the NK cell compartment also impact innate responses to malaria is unknown. MethodsWe investigated the impact of latent CMV infection on NK cell response to the malaria parasite Plasmodium falciparum in vitro, and in CMV seronegative and seropositive individuals during controlled human malaria infection. We analysed NK cell activation, cytotoxicity and NK cell receptor expression. Additionally, we investigated the impact of CMV serostatus on cytokine production in response to TLR stimulation in the myeloid cell compartment. The impact of CMV and NK cell responses on parasite control and malaria symptoms was investigated. ResultsNK cells from CMV seropositive individuals had reduced responsiveness to P. falciparum parasites in vitro and had reduced activation during controlled human infection. Reduced activation was not restricted to NK subsets modulated by CMV but occurred across the entire NK cell compartment. Consistent with global NK cell attenuation, IL-12 production from myeloid cells, a response that supports NK cell activation on exposure to P. falciparum parasites, was lower in CMV infected individuals. Linking NK cell activation to clinical outcomes, NK cells expressing perforin were associated with parasite control in CMV seronegative individuals. ConclusionCMV infection modulates NK cell responses during malaria by disruption of IL-12, leading to reduced parasite control.

immunology↗

bioRxiv2025

Cytotoxic Vδ2+T cell subsets expand in response to malaria in human tonsil and spleen organoids

Vaccine effectiveness against malaria is dramatically reduced in malaria-exposed compared to malaria-naive populations, potentially due to altered immune responses in secondary lymphoid organs following repeated infection. Newly developed human tonsil and spleen organoids, which replicate key features of B and T cell immunity, provide an exciting opportunity to overcome challenges of other models and to improve our understanding of innate-adaptive interactions in lymphoid tissue. The objectives of this study were to use these organoids to investigate the impact of malaria parasites on 1) cells within lymphoid tissues and 2) responses to a heterologous antigen. When we exposed organoids from malaria-naive donors to Plasmodium falciparum-infected red blood cells (iRBC), we observed that iRBC exposure did not disrupt organoid formation and significantly increased V{delta}2+ {gamma}{delta} T cell frequencies in both tonsil and spleen organoids at multiple timepoints. Single-cell RNA/TCR sequencing revealed that iRBC-responsive V{delta}2+ T cells in organoids were clonally expanded and exhibited activated, cytotoxic phenotypes with upregulated expression of granzymes, interferon-stimulated genes, and antigen presentation machinery. TCR repertoire analysis demonstrated that malaria exposure drove clonal expansion of cytotoxic V{delta}2+ T cells, contrasting with the diverse, smaller clones observed in control conditions. To validate these findings, we analyzed tonsils from Ugandan children with asymptomatic malaria infection and found expanded V{delta}2+ T cells with enhanced cytotoxic potential compared to uninfected controls. When we tested whether malaria pre-exposure affected subsequent recall responses to influenza vaccine, malaria pre-exposure or {gamma}{delta} T cell depletion did not significantly alter cellular frequencies or influenza-specific antibody responses in most donors, though modest reductions were observed in some individuals. This work demonstrates the utility of human lymphoid organoids for studying malaria-host interactions and provides novel insights into V{delta}2+ T cell biology, including evidence for antigen-specific clonal expansion and cytotoxic differentiation in response to malaria parasites within secondary lymphoid tissues. Author SummaryMalaria vaccines are significantly less effective in populations with endemic malaria exposure compared to malaria-naive individuals. We used human tonsil and spleen organoids to investigate whether repeated malaria infections alter immune responses in secondary lymphoid organs, potentially contributing to this reduced vaccine efficacy. These organoids create a controlled system that preserves the architecture and cellular interactions of secondary lymphoid tissues. When we exposed organoids to Plasmodium falciparum-infected red blood cells, we observed dramatic expansion of the V{delta}2+ subset of {gamma}{delta} T cells. This finding was particularly noteworthy because V{delta}2+ T cells are not typically considered major participants in immune responses within secondary lymphoid organs. Single-cell analysis revealed that these expanded V{delta}2+ T cells underwent clonal expansion and acquired cytotoxic phenotypes, suggesting antigen-specific responses. Tonsil tissue from Ugandan children with asymptomatic malaria infections showed similar patterns of V{delta}2+ T cell expansion and enhanced cytotoxic potential. Surprisingly, malaria pre-exposure did not affect subsequent recall responses to influenza vaccine in most donors, although this does not discount a possible impact on immune responses to primary vaccination. Our work reveals unexpected roles for {gamma}{delta} T cells in lymphoid tissues during malaria infection and establishes organoids as valuable models for studying host-pathogen interactions.

immunology↗

bioRxiv2025

Comparison of CD4 T cell response in Plasmodium falciparum and vivax malaria

BackgroundPlasmodium falciparum and P. vivax are parasites responsible for most malaria cases globally. In areas where these species co-exist, individuals gain protection from P. vivax more rapidly, and important biological differences between species may impact the immune response. CD4 T cells are key drivers of immunity to malaria, both as effector and helper cells, with T-follicular helper (Tfh) having key roles in antibody development. Comparative studies on CD4 T cell responses between these species are limited. MethodsWe assessed CD4 T cells in adults with either P. falciparum or P. vivax malaria. Activation and proliferation of CD4 T cells were measured ex vivo, and functional capacity determined by intracellular cytokine staining by flow cytometry. ResultsThe phenotype, activation and proliferation of CD4 T cells and effector CD4 T cell subsets were comparable between species. However, within the peripheral (p)Tfh cell compartment, there was evidence for a skew towards pTfh1 cells in P. falciparum, and pTfh2 cells in P. vivax. Additionally, in P. falciparum, increased IL-10 production was detected, including within IL-21 producing CD4 T cells. ConclusionWhile activation and function of CD4 T cells in malaria are largely comparable, some species-dependent responses are detected within the pTfh cell compartment that may impact antibody development.

immunology↗