Cytokine responses to malaria play important roles in both protective immunity development and pathogenesis. Although the roles of cytokines such as TNF-α, IL-12, IFN-γ, and IL-10 in immunity and pathogenesis to the blood stage malaria are largely known, the role of IL-4 remains less understood. IL-4 targets many cell types and induces multiple effects, including cell proliferation, gene expression, protection from apoptosis, and immune regulation. Accordingly, IL-4 has been exploited as a therapeutic for several inflammatory diseases. Malaria caused by Plasmodium falciparum manifests in many organ-specific fatal pathologies, including cerebral malaria (CM), driven by a high parasite load, leading to parasite sequestration in organs and consequent excessive inflammatory responses and endothelial damage. We investigated the therapeutic potential of IL-4 against fatal malaria in Plasmodium berghei ANKA–infected C57BL/6J mice, an experimental CM model. IL-4 treatment significantly reduced parasitemia, CM pathology, and mortality. The therapeutic effect of IL-4 is mediated through multiple mechanisms, including enhanced parasite clearance mediated by upregulation of phagocytic receptors and increased IgM production, and decreased brain inflammatory responses, including reduced chemokine (CXCL10) production, reduced chemokine receptor (CXCR3) and adhesion molecule (LFA-1) expression by T cells, and downregulation of cytotoxic T cell lytic potential. IL-4 treatment markedly reduced the infiltration of CD8⁺ T cells and brain pathology. STAT6, PI3K–Akt–NF-κB, and Src signaling mediated the cellular and molecular events that contributed to the IL-4–dependent decrease in parasitemia. Overall, our results provide mechanistic insights into how IL-4 treatment mitigates experimental CM and have implications in developing treatment strategies for organ-specific fatal malaria. Key Points Exogenous IL-4 reduces parasitemia and prevents experimental cerebral malaria. IL-4 increases phagocytic receptor expression, B1 cell expansion, and IgM production. IL-4 reduces cytotoxicity and infiltration of CD8⁺ T cells in cerebral malaria model.

Potassium ions (K⁺) are critical electrolytes that regulate multiple functions in immune cells. Recent studies have shown that the elevated concentration of extracellular potassium in the tumor interstitial fluid limits T cell effector function and suppresses the anti-tumor capacity of tumor-associated macrophages (TAMs). The effect of excess potassium on the biology of myeloid-derived suppressor cells (MDSCs), another important immune cell component of the tumor microenvironment (TME), is unknown. Here, we present data showing that increased concentrations of potassium chloride (KCl), as the source of K⁺ ions, facilitate autophagy by increasing the expression of the autophagosome marker LC3β. Simultaneously, excess potassium ions significantly decrease the expression of arginase I (Arg I) and inducible nitric oxide synthase (iNOS) without reducing the ability of MDSCs to suppress T cell proliferation. Further investigation reveals that excess K⁺ ions decrease the expression of the transcription factor C/EBP-β and alter the expression of phosphorylated kinases. While excess K⁺ ions downregulated the expression levels of phospho-AMPKα (pAMPKα), it increased the levels of pAKT and pERK. Additionally, potassium increased mitochondrial respiration as measured by the oxygen consumption rate (OCR). Interestingly, all these alterations induced by K⁺ ions were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Our results suggest that hyperosmotic stress caused by excess K⁺ ions regulate the mitochondrial respiration and signaling pathways in MDSCs to trigger the process of autophagy to support MDSCs’ immunosuppressive function by mechanisms independent of Arg I and iNOS. Overall, our in vitro and ex vivo findings offer valuable insights into the adaptations of MDSCs within the K⁺ ion-rich TME, which has important implications for MDSCs-targeted therapies.

Malaria infection causes multiple organ-specific lethal pathologies, including cerebral malaria, and severe liver and lung pathologies by inducing strong inflammatory responses. Gene polymorphism studies suggest that TLR4 and TLR2 contribute to severe malaria, but the roles of these signaling molecules in malaria pathogenesis remain incompletely understood. We hypothesize that danger-associated molecular patterns (DAMPs) produced in response to malaria activate TLR2 and TLR4 signaling and contribute to liver and lung pathologies. By using a mouse model of Plasmodium berghei NK65 infection, we show that the combined TLR2 and TLR4 signaling contributes to malaria liver and lung pathologies, and mortality. Macrophages, neutrophils, NK cells, and T cells infiltrate to the livers and lungs of infected wild type (WT) mice more than TLR2,4^-/- mice. Additionally, endothelial barrier disruption, tissue necrosis, and hemorrhage were higher in the livers and lungs of infected WT mice than in those of TLR2,4^-/- mice. Consistent with these results, the levels of chemokine production, chemokine receptor expression, and liver and lung pathological markers were higher in infected WT mice than in TLR2,4^-/- mice. In addition, the levels of HMGB1, a potent TLR2- and TLR4-activating DAMP, were higher in livers and lungs of WT mice than TLR2,4^-/- mice. Treatment with glycyrrhizin, an immunomodulatory agent known to inhibit HMGB1 activity, markedly reduced mortality in WT mice. These results suggest that TLR2 and TLR4 activation by HMGB1 and possibly other endogenously produced DAMPs contribute to malaria liver and lung injury via signaling mechanisms distinct from those involved in cerebral malaria pathogenesis.

G protein–coupled receptor 84 (GPR84) is a medium-chain free fatty acid receptor predominantly expressed in myeloid cells. Previous studies have identified GPR84 as an enhancer of the pro-inflammatory myeloid cell responses and a regulator of metabolic homeostasis. However, the role of GPR84 in T-cell function and metabolism remains largely unexplored. This study tested the effect of GPR84 modulation on CD8+ T-cell function and metabolism in vitro and examined its effect on antitumor function in adoptive cellular therapy models. Pharmacologic antagonism with GLPG1205 or genetic deletion of GPR84 promoted T-cell differentiation, proliferation, cytokine production, and cytotoxicity, whereas agonism with DL175 reduced these functions. These functional changes were paralleled by changes in metabolic activity. Antagonism and genetic deletion increased glucose uptake, glycolysis, oxidative phosphorylation, and ATP production, which enhanced the overall cell energetic fitness, whereas agonism resulted in a quiescent energetic profile. Furthermore, antagonism or deletion of GPR84 in antigen-specific CD8+ T cells in adoptive cellular therapy models enhanced their antitumor effects in vivo. Thus, GPR84 inhibition improves CD8+ T-cell function and may further enhance adoptive cellular therapies.