Blockade of LAG-3 in PD-L1-Deficient Mice Enhances Clearance of Blood Stage Malaria Independent of Humoral Responses

Characteristics of splenic PD-1+ γδT cells in Plasmodium yoelii nigeriensis infection

Although the functions of programmed death-1 (PD-1) on αβ T cells have been extensively reported, a role for PD-1 in regulating γδT cell function is only beginning to emerge. Here, we investigated the phenotypic and functional characteristics of PD-1-expressing γδT cells, and the molecular mechanism was also explored in the Plasmodium yoelii nigeriensis (P. yoelii NSM)-infected mice. Flow cytometry and single-cell RNA sequencing (scRNA-seq) were performed. An inverse agonist of RORα, SR3335, was used to investigate the role of RORα in regulating PD-1+ γδT cells. The results indicated that γδT cells continuously upregulated PD-1 expression during the infection period. Higher levels of CD94, IL-10, CX3CR1, and CD107a; and lower levels of CD25, CD69, and CD127 were found in PD-1+ γδT cells from infected mice than in PD-1- γδT cells. Furthermore, GO enrichment analysis revealed that the marker genes in PD-1+ γδT cells were involved in autophagy and processes utilizing autophagic mechanisms. ScRNA-seq results showed that RORα was increased significantly in PD-1+ γδT cells. GSEA identified that RORα was mainly involved in the regulation of I-kappaB kinase/NF-κB signaling and the positive regulation of cytokine production. Consistent with this, PD-1-expressing γδT cells upregulated RORα following Plasmodium yoelii infection. Additionally, in vitro studies revealed that higher levels of p-p65 were found in PD-1+ γδT cells after treatment with a RORα selective synthetic inhibitor. Collectively, these data suggest that RORα-mediated attenuation of NF-κB signaling may be fundamental for PD-1-expressing γδT cells to modulate host immune responses in the spleen of Plasmodium yoelii nigeriensis-infected C57BL/6 mice, and it requires further investigation.

IL-15 Complex-Induced IL-10 Enhances Plasmodium-specific CD4+ T Follicular Helper Differentiation and Antibody Production

Malaria, which results from infection with Plasmodium parasites, remains a major public health problem. Although humans do not develop long-lived, sterilizing immunity, protection against symptomatic disease develops after repeated exposure to Plasmodium parasites and correlates with the acquisition of humoral immunity. Despite the established role Abs play in protection from malaria disease, dysregulated inflammation is thought to contribute to the suboptimal immune response to Plasmodium infection. Plasmodium berghei ANKA (PbA) infection results in a fatal severe malaria disease in mice. We previously demonstrated that treatment of mice with IL-15 complex (IL-15C; IL-15 bound to an IL-15Rα-Fc fusion protein) induces IL-10 expression in NK cells, which protects mice from PbA-induced death. Using a novel MHC class II tetramer to identify PbA-specific CD4+ T cells, in this study we demonstrate that IL-15C treatment enhances T follicular helper (Tfh) differentiation and modulates cytokine production by CD4+ T cells. Moreover, genetic deletion of NK cell-derived IL-10 or IL-10R expression on T cells prevents IL-15C-induced Tfh differentiation. Additionally, IL-15C treatment results in increased anti-PbA IgG Ab levels and improves survival following reinfection. Overall, these data demonstrate that IL-15C treatment, via its induction of IL-10 from NK cells, modulates the dysregulated inflammation during Plasmodium infection to promote Tfh differentiation and Ab generation, correlating with improved survival from reinfection. These findings will facilitate improved control of malaria infection and protection from disease by informing therapeutic strategies and vaccine design.

Cytolytic circumsporozoite-specific memory CD4+ T cell clones are expanded during Plasmodium falciparum infection

Clinical immunity against Plasmodium falciparum infection develops in residents of malaria endemic regions, manifesting in reduced clinical symptoms during infection and in protection against severe disease but the mechanisms are not fully understood. Here, we compare the cellular and humoral immune response of clinically immune (0-1 episode over 18 months) and susceptible (at least 3 episodes) during a mild episode of Pf malaria infection in a malaria endemic region of Malawi, by analysing peripheral blood samples using high dimensional mass cytometry (CyTOF), spectral flow cytometry and single-cell transcriptomic analyses. In the clinically immune, we find increased proportions of circulating follicular helper T cells and classical monocytes, while the humoral immune response shows characteristic age-related differences in the protected. Presence of memory CD4+ T cell clones with a strong cytolytic ZEB2+ T helper 1 effector signature, sharing identical T cell receptor clonotypes and recognizing the Pf-derived circumsporozoite protein (CSP) antigen are found in the blood of the Pf-infected participants gaining protection. Moreover, in clinically protected participants, ZEB2+ memory CD4+ T cells express lower level of inhibitory and chemotactic receptors. We thus propose that clonally expanded ZEB2+ CSP-specific cytolytic memory CD4+ Th1 cells may contribute to clinical immunity against the sporozoite and liver-stage Pf malaria.

Drug Development Strategies for Malaria: With the Hope for New Antimalarial Drug Discovery—An Update

Malaria continued to be a deadly situation for the people of tropical and subtropical countries. Although there has been a marked reduction in new cases as well as mortality and morbidity rates in the last two decades, the reporting of malaria caused 247 million cases and 619000 deaths worldwide in 2021, according to the WHO (2022). The development of drug resistance and declining efficacy against most of the antimalarial drugs/combination in current clinical practice is a big challenge for the scientific community, and in the absence of an effective vaccine, the problem becomes worse. Experts from various research organizations worldwide are continuously working hard to stop this disaster by employing several strategies for the development of new antimalarial drugs/combinations. The current review focuses on the history of antimalarial drug discovery and the advantages, loopholes, and opportunities associated with the common strategies being followed for antimalarial drug development.

Clinical Significance of Soluble LAG-3 (sLAG-3) in Patients With Cervical Cancer Determined via Enzyme-Linked Immunosorbent Assay With Monoclonal Antibodies

Background: The tumor microenvironment and tumor immunity have become the focus of research on tumor diagnosis and treatment. Lymphocyte activation gene-3 (LAG-3, CD223) is a newly discovered immunosuppressive receptor that is abnormally expressed in various tumor microenvironments and plays an important role as an immune checkpoint in the tumor immune response. Objective: We developed a novel enzyme-linked immunosorbent assay kit, examined the levels of soluble LAG-3 (sLAG-3) in the serum of patients with cervical cancer, and identified new biomarkers for cervical cancer development. Methods: To investigate the potential biological function of sLAG-3, we generated and characterized 2 novel anti-LAG-3 monoclonal antibodies, namely 4F4 and 4E12. We performed western blotting, immunofluorescence, and immunohistochemistry using hybridoma technology and an enzyme-linked immunosorbent assay kit for detecting human sLAG-3 based on an improved double-antibody sandwich enzyme-linked immunosorbent assay method. The stability and sensitivity of these kits were also assessed. Results: We screened and characterized 2 novel monoclonal antibodies against human LAG-3. The enzyme-linked immunosorbent assay kit also includes a wide range of tests. Using this enzyme-linked immunosorbent assay system, we found that the expression level of sLAG-3 in the peripheral blood of patients with cervical cancer significantly decreased as the disease progressed (P < .0001). Multivariate logistic regression analysis revealed that low sLAG-3 expression was an independent predictor of cervical cancer and related diseases (P < .05). Furthermore, receiver operating characteristic curve analysis showed that sLAG-3 had diagnostic value for cervical cancer metastasis (P < .0001). Conclusion: These data suggest that sLAG-3 is a potential biomarker for cervical cancer development. Therefore, this kit has a certain application value in the diagnosis of cervical cancer.

Excretory/secretory proteins inhibit host immune responses by downregulating the TLR4/NF-κB/MAPKs signaling pathway: A possible mechanism of immune evasion in parasitic nematode Haemonchus contortus

Haemonchus contortus is an important parasitic nematode of ruminants. Previous studies showed that H. contortus escape the immunity through complex mechanisms, including releasing excretory/secretory proteins (ESPs) to modulate the host immune response. However, the detailed mechanism through which H. contortus excretory/secretory proteins (HcESPs) promote immune evasion remains unknown. In the present study, we demonstrated that HcESPs inhibit the adaptive immune response of goats including downregulation of immune cell antigen presentation, upregulation of immune checkpoint molecules, activation of the STAT3/PD-L1 pathway, and activation of immunosuppressive regulatory T (Treg) cells. Furthermore, HcESPs reversed the LPS-induced upregulation of pro-inflammatory mediators in PBMCs by inhibiting the TLR4/NF-κB/MAPKs/NLRP3 signaling pathway. Our study provides a better understanding of the evasion mechanisms for H. contortus, which could be helpful in providing an alternative way to prevent the infection of this parasite.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

Deciphering the Plasmodium falciparum malaria-specific CD4+ T-cell response: ex vivo detection of high frequencies of PD-1+TIGIT+ EXP1-specific CD4+ T cells using a novel HLA-DR11-restricted MHC class II tetramer

Relatively little is known about the ex vivo frequency and phenotype of the Plasmodium falciparum-specific CD4+ T-cell response in humans. The exported protein 1 (EXP1) is expressed by plasmodia at both, the liver stage and blood stage, of infection making it a potential target for CD4+ and CD8+ effector T cells. Here, a fluorochrome-labelled HLA-DRB1∗11:01-restriced MHC class II tetramer derived from the P. falciparum EXP1 (aa62-74) was established for ex vivo tetramer analysis and magnetic bead enrichment in 10 patients with acute malaria. EXP1-specific CD4+ T cells were detectable in 9 out of 10 (90%) malaria patients expressing the HLA-DRB1∗11 molecule with an average ex vivo frequency of 0.11% (0-0.22%) of total CD4+ T cells. The phenotype of EXP1-specific CD4+ T cells was further assessed using co-staining with activation (CD38, HLA-DR, CD26), differentiation (CD45RO, CCR7, KLRG1, CD127), senescence (CD57), and co-inhibitory (PD-1, TIGIT, LAG-3, TIM-3) markers as well as the ectonucleotidases CD39 and CD73. EXP1-specific tetramer+ CD4+ T cells had a distinct phenotype compared to bulk CD4+ T cells and displayed a highly activated effector memory phenotype with elevated levels of co-inhibitory receptors and activation markers: EXP1-specific CD4+ T cells universally expressed the co-inhibitory receptors PD-1 and TIGIT as well as the activation marker CD38 and showed elevated frequencies of CD39. These results demonstrate that MHC class II tetramer enrichment is a sensitive approach to investigate ex vivo antigen-specific CD4+ T cells in malaria patients that will aid further analysis of the role of CD4+ T cells during malaria.