CD14+ monocytes are the main leucocytic sources of CXCL10 in response to Plasmodium falciparum

Extracellular vesicles in malaria: Pathogenesis, diagnosis and therapy

Malaria is a life-threatening disease caused by parasites from the genus Plasmodium. Five species can cause malaria in humans, with Plasmodium vivax being the most common in many countries and Plasmodium falciparum having the highest lethality, which can lead to cerebral malaria. Extracellular vesicles (EVs) are in focus in malaria research to better understand pathogenesis, diagnosis, therapy, and prognosis. Malaria-causing parasites use EVs to transfer their molecules to host cells, a mechanism that significantly contributes to parasite survival and successful infection. EVs have thus emerged as an essential component of the immunopathological cascade of malaria, playing a pivotal role in disease progression and severity. This chapter discusses the epidemiology and pathogenesis of malaria and the role of EVs as new diagnostic and therapeutic tools, emphasizing their potential clinical significance.

Obesity-related Plasma CXCL10 Drives CX3CR1-dependent Monocytic Secretion of Macrophage Migration Inhibitory Factor

Obesity is characterized by excessive body fat accumulation and comorbidities such as diabetes mellitus, cardiovascular disease, and obstructive sleep apnea syndrome (OSAS). Both obesity and OSAS are associated with immune disturbance, alterations of systemic inflammatory mediators, and immune cell recruitment to metabolic tissues. Chemokine CXCL10 is an important regulator of proinflammatory immune responses and is significantly increased in patients with severe obesity. This research project aims to investigate the impact of CXCL10 on human monocytes in patients with obesity. We studied the distribution of the CD14/CD16 monocyte subsets as well as their CX3CR1 expression patterns in whole-blood measurements from 92 patients with obesity and/or OSAS with regard to plasma CXCL10 values and individual clinical parameters. Furthermore, cytokine secretion by THP-1 monocytes in response to CXCL10 was analyzed. Data revealed significantly elevated plasma CXCL10 in patients with obesity with an additive effect of OSAS. CXCL10 was found to drive monocytic secretion of macrophage migration inhibitory factor via receptor protein CX3CR1, which significantly correlated with the individual body mass index. Our data show, for the first time, to our knowledge, that CX3CR1 is involved in alternative CXCL10 signaling in human monocytes in obesity-related inflammation. Obesity is a multifactorial disease, and further investigations regarding the complex interplay between obesity-related inflammatory mediators and systemic immune balances will help to better understand and improve the individual situation of our patients.

Listeria monocytogenes Inoculation Impedes the Development of Brain Pathology in Experimental Cerebral Malaria by Inhibition of Parasitemia

Cerebral malaria (CM) is a serious central nervous system dysfunction caused by Plasmodium falciparum infection. In this study, we investigated the effect of Listeria monocytogenes (Lm) inoculation on experimental cerebral malaria (ECM) using Plasmodium berghei ANKA (PbA)-infected C57BL/6 mice. Live Lm inoculation inhibited the parasitemia and alleviated ECM symptoms. The protective effect against ECM symptoms was connected with improved brain pathology manifested as a less-damaged blood-brain barrier, decreased parasite sequestration, and milder local inflammation. Meanwhile, Lm inoculation decreased expression of cell adhesion molecules (ICAM-1 and VCAM-1) and accumulation of pathogenic CD8⁺ T cells in the brain. In keeping with the suppression of parasitemia, there was an upregulation of IFN-γ, IL-12, MCP-1, and NO expression in the spleen by Lm inoculation upon PbA infection. Early treatment with exogenous IFN-γ exhibited a similar effect to Lm inoculation on PbA infection. Taken together, Lm inoculation impedes the development of brain pathology in ECM, and early systemic IFN-γ production may play a critical role in these protective effects.

TNF-α Increases IP-10 Expression in MCF-7 Breast Cancer Cells via Activation of the JNK/c-Jun Pathways

IP-10 (also called CXCL10) plays a significant role in leukocyte homing to inflamed tissues, and increased IP-10 levels are associated with the pathologies of various inflammatory disorders, including type 2 diabetes, atherosclerosis, and cancer. TNF-α is a potent activator of immune cells and induces inflammatory cytokine expression in these cells. However, it is unclear whether TNF-α is able to induce IP-10 expression in MCF-7 breast cancer cells. We therefore determined IP-10 expression in TNF-α-treated MCF-7 cells and investigated the mechanism involved. Our data show that TNF-α induced/upregulated the IP-10 expression at both mRNA and protein levels in MCF-7 cells. Inhibition of JNK (SP600125) significantly suppressed the TNF-α-induced IP-10 in MCF-7 cells, while the inhibition of p38 MAPK (SB203580), MEK1/2 (U0126), and ERK1/2 (PD98059) had no significant effect. Furthermore, TNF-α-induced IP-10 expression was abolished in MCF-7 cells deficient in JNK. Similar results were obtained using MCF-7 cells deficient in c-Jun. Moreover, the JNK kinase inhibitor markedly reduced the TNF-α-induced JNK and c-Jun phosphorylation. The kinase activity of JNK induced by TNF-α stimulation of MCF-7 cells was significantly inhibited by SP600125. Altogether, our novel findings provide the evidence that TNF-α induces IP-10 expression in MCF-7 breast cancer cells via activation of the JNK/c-Jun signaling pathway.

Malaria parasites both repress host CXCL10 and use it as a cue for growth acceleration

Pathogens are thought to use host molecular cues to control when to initiate life-cycle transitions, but these signals are mostly unknown, particularly for the parasitic disease malaria caused by Plasmodium falciparum. The chemokine CXCL10 is present at high levels in fatal cases of cerebral malaria patients, but is reduced in patients who survive and do not have complications. Here we show a Pf 'decision-sensing-system' controlled by CXCL10 concentration. High CXCL10 expression prompts P. falciparum to initiate a survival strategy via growth acceleration. Remarkably, P. falciparum inhibits CXCL10 synthesis in monocytes by disrupting the association of host ribosomes with CXCL10 transcripts. The underlying inhibition cascade involves RNA cargo delivery into monocytes that triggers RIG-I, which leads to HUR1 binding to an AU-rich domain of the CXCL10 3'UTR. These data indicate that when the parasite can no longer keep CXCL10 at low levels, it can exploit the chemokine as a cue to shift tactics and escape.

Factors influencing phagocytosis of malaria parasites: the story so far

There are seven known species of Plasmodium spp. that can infect humans. The human host can mount a complex network of immunological responses to fight infection and one of these immune functions is phagocytosis. Effective and timely phagocytosis of parasites, accompanied by the activation of a regulated inflammatory response, is beneficial for parasite clearance. Functional studies have identified specific opsonins, particularly antibodies and distinct phagocyte sub-populations that are associated with clinical protection against malaria. In addition, cellular and molecular studies have enhanced the understanding of the immunological pathways and outcomes following phagocytosis of malaria parasites. In this review, an integrated view of the factors that can affect phagocytosis of infected erythrocytes and parasite components, the immunological consequences and their association with clinical protection against Plasmodium spp. infection is provided. Several red blood cell disorders and co-infections, and drugs that can influence phagocytic capability during malaria are also discussed. It is hoped that an enhanced understanding of this immunological process can benefit the design of new therapeutics and vaccines to combat this infectious disease.