Insights on Host-Parasite Immunomodulation Mediated by Extracellular Vesicles of Cutaneous Leishmania shawi and Leishmania guyanensis

Unveiling the Interplay Between Dendritic Cells and Natural Killer Cells as Key Players in Leishmania Infection

Leishmaniasis is a group of parasitic diseases whose etiological agent is the protozoa Leishmania. These diseases afflict impoverished populations in tropical and subtropical regions and affect wild and domestic animals. Canine leishmaniasis is a global disease mostly caused by L. infantum. Dogs are recognized as a good reservoir since harbor the infection long before developing the disease, facilitating parasite transmission. Furthermore, there is growing evidence that dogs may also be the reservoir of the American Leishmania spp. as L. amazonensis. The innate immune response is the first defense line against pathogens, which includes natural killer (NK) and dendritic cells (DCs). By recognizing and ultimately destroying infected cells, and by secreting immune mediators that favor inflammatory microenvironments, NK cells take the lead in the infectious process. When interacting with Leishmania parasites, DCs become activated and play a key role in driving the host immune response. While activated DCs can modulate NK cell activity, Leishmania parasites can directly activate NK cells by interacting with innate immune receptors. Once activated, NK cells can engage in a bidirectional interplay with DCs. However, the complexity of these interactions during Leishmania infection makes it challenging to fully understand the underlying processes. To further explore this, the present study investigated the dynamic interplay established between monocyte-derived DCs (moDCs) and putative NK (pNK) cells of dogs during Leishmania infection. Findings indicate that the crosstalk between moDCs exposed to L. infantum or L. amazonensis and pNK cells enhances chemokine upregulation, potentially attracting other leukocytes to the site of infection. pNK cells activated by L. infantum infected DCs upregulate IL-10, which can lead to a regulatory immune response while moDCs exposed to L. amazonensis induced pNK cells to overexpress IFN-γ and IL-13, favoring a mix of pro- and anti-inflammatory response. In addition, parasite-derived extracellular vesicles (EVs) can modulate the host immune response by stimulating the upregulation of anti-inflammatory cytokines and perforin release, which may impact infection outcomes. Thus, Leishmania and parasitic EVs can influence the bidirectional interplay between canine NK cells and DCs.

Microbiome and Mucosal Immunity in the Intestinal Tract

The human bowel is exposed to numerous biotic and abiotic external noxious agents. Accordingly, the digestive tract is frequently involved in malfunctions within the organism. Together with the commensal intestinal flora, it regulates the immunological balance between inflammatory defense processes and immune tolerance. Pathological changes in this system often cause chronic inflammatory bowel diseases including Crohn's disease and ulcerative colitis. This review article highlights the complex interaction between commensal microorganisms, the intestinal microbiome, and the intestinal epithelium-localized local immune system. The main functions of the human intestinal microbiome include (i) protection against pathogenic microbial colonization, (ii) maintenance of the barrier function of the intestinal epithelium, (iii) degradation and absorption of nutrients and (iv) active regulation of the intestinal immunity. The local intestinal immune system consists primarily of macrophages, antigen-presenting cells, and natural killer cells. These cells regulate the commensal intestinal microbiome and are in turn regulated by signaling factors of the epithelial cells and the microbiome. Deregulated immune responses play an important role and can lead to both reduced activity of the commensal microbiome and pathologically increased activity of harmful microorganisms. These aspects of chronic inflammatory bowel disease have become the focus of attention in recent years. It is therefore important to consider the immunological-microbial context in both the diagnosis and treatment of inflammatory bowel diseases. A promising holistic approach would include the most comprehensive possible diagnosis of the immune and microbiome status of the patient, both at the time of diagnostics and during therapy.

Extracellular Vesicles Derived From Entamoeba histolytica Have an Immunomodulatory Effect on THP-1 Macrophages

Recent studies have shown that extracellular vesicles (EVs) secreted by various parasites are capable of modulating the host's innate immune responses, such as by altering macrophage (Mϕ) phenotypes and functions. Studies have shown that Mϕ promote early host responses to amoebic infection by releasing proinflammatory cytokines that are crucial to combating amoebiasis. Here, we are reporting for the first time the effect of EVs released by Entamoeba histolytica (EhEVs) on human THP-1 differentiated Mϕ (THP-1 Mϕ). We show that the EhEVs are internalized by THP-1 Mϕ which leads to differential regulation of various cytokines associated with both M1 and M2 Mϕ. We also saw that EhEV treatment thwarted Type 2 immune-response-related transcriptome pSTAT6 in the THP-1 Mϕ. Furthermore, EhEVs stimulated Mϕ to reduce their energy demand by suppressing oxidative phosphorylation (OXPHOS) and adenosine triphosphate (ATP) production. Hence, the human parasite E. histolytica-derived EVs are capable of eliciting an immune response from Mϕ that may contribute to overall infection status.

An in-depth exploration of the multifaceted roles of EVs in the context of pathogenic single-cell microorganisms

SUMMARYExtracellular vesicles (EVs) have been recognized throughout scientific communities as potential vehicles of intercellular communication in both eukaryotes and prokaryotes, thereby influencing various physiological and pathological functions of both parent and recipient cells. This review provides an in-depth exploration of the multifaceted roles of EVs in the context of bacteria and protozoan parasite EVs, shedding light on their contributions to physiological processes and disease pathogenesis. These studies highlight EVs as a conserved mechanism of cellular communication, which may lead us to important breakthroughs in our understanding of infection, mechanisms of pathogenesis, and as indicators of disease. Furthermore, EVs are involved in host-microbe interactions, offering insights into the strategies employed by bacteria and protozoan parasites to modulate host responses, evade the immune system, and establish infections.

Extracellular vesicles in parasitic diseases - from pathogenesis to future diagnostic tools

Parasitic diseases are still a major public health problem especially among individuals of low socioeconomic status in underdeveloped countries. In recent years it has been demonstrated that parasites can release extracellular vesicles that participate in the host-parasite communication, immune evasion, and in governing processes associated with host infection. Extracellular vesicles are membrane-bound structures released into the extracellular space that can carry several types of biomolecules, including proteins, lipids, nucleic acids, and metabolites, which directly impact the target cells. Extracellular vesicles have attracted wide attention due to their relevance in host-parasite communication and for their potential value in applications such as in the diagnostic biomarker discovery. This review of the literature aimed to join the current knowledge on the role of extracellular vesicles in host-parasite interaction and summarize its molecular content, providing information for the acquisition of new tools that can be used in the diagnosis of parasitic diseases. These findings shed light to the potential of extracellular vesicle cargo derived from protozoan parasites as novel diagnostic tools.

Exploiting Leishmania-Primed Dendritic Cells as Potential Immunomodulators of Canine Immune Response

Dendritic cells (DCs) capture pathogens and process antigens, playing a crucial role in activating naïve T cells, bridging the gap between innate and acquired immunity. However, little is known about DC activation when facing Leishmania parasites. Thus, this study investigates in vitro activity of canine peripheral blood-derived DCs (moDCs) exposed to L. infantum and L. amazonensis parasites and their extracellular vesicles (EVs). L. infantum increased toll-like receptor 4 gene expression in synergy with nuclear factor κB activation and the generation of pro-inflammatory cytokines. This parasite also induced the expression of class II molecules of major histocompatibility complex (MHC) and upregulated co-stimulatory molecule CD86, which, together with the release of chemokine CXCL16, can attract and help in T lymphocyte activation. In contrast, L. amazonensis induced moDCs to generate a mix of pro- and anti-inflammatory cytokines, indicating that this parasite can establish a different immune relationship with DCs. EVs promoted moDCs to express class I MHC associated with the upregulation of co-stimulatory molecules and the release of CXCL16, suggesting that EVs can modulate moDCs to attract cytotoxic CD8+ T cells. Thus, these parasites and their EVs can shape DC activation. A detailed understanding of DC activation may open new avenues for the development of advanced leishmaniasis control strategies.

Extracellular Vesicles and Their Impact on the Biology of Protozoan Parasites

Extracellular vesicles (EVs) are lipid-membrane-bound structures produced naturally by all cells and have a variety of functions. EVs act as vehicles for transporting important molecular signals from one cell to another. Several parasites have been shown to secrete EVs, and their biological functions have been extensively studied. EVs have been shown to facilitate communication with the host cells (such as modulation of the host's immune system or promoting attachment and invasion into the host cells) or for communication between parasitic cells (e.g., transferring drug-resistance genes or factors modulating stage conversion). It is clear that EVs play an important role in host-parasite interactions. In this review, we summarized the latest research on the EVs secreted by protozoan parasites and their role in host-parasite and parasite-parasite communications.

A Difficult-To-Diagnose Case of American Tegumentary Leishmaniasis

This case report presents a difficult-to-diagnose case of American tegumentary leishmaniasis (ATL) caused by Leishmania (Viannia) guyanensis in a 24-year-old Hispanic male with a travel history to the Panama jungle, an endemic region for tropical infectious diseases. The patient initially presented with persistent skin lesions that progressed to abscesses with ulceration. Despite negative initial diagnostic tests, including microbiological investigations and histopathological examination, a comprehensive diagnostic workup and subsequent polymerase chain reaction (PCR) confirmed the presence of Leishmania parasites. This case underscores the need to consider tropical infectious diseases despite initial negative tests. Accurate species identification is vital for proper drug treatment, with miltefosine as an emerging option. Early, precise diagnosis and tailored management are essential for successful treatment. This report emphasizes the significance of conducting a comprehensive diagnostic workup, including PCR, in individuals with a history of travel to endemic regions, to accurately diagnose and effectively manage complex infectious diseases.

Exosome-derived long noncoding RNAs: Mediators of host-Plasmodium parasite communication

Overcoming challenges associated with malaria eradication proves to be a formidable task due to the complicated life cycle exhibited by the malaria parasite and the lack of safe and enduring vaccines against malaria. Investigating the interplay between Plasmodium parasites and their mammalian hosts is crucial for the development of novel vaccines. Long noncoding RNAs (lncRNAs) derived from Plasmodium parasites or host cells have emerged as potential signaling molecules involved in the trafficking of proteins, RNA (mRNAs, miRNAs, and ncRNAs), and DNA. These lncRNAs facilitate the interaction between hosts and parasites, impacting normal physiology or pathology in malaria-infected individuals. Moreover, they possess the capacity to regulate immune responses and associated signaling pathways, thus potentially influencing chromatin organization, epigenetic modifications, mRNA processing, splicing, and translation. However, the functional role of exosomal lncRNAs in malaria remains poorly understood. This review offers a comprehensive analysis of lncRNA and exosomal lncRNA profiles during malaria infection. It presents an overview of recent progress in elucidating the involvement of exosomal lncRNAs in host-parasite interactions. Additionally, potential exosomal lncRNAs linked to the domains of innate and adaptive immunity in the context of malaria are proposed. These findings may contribute to the discovery of new diagnostic and therapeutic strategies for malaria. Furthermore, the need for additional research was highlighted that aimed to elucidate the mechanisms underlying lncRNA transportation into host cells and their targeting of specific genes to regulate the host's immune response. This knowledge gap presents an opportunity for future investigations, offering innovative approaches to enhance malarial control. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Small Molecule-RNA Interactions RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA in Disease and Development > RNA in Disease.