The scavenger receptor MARCO is involved inLeishmania majorinfection by CBA/J macrophages

From Defense to Dysfunction: Autophagy's Dual Role in Disease Pathophysiology

Autophagy is a fundamental pillar of cellular resilience, indispensable for maintaining cellular health and vitality. It coordinates the meticulous breakdown of cytoplasmic macromolecules as a guardian of cell metabolism, genomic integrity, and survival. In the complex play of biological warfare, autophagy emerges as a firm defender, bravely confronting various pathogenic, infectious, and cancerous adversaries. Nevertheless, its role transcends mere defense, wielding both protective and harmful effects in the complex landscape of disease pathogenesis. From the onslaught of infectious outbreaks to the devious progression of chronic lifestyle disorders, autophagy emerges as a central protagonist, convolutedly shaping the trajectory of cellular health and disease progression. In this article, we embark on a journey into the complicated web of molecular and immunological mechanisms that govern autophagy's profound influence over disease. Our focus sharpens on dissecting the impact of various autophagy-associated proteins on the kaleidoscope of immune responses, spanning the spectrum from infectious outbreaks to chronic lifestyle ailments. Through this voyage of discovery, we unveil the vast potential of autophagy as a therapeutic linchpin, offering tantalizing prospects for targeted interventions and innovative treatment modalities that promise to transform the landscape of disease management.

Physical Interactions With Bacteria and Protozoan Parasites Establish the Scavenger Receptor SSC4D as a Broad-Spectrum Pattern Recognition Receptor

Since the pioneering discoveries, by the Nobel laureates Jules Hoffmann and Bruce Beutler, that Toll and Toll-like receptors can sense pathogenic microorganisms and initiate, in vertebrates and invertebrates, innate immune responses against microbial infections, many other families of pattern recognition receptors (PRRs) have been described. One of such receptor clusters is composed by, if not all, at least several members of the scavenger receptor cysteine-rich (SRCR) superfamily. Many SRCR proteins are plasma membrane receptors of immune cells; however, a small subset consists of secreted receptors that are therefore in circulation. We here describe the first characterization of biological and functional roles of the circulating human protein SSC4D, one of the least scrutinized members of the family. Within leukocyte populations, SSC4D was found to be expressed by monocytes/macrophages, neutrophils, and B cells, but its production was particularly evident in epithelial cells of several organs and tissues, namely, in the kidney, thyroid, lung, placenta, intestinal tract, and liver. Similar to other SRCR proteins, SSC4D shows the capacity of physically binding to different species of bacteria, and this opsonization can increase the phagocytic capacity of monocytes. Importantly, we have uncovered the capacity of SSC4D of binding to several protozoan parasites, a singular feature seldom described for PRRs in general and here demonstrated for the first time for an SRCR family member. Overall, our study is pioneer in assigning a PRR role to SSC4D.

Stabilin-1 plays a protective role against Listeria monocytogenes infection through the regulation of cytokine and chemokine production and immune cell recruitment

Scavenger receptors are part of a complex surveillance system expressed by host cells to efficiently orchestrate innate immune response against bacterial infections. Stabilin-1 (STAB-1) is a scavenger receptor involved in cell trafficking, inflammation, and cancer; however, its role in infection remains to be elucidated. Listeria monocytogenes (Lm) is a major intracellular human food-borne pathogen causing severe infections in susceptible hosts. Using a mouse model of infection, we demonstrate here that STAB-1 controls Lm-induced cytokine and chemokine production and immune cell accumulation in Lm-infected organs. We show that STAB-1 also regulates the recruitment of myeloid cells in response to Lm infection and contributes to clear circulating bacteria. In addition, whereas STAB-1 appears to promote bacterial uptake by macrophages, infection by pathogenic Listeria induces the down regulation of STAB-1 expression and its delocalization from the host cell membrane.

We propose STAB-1 as a new SR involved in the control of Lm infection through the regulation of host defense mechanisms, a process that would be targeted by bacterial virulence factors to promote infection.

Preparation and characterization of itraconazole loaded nanomicelles based on dextran-behenic acid for cutaneous leishmaniasis treatment

Cutaneous leishmaniasis is known as the most prevalent clinical form of leishmaniasis. It needs the development of new therapies due to the serious side-effects promoted by taking the current drugs. In the present study, dextran-behenic acid (DEX-BA) based nanomicelles were developed to direct the delivery of itraconazole (ITZ) to the macrophages and enhance its toxic effects against Leishmania parasites. DEX-BA was synthesized through the esterification of dextran with behenic acid. The critical micelle concentration of the newly developed conjugate was evaluated using pyrene as the fluorescent probe. The nanomicelles were generated by the dialysis method; then they were optimized by applying a Box-Behnken design. The effects of the dialysis temperature, polymer content, and sonication time on the characteristics of micelles were subsequently studied. Furthermore, in vitro efficacy against Leishmania major promastigotes and parasite-infected macrophages was evaluated. The optimized formulation showed the particle size of 195.16 ± 3.06 nm, the polydispersity index of 0.39 ± 0.01, the zeta potential of -16.29 ± 0.89 mV, the encapsulation efficiency % of 56.11 ± 4.9, and the release efficiency % of 51.29 ± 1.97. According to scanning electron microscopy, the nanomicelles were found to be nearly spherical in shape. ITZ-loaded nanomicelles showed the strongest anti-leishmanial activities when compared with the free ITZ and drug-free nanomicelles. It could be, therefore, concluded that ITZ-loaded nanomicelles might be useful as an alternative therapy for the treatment of cutaneous leishmania.

Deciphering the Role Played by Autophagy in Leishmania Infection

In recent decades, studies have shown that, depending on parasite species and host background, autophagy can either favor infection or promote parasite clearance. To date, relatively few studies have attempted to assess the role played by autophagy in Leishmania infection. While it has been consistently shown that Leishmania spp. induce autophagy in a variety of cell types, published results regarding the effects of autophagic modulation on Leishmania survival are contradictory. The present review, after a short overview of the general aspects of autophagy, aims to summarize the current body of knowledge surrounding how Leishmania spp. adaptively interact with macrophages, the host cells mainly involved in controlling leishmaniasis. We then explore the scarce studies that have investigated interactions between these parasite species and the autophagic pathway, and finally present a critical perspective on how autophagy influences infection outcome.

The ectodomains of the lymphocyte scavenger receptors CD5 and CD6 interact with tegumental antigens from Echinococcus granulosus sensu lato and protect mice against secondary cystic echinococcosis

Background

Scavenger Receptors (SRs) from the host’s innate immune system are known to bind multiple ligands to promote the removal of non-self or altered-self targets. CD5 and CD6 are two highly homologous class I SRs mainly expressed on all T cells and the B1a cell subset, and involved in the fine tuning of activation and differentiation signals delivered by the antigen-specific receptors (TCR and BCR, respectively), to which they physically associate. Additionally, CD5 and CD6 have been shown to interact with and sense the presence of conserved pathogen-associated structures from bacteria, fungi and/or viruses.

Methodology/Principal findings

We report herein the interaction of CD5 and CD6 lymphocyte surface receptors with Echinococcus granulosus sensu lato (s.l.). Binding studies show that both soluble and membrane-bound forms of CD5 and CD6 bind to intact viable protoscoleces from E. granulosus s.l. through recognition of metaperiodate-resistant tegumental components. Proteomic analyses allowed identification of thioredoxin peroxidase for CD5, and peptidyl-prolyl cis-trans isomerase (cyclophilin) and endophilin B1 (antigen P-29) for CD6, as their potential interactors. Further in vitro assays demonstrate that membrane-bound or soluble CD5 and CD6 forms differentially modulate the pro- and anti-inflammatory cytokine release induced following peritoneal cells exposure to E. granulosus s.l. tegumental components. Importantly, prophylactic infusion of soluble CD5 or CD6 significantly ameliorated the infection outcome in the mouse model of secondary cystic echinococcosis.

Conclusions/Significance

Taken together, the results expand the pathogen binding properties of CD5 and CD6 and provide novel evidence for their therapeutic potential in human cystic echinococcosis.

Scavenger Receptors (SRs) are constituents of host’s innate immune system able to sense and remove altered-self and/or pathogen components. Data on their interaction with helminth parasites is scarce. In this work, we describe that CD5 and CD6 -two lymphoid SRs previously reported to interact with conserved structures from bacteria, fungi and viruses- recognize tegumental components in the cestode parasite Echinococcus granulosus sensu lato (s.l.). Moreover, both receptors differentially modulate the cytokine release by host cells exposed to E. granulosus s.l. tegumental components. Importantly, the infusion of soluble forms of CD5 or CD6 improve infection outcomes in a murine model of secondary cystic echinococcosis. In summary, our results expand the pathogen binding properties of CD5 and CD6 and suggest their therapeutic potential against helminth infections.

Scavenger Receptors: Promiscuous Players during Microbial Pathogenesis

Innate immunity is the most broadly effective host defense, being essential to clear the majority of microbial infections. Scavenger Receptors comprise a family of sensors expressed in a multitude of host cells, whose dual role during microbial pathogenesis gained importance over recent years. SRs regulate the recruitment of immune cells and control both host inflammatory response and bacterial load. In turn, pathogens have evolved different strategies to overcome immune response, avoid recognition by SRs and exploit them to favor infection. Here, we discuss the most relevant findings regarding the interplay between SRs and pathogens, discussing how these multifunctional proteins recognize a panoply of ligands and act as bacterial phagocytic receptors.

Exploitation of Scavenger Receptor, Macrophage Receptor with Collagenous Structure, by Cryptococcus neoformans Promotes Alternative Activation of Pulmonary Lymph Node CD11b+ Conventional Dendritic Cells and Non-Protective Th2 Bias

Macrophage receptor with collagenous structure (MARCO) contributes to fungal containment during the early/innate phase of cryptococcal infection; however, its role in adaptive antifungal immunity remains unknown. Using a murine model of cryptococcosis, we compared host adaptive immune responses in wild-type and MARCO^−/− mice throughout an extended time course post-infection. Unlike in early infection, MARCO deficiency resulted in improved pulmonary fungal clearance and diminished cryptococcal dissemination during the efferent phase. Improved fungal control in the absence of MARCO expression was associated with enhanced hallmarks of protective Th1-immunity, including higher frequency of pulmonary TNF-α-producing T cells, increased cryptococcal-antigen-triggered IFN-γ and TNF-α production by splenocytes, and enhanced expression of M1 polarization genes by pulmonary macrophages. Concurrently, we found lower frequencies of IL-5- and IL-13-producing T cells in the lungs, impaired production of IL-4 and IL-10 by cryptococcal antigen-pulsed splenocytes, and diminished serum IgE, which were hallmarks of profoundly suppressed efferent Th2 responses in MARCO-deficient mice compared to WT mice. Mechanistically, we found that MARCO expression facilitated early accumulation and alternative activation of CD11b⁺ conventional DC (cDC) in the lung-associated lymph nodes (LALNs), which contributed to the progressive shift of the immune response from Th1 toward Th2 at the priming site (LALNs) and local infection site (lungs) during the efferent phase of cryptococcal infection. Taken together, our study shows that MARCO can be exploited by the fungal pathogen to promote accumulation and alternative activation of CD11b⁺ cDC in the LALN, which in turn alters Th1/Th2 balance to promote fungal persistence and dissemination.

Scavenger Receptor MARCO Orchestrates Early Defenses and Contributes to Fungal Containment during Cryptococcal Infection

The scavenger receptor macrophage receptor with collagenous structure (MARCO) promotes protective innate immunity against bacterial and parasitic infections; however, its role in host immunity against fungal pathogens, including the major human opportunistic fungal pathogen Cryptococcus neoformans, remains unknown. Using a mouse model of C. neoformans infection, we demonstrated that MARCO deficiency leads to impaired fungal control during the afferent phase of cryptococcal infection. Diminished fungal containment in MARCO^-/- mice was accompanied by impaired recruitment of Ly6C^high monocytes and monocyte-derived dendritic cells (moDC) and lower moDC costimulatory maturation. The reduced recruitment and activation of mononuclear phagocytes in MARCO^-/- mice was linked to diminished early expression of IFN-γ along with profound suppression of CCL2 and CCL7 chemokines, providing evidence for roles of MARCO in activation of the CCR2 axis during C. neoformans infection. Lastly, we found that MARCO was involved in C. neoformans phagocytosis by resident pulmonary macrophages and DC. We conclude that MARCO facilitates early interactions between C. neoformans and lung-resident cells and promotes the production of CCR2 ligands. In turn, this contributes to a more robust recruitment and activation of moDC that opposes rapid fungal expansion during the afferent phase of cryptococcal infection.

Leishmania amazonensis fails to induce the release of reactive oxygen intermediates by CBA macrophages

CBA mouse macrophages effectively control Leishmania major infection, yet are permissive to Leishmania amazonensis. It has been established that some Leishmania species are destroyed by reactive oxygen species (ROS). However, other species of Leishmania exhibit resistance to ROS or even down-modulate ROS production. We hypothesized that L. amazonensis–infected macrophages reduce ROS production soon after parasite–cell interaction. Employing a highly sensitive analysis technique based on chemiluminescence, the production of superoxide () and hydrogen peroxide (H₂O₂) by L. major- or L. amazonensis-infected CBA macrophages were measured. L. major induces macrophages to release levels of 3·5 times higher than in uninfected cells. This production is partially dependent on NADPH oxidase (NOX) type 2. The level of accumulated H₂O₂ is 20 times higher in L. major-than in L. amazonensis-infected cells. Furthermore, macrophages stimulated with L. amazonensis release amounts of ROS similar to uninfected cells. These findings support previous studies showing that CBA macrophages are effective in controlling L. major infection by a mechanism dependent on both production and H₂O₂ generation. Furthermore, these data reinforce the notion that L. amazonensis survive inside CBA macrophages by reducing ROS production during the phagocytic process.

Exclusion of synaptotagmin V at the phagocytic cup by Leishmania donovani lipophosphoglycan results in decreased promastigote internalization

Regulators of membrane fusion play an important role in phagocytosis, as they regulate the focal delivery of endomembrane that is required for optimal internalization of large particles. During internalization of Leishmania promastigotes, the surface glycolipid lipophosphoglycan (LPG) is transferred to the macrophage membrane and modifies its fusogenic properties. In this study, we investigated the impact of LPG on the recruitment of the exocytosis regulator synaptotagmin V (Syt V) at the area of internalization and on the early steps of phagocytosis. Using Leishmania donovani LPG-defective mutants and LPG-coated particles, we established that LPG reduces the phagocytic capacity of macrophages and showed that it causes exclusion of Syt V from the nascent phagosome. Silencing of Syt V inhibited phagocytosis to the same extent as LPG, and these effects were not cumulative, consistent with a Syt V-dependent mechanism for the inhibition of phagocytosis by LPG. Previous work has revealed that LPG-mediated exclusion of Syt V from phagosomes prevents the recruitment of the vacuolar ATPase and acidification. Thus, whereas exclusion of Syt V from phagosomes in the process of formation may be beneficial for the creation of a hospitable intracellular niche, it reduces the phagocytic capacity of macrophages. We propose that the cost associated with a reduced internalization rate may be compensated by increased survival, and could lead to a greater overall parasite fitness.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

Major surface protease of trypanosomatids: one size fits all?

Major surface protease (MSP or GP63) is the most abundant glycoprotein localized to the plasma membrane of Leishmania promastigotes. MSP plays several important roles in the pathogenesis of leishmaniasis, including but not limited to (i) evasion of complement-mediated lysis, (ii) facilitation of macrophage (Mø) phagocytosis of promastigotes, (iii) interaction with the extracellular matrix, (iv) inhibition of natural killer cellular functions, (v) resistance to antimicrobial peptide killing, (vi) degradation of Mø and fibroblast cytosolic proteins, and (vii) promotion of survival of intracellular amastigotes. MSP homologues have been found in all other trypanosomatids studied to date including heteroxenous members of Trypanosoma cruzi, the extracellular Trypanosoma brucei, unusual intraerythrocytic Endotrypanum spp., phytoparasitic Phytomonas spp., and numerous monoxenous species. These proteins are likely to perform roles different from those described for Leishmania spp. Multiple MSPs in individual cells may play distinct roles at some time points in trypanosomatid life cycles and collaborative or redundant roles at others. The cellular locations and the extracellular release of MSPs are also discussed in connection with MSP functions in leishmanial promastigotes.