Leishmania kinetoplast DNA contributes to parasite burden in infected macrophages: Critical role of the cGAS-STING-TBK1 signaling pathway in macrophage parasitemia

Memory T cells: promising biomarkers for evaluating protection and vaccine efficacy against leishmaniasis

Understanding the immune response to Leishmania infection and identifying biomarkers that correlate with protection are crucial for developing effective vaccines. One intriguing aspect of Leishmania infection is the persistence of parasites, even after apparent lesion healing. Various host cells, including dendritic cells, fibroblasts, and Langerhans cells, may serve as safe sites for latent infection. Memory T cells, especially tissue-resident memory T cells (TRM), play a crucial role in concomitant immunity against cutaneous Leishmania infections. These TRM cells are long-lasting and can protect against reinfection in the absence of persistent parasites. CD4+ TRM cells, in particular, have been implicated in protection against Leishmania infections. These cells are characterized by their ability to reside in the skin and rapidly respond to secondary infections by producing cytokines such as IFN-γ, which activates macrophages to kill parasites. The induction of CD4+ TRM cells has shown promise in experimental immunization, leading to protection against Leishmania challenge infections. Identifying biomarkers of protection is a critical step in vaccine development and CD4+ TRM cells hold potential as biomarkers, as their presence and functions may correlate with protection. While recent studies have shown that Leishmania-specific memory CD4+ T-cell subsets are present in individuals with a history of cutaneous leishmaniasis, further studies are needed to characterize CD4+ TRM cell populations. Overall, this review highlights the importance of memory T cells, particularly skin-resident CD4+ TRM cells, as promising targets for developing effective vaccines against leishmaniasis and as biomarkers of immune protection to assess the efficacy of candidate vaccines against human leishmaniasis.

cGAS-STING Pathway Activation during Trypanosoma cruzi Infection Leads to Tissue-Dependent Parasite Control

Host cell invasion by Trypanosoma cruzi is a markedly silent process, with limited host transcriptional changes indicative of innate immune recognition, except for a modest type I IFN (IFN-I) response. In this study, we show that T. cruzi-induced IFN-β production was nearly abolished in primary murine cGAS-/- or stimulator of IFN genes (STING)-deficient (STINGGt) macrophages and fibroblasts. T. cruzi infection did not impact the ability of IFN-regulatory factor reporter macrophages to respond to classical cGAS-STING agonists, indicating that the limited IFN-β induction is not due to active parasite suppression. cGAS-/-, STINGGt, and IFN-α/β receptor-/- (IFNAR-/-) macrophages infected with T. cruzi yielded significantly higher numbers of amastigotes compared with wild-type macrophages; however, the impact of the STING pathway during infection in vivo is more complex. Despite an initial increase in parasite growth, STINGGt and IFNAR-/- mice ultimately had lower parasite burden in footpads as compared with wild-type mice, demonstrating a role for IFN-I expression in potentiating parasite growth at the infection site. STING pathway activation had little impact on parasite levels in the skeletal muscle; however, in the heart, cGAS-/- and STINGGt mice, but not IFNAR-/- mice, accumulated higher acute parasite loads, suggesting a protective role of STING sensing of T. cruzi in this organ that was independent of IFN-I. Together, these results demonstrate that host cGAS-STING senses T. cruzi infection, enhancing parasite growth at the site of entry, and contributes to acute-phase parasite restriction in the heart, a major site of tissue damage in chronic T. cruzi infection.

cGAS-STING signaling pathway in intestinal homeostasis and diseases

The intestinal mucosa is constantly exposed to commensal microbes, opportunistic pathogens, toxins, luminal components and other environmental stimuli. The intestinal mucosa consists of multiple differentiated cellular and extracellular components that form a critical barrier, but is also equipped for efficient absorption of nutrients. Combination of genetic susceptibility and environmental factors are known as critical components involved in the pathogenesis of intestinal diseases. The innate immune system plays a critical role in the recognition and elimination of potential threats by detecting pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). This host defense is facilitated by pattern recognition receptors (PRRs), in which the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has gained attention due to its role in sensing host and foreign double-stranded DNA (dsDNA) as well as cyclic dinucleotides (CDNs) produced by bacteria. Upon binding with dsDNA, cGAS converts ATP and GTP to cyclic GMP-AMP (cGAMP), which binds to STING and activates TANK binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3), inducing type I interferon (IFN) and nuclear factor kappa B (NF-κB)-mediated pro-inflammatory cytokines, which have diverse effects on innate and adaptive immune cells and intestinal epithelial cells (IECs). However, opposite perspectives exist regarding the role of the cGAS-STING pathway in different intestinal diseases. Activation of cGAS-STING signaling is associated with worse clinical outcomes in inflammation-associated diseases, while it also plays a critical role in protection against tumorigenesis and certain infections. Therefore, understanding the context-dependent mechanisms of the cGAS-STING pathway in the physiopathology of the intestinal mucosa is crucial for developing therapeutic strategies targeting the cGAS-STING pathway. This review aims to provide insight into recent findings of the protective and detrimental roles of the cGAS-STING pathway in intestinal diseases.

Aflatoxin B1 Induced Oxidative Stress and Gut Microbiota Disorder to Increase the Infection of Cyprinid Herpesvirus 2 in Gibel Carp (Carassius auratus gibelio)

Aflatoxin contamination of food and water is a serious problem worldwide. This study investigated the defensive ability of gibel carp exposed to aflatoxin B1 (AFB1) by challenging it with cyprinid herpesvirus 2 (CyHV-2) infection. The data showed that AFB1 exposure significantly increased the mortality of CyHV-2-infected gibel carp, and enhanced the viral load in the fish liver, kidney, and spleen. The oxidative-antioxidant balance suggested that AFB1 induced severe oxidative stress, including increased reactive oxygen species (ROS) and malondialdehyde (MDA) levels in the AFB1 exposed group, and the reduced activity of superoxide dismutase (SOD), glutathione-S-transferase (GST) and catalase (CAT) in the AFB1 exposed group. Meanwhile, the related expression of nuclear factor erythroid 2-related factor 2 (Nrf2), interferon regulatory factor 3 (IRF3) and the type 1 interferon (IFN1) were noticeably down-regulated, but caspase-1 was up-regulated, after exposure to AFB1, demonstrating that fish are unable to avoid the virus infection. It should be noted that the intestinal microbiota diversity and richness were lower in the AFB1 exposed group, and the composition of intestinal microbiota was affected by AFB1, resulting in the higher abundance of bacteria (such as Aeromonas and Bacteroides) and the lower abundance of potentially beneficial bacteria (such as Cetobacterium and Clostridium) in the AFB1 exposed group. This research provides insight into the possibility that AFB1 may increase the susceptibility of C. gibelio to CyHV-2 infection, and thus amplify the viral outbreak to endanger ecological safety in aquatic environment.