Mutual regulations between Toxoplasma gondii and type I interferon

In the decades since the discovery, Type I interferon (IFN-I) has been intensively studied for their antiviral activity. However, increasing evidences suggest that it may also play an important role in the infection of Toxoplasma gondii, a model organism for intracellular parasites. Recent studies demonstrated that the induction of IFN-I by the parasite depends on cell type, strain genotype, and mouse strain. IFN-I can inhibit the proliferation of T. gondii, but few studies showed that it is beneficial to the growth of the parasite. Meanwhile, T. gondii also can secrete proteins that impact the pathway of IFN-I production and downstream induced interferon-stimulated genes (ISGs) regulation, thereby escaping immune destruction by the host. This article reviews the major findings and progress in the production, function, and regulation of IFN-I during T. gondii infection, to thoroughly understand the innate immune mechanism of T. gondii infection, which provides a new target for subsequent intervention and treatment.

Transcriptional changes associated with apoptosis and Type I IFN underlie the early interaction between Besnoitia besnoiti tachyzoites and monocyte-derived macrophages

Besnoitia besnoiti-infected bulls may develop severe systemic clinical signs and orchitis that may ultimately cause sterility during the acute infection. Macrophages might play a relevant role in pathogenesis of the disease and the immune response raised against B. besnoiti infection. This study aimed to dissect the early interaction between B. besnoiti tachyzoites and primary bovine monocyte-derived macrophages in vitro. First, the B. besnoiti tachyzoite lytic cycle was characterized. Next, dual transcriptomic profiling of B. besnoiti tachyzoites and macrophages was conducted at early infection (4 h and 8 h p.i. by high-throughput RNA sequencing. Macrophages inoculated with heat-killed tachyzoites (MO-hkBb) and non-infected macrophages (MO) were used as controls. Besnoitia besnoiti was able to invade and proliferate in macrophages. Upon infection, macrophage activation was demonstrated by morphological and transcriptomic changes. Infected macrophages were smaller, round and lacked filopodial structures, which might be associated with a migratory phenotype demonstrated in other apicomplexan parasites. The number of differentially expressed genes (DEGs) increased substantially during infection. In B. besnoiti-infected macrophages (MO-Bb), apoptosis and mitogen-activated protein kinase (MAPK) pathways were regulated at 4 h p.i., and apoptosis was confirmed by TUNEL assay. The Herpes simplex virus 1 infection pathway was the only significantly enriched pathway in MO-Bb at 8 h p.i. Relevant DEGs of the Herpes simplex virus 1 infection (IFNα) and the apoptosis pathways (CHOP-2) were also significantly regulated in the testicular parenchyma of naturally infected bulls. Furthermore, the parasite transcriptomic analysis revealed DEGs mainly related to host cell invasion and metabolism. These results provide a deep overview of the earliest macrophage modulation by B. besnoiti that may favour parasite survival and proliferation in a specialized phagocytic immune cell. Putative parasite effectors were also identified.

Function and regulation of cGAS-STING signaling in infectious diseases

The efficacious detection of pathogens and prompt induction of innate immune signaling serve as a crucial component of immune defense against infectious pathogens. Over the past decade, DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signaling adaptor stimulator of interferon genes (STING) have emerged as key mediators of type I interferon (IFN) and nuclear factor-κB (NF-κB) responses in health and infection diseases. Moreover, both cGAS-STING pathway and pathogens have developed delicate strategies to resist each other for their survival. The mechanistic and functional comprehension of the interplay between cGAS-STING pathway and pathogens is opening the way for the development and application of pharmacological agonists and antagonists in the treatment of infectious diseases. Here, we briefly review the current knowledge of DNA sensing through the cGAS-STING pathway, and emphatically highlight the potent undertaking of cGAS-STING signaling pathway in the host against infectious pathogenic organisms.