Unique roles of co-receptor-bound LCK in helper and cytotoxic T cells.

The kinase LCK and CD4/CD8 co-receptors are crucial components of the T cell antigen receptor (TCR) signaling machinery, leading to key T cell fate decisions. Despite decades of research, the roles of CD4-LCK and CD8-LCK interactions in TCR triggering in vivo remain unknown. In this study, we created animal models expressing endogenous levels of modified LCK to resolve whether and how co-receptor-bound LCK drives TCR signaling. We demonstrated that the role of LCK depends on the co-receptor to which it is bound. The CD8-bound LCK is largely dispensable for antiviral and antitumor activity of cytotoxic T cells in mice; however, it facilitates CD8+ T cell responses to suboptimal antigens in a kinase-dependent manner. By contrast, the CD4-bound LCK is required for efficient development and function of helper T cells via a kinase-independent stabilization of surface CD4. Overall, our findings reveal the role of co-receptor-bound LCK in T cell biology, show that CD4- and CD8-bound LCK drive T cell development and effector immune responses using qualitatively different mechanisms and identify the co-receptor-LCK interactions as promising targets for immunomodulation.

ABIN1 is a negative regulator of effector functions in cytotoxic T cells.

T cells are pivotal in the adaptive immune defense, necessitating a delicate balance between robust response against infections and self-tolerance. Their activation involves intricate cross-talk among signaling pathways triggered by the T-cell antigen receptors (TCR) and co-stimulatory or inhibitory receptors. The molecular regulation of these complex signaling networks is still incompletely understood. Here, we identify the adaptor protein ABIN1 as a component of the signaling complexes of GITR and OX40 co-stimulation receptors. T cells lacking ABIN1 are hyper-responsive ex vivo, exhibit enhanced responses to cognate infections, and superior ability to induce experimental autoimmune diabetes in mice. ABIN1 negatively regulates p38 kinase activation and late NF-κB target genes. P38 is at least partially responsible for the upregulation of the key effector proteins IFNG and GZMB in ABIN1-deficient T cells after TCR stimulation. Our findings reveal the intricate role of ABIN1 in T-cell regulation.

Deubiquitinase BAP1 is crucial for surface expression of T cell receptor (TCR) complex, T cell-B cell conjugate formation, and T cell activation.

The adaptive immune response critically hinges on the functionality of T cell receptors (TCRs), governed by complex molecular mechanisms, including ubiquitination. In this study, we delved into the role of deubiquitinases (DUBs) in T cell immunity, focusing on T cell-B cell conjugate formation and T cell activation. Using a CRISPR-Cas9 screening approach targeting DUB genes in Jurkat T cells, we identified BAP1 as a key positive regulator of T cell-B cell conjugate formation. Subsequent investigations into BAP1 knockout cells revealed impaired T cell activation, evidenced by decreased MAPK and NF-kB signaling pathways and reduced CD69 expression upon TCR stimulation. Flow cytometry and qPCR analyses demonstrated that BAP1 deficiency leads to decreased surface expression of TCR complex components and reduced mRNA levels of the co-stimulatory molecule CD28. Notably, the observed phenotypes associated with BAP1 knockout are specific to T cells and fully dependent on BAP1 catalytic activity. In-depth RNA-seq and mass spectrometry analyses further revealed that BAP1 deficiency induces broad mRNA and protein expression changes. Overall, our findings elucidate the vital role of BAP1 in T cell biology, especially in T cell-B cell conjugate formation and T cell activation, offering new insights and directions for future research in immune regulation.

The diagnostic value of the droplet digital PCR for the detection of bovine deltapapillomavirus in goats by liquid biopsy.

In the present study, the highly pathogenic bovine deltapapillomavirus (δPV) was investigated by liquid biopsy in blood samples of 168 clinically normal goats using both droplet digital PCR (ddPCR) and quantitative real-time PCR (qPCR). Overall, ddPCR discovered BPV E5 DNA in ~ 61.3% of the blood samples examined, while real-time qPCR revealed the virus in ~ 10.7% of the same samples. Moreover, ddPCR showed BPV E5 DNA in ~ 78.8% of blood samples from goats that were in close contact with cattle and in 20% of blood samples from goats living in closed pens without any contact with cattle. In addition, ddPCR unmasked a single BPV genotype in ~ 59.2% and multiple genotypes in ~ 40.8% of goats harbouring BPV DNA, while real-time qPCR detected single genotypes in ~ 17% and multiple genotypes in ~ 1%. Of the BPV co-infections detected by ddPCR, 28 (~67%) involved two genotypes, eight (~19%) three genotypes and six (~14%) four genotypes. In contrast, real-time qPCR revealed BPV co-infection by two genotypes in only one sample and failed to detect co-infection by three or four genotypes. BPV2 and BPV13 were the most prevalent viruses responsible for single and multiple co-infections, respectively. The present study showed that ddPCR is promising method for circulating bovine papillomavirus DNA detection and quantification and suggested that animal husbandry practices contribute to cross-species transmission of BPVs.

Bovine Delta Papillomavirus E5 Oncoprotein Interacts With TRIM25 and Hampers Antiviral Innate Immune Response Mediated by RIG-I-Like Receptors.

Persistent infection and tumourigenesis by papillomaviruses (PVs) require viral manipulation of various of cellular processes, including those involved in innate immune responses. Herein, we showed that bovine PV (BPV) E5 oncoprotein interacts with a tripartite motif-containing 25 (TRIM25) but not with Riplet in spontaneous BPV infection of urothelial cells of cattle. Statistically significant reduced protein levels of TRIM25, retinoic acid-inducible gene I (RIG-I), and melanoma differentiation-associated gene 5 (MDA5) were detected by Western blot analysis. Real-time quantitative PCR revealed marked transcriptional downregulation of RIG-I and MDA5 in E5-expressing cells compared with healthy urothelial cells. Mitochondrial antiviral signalling (MAVS) protein expression did not vary significantly between diseased and healthy cells. Co-immunoprecipitation studies showed that MAVS interacted with a protein network composed of Sec13, which is a positive regulator of MAVS-mediated RLR antiviral signalling, phosphorylated TANK binding kinase 1 (TBK1), and phosphorylated interferon regulatory factor 3 (IRF3). Immunoblotting revealed significantly low expression levels of Sec13 in BPV-infected cells. Low levels of Sec13 resulted in a weaker host antiviral immune response, as it attenuates MAVS-mediated IRF3 activation. Furthermore, western blot analysis revealed significantly reduced expression levels of pTBK1, which plays an essential role in the activation and phosphorylation of IRF3, a prerequisite for the latter to enter the nucleus to activate type 1 IFN genes. Our results suggested that the innate immune signalling pathway mediated by RIG-I-like receptors (RLRs) was impaired in cells infected with BPVs. Therefore, an effective immune response is not elicited against these viruses, which facilitates persistent viral infection.