Clostridium difficile (C. difficile) is the main cause of antibiotic-associated diarrhea prevailing in hospital settings. In the past decade, the morbidity and mortality of C. difficile infection (CDI) has increased significantly due to the emergence of hypervirulent strains. Toxin A (TcdA) and toxin B (TcdB), the two exotoxins of C. difficile, are the major virulence factors of CDI. The common mode of action of TcdA and TcdB is elicited by specific glucosylation of Rho-GTPase proteins in the host cytosol using UDP-glucose as a co-substrate, resulting in the inactivation of Rho proteins. Rho proteins are the key members in many biological processes and signaling pathways, inactivation of which leads to cytopathic and cytotoxic effects and immune responses of the host cells. It is supposed that Rho GTPases play an important role in the toxicity of C. difficile toxins. This review focuses on recent progresses in the understanding of functional consequences of Rho GTPases glucosylation induced by C. difficile toxins and the role of Rho GTPases in the toxicity of TcdA and TcdB.

The second human pegivirus (HPgV-2) is a virus discovered in the plasma of a hepatitis C virus (HCV)-infected patient in 2015 belonging to the pegiviruses of the family Flaviviridae. HPgV-2 has been proved to be epidemiologically associated with and structurally similar to HCV but unrelated to HCV disease and non-pathogenic, but its natural history and tissue tropism remain unclear. HPgV-2 is a unique RNA virus sharing the features of HCV and the first human pegivirus (HPgV-1 or GBV-C). Moreover, distinct from most RNA viruses such as HCV, HPgV-1 and human immunodeficiency virus (HIV), HPgV-2 exhibits much lower genomic diversity, with a high global sequence identity ranging from 93.5 to 97.5% and significantly lower intra-host variation than HCV. The mechanisms underlying the conservation of the HPgV-2 genome are not clear but may include efficient innate immune responses, low immune selection pressure and, possibly, the unique features of the viral RNA-dependent RNA polymerase (RdRP). In this review, we summarize the prevalence, pathogenicity and genetic diversity of HPgV-2 and discuss the possible reasons for the uniformity of its genome sequence, which should elucidate the implications of RNA virus fidelity for attenuated viral vaccines.

Clostridium difficile toxin A (TcdA) and toxin B (TcdB) are the major virulence factors involved in C. difficile-associated diarrhea and pseudomembranous colitis. TcdA and TcdB both contain at least four distinct domains: the glucosyltransferase domain, cysteine protease domain, receptor binding domain, and translocation domain. Few studies have investigated the translocation domain and its mechanism of action. Recently, it was demonstrated that a segment of 97 amino acids (AA 1756–1852, designated D97) within the translocation domain of TcdB is essential for the in vitro and in vivo toxicity of TcdB. However, the mechanism by which D97 regulates the action of TcdB in host cells and the important amino acids within this region are unknown. In this study, we discovered that a smaller fragment, amino acids 1756–1780, located in the N-terminus of the D97 fragment, is essential for translocation of the effector glucosyltransferase domain into the host cytosol. A sequence of 25AA within D97 is predicted to form an alpha helical structure and is the critical part of D97. The deletion mutant TcdB_{∆1756–1780} showed similar glucosyltransferase and cysteine protease activity, cellular binding, and pore formation to wild type TcdB, but it failed to induce the glucosylation of Rho GTPase Rac1 of host cells. Moreover, we found that TcdB_{∆1756–1780} was rapidly degraded in the endosome of target cells, and therefore its intact glucosyltransferase domain was unable to translocate efficiently into host cytosol. Our finding provides an insight into the molecular mechanisms of action of TcdB in the intoxication of host cells.

Syphilis is a chronic, systemic sexually transmitted disease (STD) caused by the Treponema pallidum (T. pallidum). It is one of the most prevalent STDs in the world. In the United State, the cases ...

Objective: The immunological mechanisms underlying the syphilis serofast remain incompletely elucidated. This systematic review and meta-analysis aims to quantify the association between key immune indicators and serofast. Methods: We systematically searched PubMed, Embase, Web of Science, Google Scholar and Chinese databases (CNKI, VIP, and CBMdisc) until December 31, 2024, for case-control, cross-sectional or cohort studies meeting serofast criteria (RPR/TRUST titer ≤1:8 persisting for ≥12 months). Random-effects models were used to calculate standardized mean differences (SMD) with 95% confidence intervals (CIs). The risk of bias was assessed using the Newcastle-Ottawa Scale (for observational studies) by two independent reviewers. Results: A total of 38 studies involving 5082 patients were included. The serofast group exhibited significant immune dysregulation: (1) Cellular immune suppression:decreased CD4+ T cells (SMD=-0.61, I²=33.5%) and increased CD8+ T cells (SMD = 0.40, I²=66.7%), leading to an inverted CD4+/CD8+ ratio (SMD=-0.44, I²=64.7%); (2) Th1/Th2 shift:suppression of Th1 cytokines (e.g., IFN-γ, SMD=-2.19, I²=95.7%) with a predominant Th2 response (e.g., IL-10, SMD =+ 2.63,I²=92.5%); (3) Humoral abnormalities: persistently elevated IgM (SMD = 0.96,I²=94.4%) and complement consumption (C3,SMD=-0.60, I²=89.0%; C4, SMD=-0.80, I²=87.6%); (4) Signaling dysregulation: downregulated TLR2 expression and disordered chemokine receptors (TLR2 mRNA,SMD=-1.52, I²=36.0%).The substantial heterogeneity (I² > 50%) observed in several analyses was explored in subgroup and sensitivity analyses, as detailed in the main text. Conclusions: The serofast is characterized by a cascade of “cellular immune suppression-Th1/Th2 shift-complement exhaustion.” Our findings establish a quantified immunological basis for the serofast state and suggest potential targets for immunomodulatory therapy. Systematic review registration: https://www.crd.york.ac.uk/prospero/ , identifier CRD420251156478.