Downregulation of CD73 on CD4+ T cells from patients with chronic Chikungunya infection

Altered CD73-Adenosine Signaling Linked to Infection in Patients undergoing hemodialysis

Purpose

Infection is the most common cause of hospitalization and the second most common cause of mortality among patients undergoing hemodialysis (HD). The enzyme CD73, a cell surface 5'-nucleotidase, regulates the balance between pro-inflammatory nucleotides and anti-inflammatory adenosine. Diminished CD73-adenosine signaling contributes to severe infections.

Methods

In this prospective cohort study, 393 patients who underwent HD for over six months were evaluated for CD73+Tcell ratios and were followed up for three years to track infection events. Kaplan-Meier curves and Cox regression analyses were used to evaluate the relationship between CD73+T cells and infections; meanwhile, multiple logistic regression analysis was used to analyze differences among infection groups. In addition, a 5/6 nephrectomy (5/6 Nx) rat model and cecal ligation and puncture (CLP) were used to verify the effect of chronic kidney disease (CKD) and sepsis on CD73-adenosine signaling.

Results

Decreased CD73+ T cells were independently associated with increased infection risk over one and three years. The hazard ratios for one- and three-year infection incidences were 3.173 (95% CI 1.782-5.650, p < 0.001) and 1.429 (95% CI 1.052-1.992, p = 0.035), respectively. Furthermore, they were associated with recurrent and fatal severe infections. Animal models demonstrated reduced CD73 mRNA transcript and adenosine receptor levels, along with decreased serum adenosine levels in CKD. Impairment of CD73-adenosine signaling was more pronounced after CLP in CKD rats.

Conclusion

Lower CD73+T cell levels are strongly associated with infection complications in patients undergoing HD. Altered CD73-adenosine signaling likely plays a substantial role in immune dysfunction in CKD.

CD73 as a T cell dysfunction marker predicting cardiovascular and infection events in patients undergoing hemodialysis

BACKGROUND

T cell dysfunction observed in patients undergoing hemodialysis (HD) has been linked to an extremely high morbidity of cardiovascular events (CVEs) and infections. The cell-surface 5'-nucleotidase CD73 sets the balance between pro-inflammatory nucleotides and anti-inflammatory adenosine.

METHODS

A total of 395 patients who had been receiving HD for at least six months were evaluated for proportions of CD73+ cells in both the CD4+ T cell and CD8+ T cell compartment and followed for one year to document CVEs and infections. Differences in the proportions of CD73-expressingT cells between healthy controls and patients undergoing HD were compared. The relationship between CD73+ T cells and clinical outcomes was analyzed using the Kaplan-Meier curve and Cox regression.

RESULTS

HD was significantly related to a lower fraction of CD4+CD73+ T cells. In patients on HD, lower proportions of CD4+ CD73+T cells and CD8+ CD73+T cells were both associated with systemic inflammation and T cell terminal differentiation. More importantly, a lower CD4+CD73+T cell ratio independently predicted CVEs and infection in these patients.

CONCLUSION

We identified CD73 as a T cell dysfunction marker predicting cardiovascular and infection events in patients undergoing HD, which provides a potential target in future studies of uremia-related immune dysfunction.

Elevated CD39+T-Regulatory Cells and Reduced Levels of Adenosine Indicate a Role for Tolerogenic Signals in the Progression from Moderate to Severe COVID-19

Viral infections trigger inflammation by controlling ATP release. CD39 ectoenzymes hydrolyze ATP/ADP to AMP, which is converted by CD73 into anti-inflammatory adenosine (ADO). ADO is an anti-inflammatory and immunosuppressant molecule which can enhance viral persistence and severity. The CD39-CD73-adenosine axis contributes to the immunosuppressive T-reg microenvironment and may affect COVID-19 disease progression. Here, we investigated the link between CD39 expression, mostly on T-regs, and levels of CD73, adenosine, and adenosine receptors with COVID-19 severity and progression. Our study included 73 hospitalized COVID-19 patients, of which 33 were moderately affected and 40 suffered from severe infection. A flow cytometric analysis was used to analyze the frequency of T-regulatory cells (T-regs), CD39+ T-regs, and CD39+CD4+ T-cells. Plasma concentrations of adenosine, IL-10, and TGF-β were quantified via an ELISA. An RT-qPCR was used to analyze the gene expression of CD73 and adenosine receptors (A1, A2A, A2B, and A3). T-reg cells were higher in COVID-19 patients compared to healthy controls (7.4 ± 0.79 vs. 2.4 ± 0.28; p < 0.0001). Patients also had a higher frequency of the CD39+ T-reg subset. In addition, patients who suffered from a severe form of the disease had higher CD39+ T-regs compared with moderately infected patients. CD39+CD4+ T cells were increased in patients compared to the control group. An analysis of serum adenosine levels showed a marked decrease in their levels in patients, particularly those suffering from severe illness. However, this was paralleled with a marked decline in the expression levels of CD73. IL-10 and TGF-β levels were higher in COVID-19; in addition, their values were also higher in the severe group. In conclusion, there are distinct immunological alterations in CD39+ lymphocyte subsets and a dysregulation in the adenosine signaling pathway in COVID-19 patients which may contribute to immune dysfunction and disease progression. Understanding these immunological alterations in the different immune cell subsets and adenosine signaling provides valuable insights into the pathogenesis of the disease and may contribute to the development of novel therapeutic approaches targeting specific immune mechanisms.

Dysfunctional purinergic signaling correlates with disease severity in COVID-19 patients

Ectonucleotidases modulate inflammatory responses by balancing extracellular ATP and adenosine (ADO) and might be involved in COVID-19 immunopathogenesis. Here, we explored the contribution of extracellular nucleotide metabolism to COVID-19 severity in mild and severe cases of the disease. We verified that the gene expression of ectonucleotidases is reduced in the whole blood of patients with COVID-19 and is negatively correlated to levels of CRP, an inflammatory marker of disease severity. In line with these findings, COVID-19 patients present higher ATP levels in plasma and reduced levels of ADO when compared to healthy controls. Cell type-specific analysis revealed higher frequencies of CD39+ T cells in severely ill patients, while CD4+ and CD8+ expressing CD73 are reduced in this same group. The frequency of B cells CD39+CD73+ is also decreased during acute COVID-19. Interestingly, B cells from COVID-19 patients showed a reduced capacity to hydrolyze ATP into ADP and ADO. Furthermore, impaired expression of ADO receptors and a compromised activation of its signaling pathway is observed in COVID-19 patients. The presence of ADO in vitro, however, suppressed inflammatory responses triggered in patients’ cells. In summary, our findings support the idea that alterations in the metabolism of extracellular purines contribute to immune dysregulation during COVID-19, possibly favoring disease severity, and suggest that ADO may be a therapeutic approach for the disease.