Regulatory T cells: a brake on ischemic injury or an active promoter of tissue healing?

Ulinastatin ameliorates acute kidney injury induced by crush syndrome inflammation by modulating Th17/Treg cells

BACKGROUND

Acute kidney injury (AKI) is the main complication of crush syndrome (CS), and it is also a cause of lethality in CS. However, effective treatments for AKI are still lacking. Ulinastatin (UTI) is a broad-spectrum serine protease inhibitor extracted from human urine that reportedly modulates innate immunity and pro-inflammatory responses in sepsis. Here, we explored the effect and the potential mechanism of ulinastatin on crush syndrome-induced acute kidney injury (CSAKI).

METHODS

A CSAKI rat model was established by using a digital crush injury device platform. Forty-six male Wistar rats were randomly divided into five groups: the normal control (n = 6), CSAKI model (n = 10), CSAKI plus UTI1 (50,000 U/kg) (n = 10), CSAKI plus UTI2 (100,000 U/kg) (n = 10) and CSAKI plus UTI3 (200,000 U/kg) (n = 10) groups. Hematoxylin-eosin (HE) staining was used to investigate the reliability of the CSAKI model. The percentage of Th17/Treg lymphocytes in peripheral blood was measured by flow cytometry, and the expression of transcription factors associated with Th17/Treg cells was evaluated by quantitative real-time polymerase chain reaction (PCR). In addition, specific cytokines released by Th17/Treg cells in serum and kidney tissues were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Treatment with ulinastatin could significantly decrease serum BUN, CK, Scr, Mb and K⁺ levels compared with CSAKI group. HE staining results showed that ulinastatin could inhibit inflammatory cells infiltration, decrease sarcomere rupture in muscle tissues induced by extrusion, and alleviate the glomerular congestion and edema, as well as decrease myoglobin cast in kidney tissues. The proportion of CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells and Foxp3 expression levels were decreased in the CSAKI animals, while IL-17 expression levels were significantly increased, compared with those of the normal control group. Treatment with ulinastatin upregulated the proportion of Treg cells in CD4⁺ T cells and downregulated the expression of IL-17 compared with those of the CSAKI group.

CONCLUSION

The findings of our study indicate that UTI attenuates CS-induced AKI and alleviate the inflammatory response during the early stage. The mechanism of UTI may be due to regulating the balance between Th17/Treg cells. Our study provides a new mechanism for the beneficial effect of ulinastatin on CSAKI.

The paradox role of regulatory T cells in ischemic stroke

The underlying mechanism of ischemic stroke is not completely known. Regulatory T cells (Tregs), a subset of T cells, play a pivotal role in the pathophysiological process of ischemic stroke. However, there is also controversy over the role of Tregs in stroke. Hence, the function of Tregs in ischemic stroke has triggered a heated discussion recently. In this paper, we reviewed the current lines of evidence to describe the full view of Tregs in stroke. We would like to introduce the basic concepts of Tregs and then discuss their paradox function in ischemic stroke. On one side, Tregs could protect brain against ischemic injury via modulating the inflammation process. On the other side, they exaggerated the insult by causing microvascular dysfunction. They also interfered with the neurological function recovery. In addition, the reasons for this paradox role would be discussed in the review and the prospective of the clinical application of Tregs was also included. In conclusion, Tregs contributed to the outcome of ischemic stroke, while more lines of evidence are needed to understand how Tregs regulate the immune system and influence the outcome of stroke.

Adoptive regulatory T-cell therapy preserves systemic immune homeostasis after cerebral ischemia

BACKGROUND AND PURPOSE

Cerebral ischemia has been shown to result in peripheral inflammatory responses followed by long-lasting immunosuppression. Our recent study demonstrated that intravenous delivery of regulatory T cells (Tregs) markedly protected against transient cerebral ischemia by suppressing neutrophil-derived matrix metallopeptidase 9 production in the periphery. However, the effect of Tregs on systemic inflammatory responses and immune status has not been fully characterized.

METHODS

Cerebral ischemia was induced by middle cerebral artery occlusion for 60 minutes in mice or 120 minutes in rats. Tregs were isolated from donor animals by CD4 and CD25 double selection and transferred intravenously to ischemic recipients at 2 hours after middle cerebral artery occlusion. Animals were euthanized on different days after reperfusion. The effects of Tregs on systemic inflammation and immune status were evaluated using flow cytometry, ELISAs, and immunohistochemistry.

RESULTS

Systemic administration of purified Tregs raises functional Tregs in the blood and peripheral organs, including spleen and lymph nodes. These exogenous Tregs remain in the blood and peripheral organs for ≥12 days. Functionally, Treg adoptive transfer markedly inhibits middle cerebral artery occlusion-induced elevation of inflammatory cytokines (interleukin-6 and tumor necrosis factor α) in the blood. Furthermore, Treg treatment corrects long-term lymphopenia and improves cellular immune functions after ischemic brain injury. As a result, Treg-treated animals exhibit decreased bacterial loads in the blood during recovery from cerebral ischemic attack.

CONCLUSIONS

Treg treatment did not exacerbate poststroke immunosuppression. On the contrary, Treg-treated animals displayed improved immune status after focal cerebral ischemia.