Role of regulatory T cells in recovery after brain ischemi

Resumo

Stroke is the most common neurologic disease and it is an important mortality and disability cause. There is increasing evidence showing that inflammatory response is involved in physiopathology of stroke. One of the cells involved in this response are regulatory T lymphocytes (Treg), a subtype of lymphocytes with an important role in controlling and regulating immune system. Some experimental studies in animal models of brain ischemia proposed a beneficial effect of these cells, however, there are few studies about the role of these lymphocytes in patients with acute ischemic stroke. In this study, we studied the relationship between Treg levels and ischemic stroke outcome. For that purpose, we performed an animal and a clinical study. To study the effect of Treg in an animal model of brain ischemia we performed the next experiments. Firstly, administration of exogenous Treg two hours after ischemia reduced infarct volume and edema at short and long term. This treatment also increases levels of FoxP3 (a specific marker of Treg) within the brain compared to control animals (3.5±0.3 vs 2.3±0.3; p=0.015). Exogenous Treg treatment decreased proinflammatory markers in the brain, such as IL-1β (19.46±1.02 vs 25.92±2.58 pg/ml of total protein; p=0.048) and markers of active inflammation (CD68 and CD11b) compared to controls. There were not changes between treated and control animals regarding neurogenesis and angiogenesis markers. To verify the role of these cells, we administered a treatment with CD28SA (CD28 superagonists), which has previously demonstrated to induce endogenous Treg expansion. Treatment with CD28SA increased Treg levels in peripheral blood and decreased infarct volume in treated animals. We also administered anti-CD25, which has demonstrated to deplete Treg in previous studies. After treatment with anti-CD25, less than 30% of depletion of Treg was achieved in peripheral blood. Infarct volume, edema or FoxP3 and IL-1β levels were not modified in treated animals compared to controls. In the clinical study, we performed a prospective study including 204 patients diagnosed with ischemic stroke within 12 hours from symptom onset and 22 healthy controls. We found that stroke patients showed higher Treg levels at admission (0.0222±0.0177 vs 0.0013±0.0009 %; p<0.0001) and IL-10 seric levels (6.9±1.7 vs 1.8±1.1 pg/mL; p<0.0001) compared to healthy controls. Treg levels increased the first days after ischemic stroke (until day 3) and decreased at day 7. We also found that higher levels of Treg at 48 and 72 hours are related to good functional outcome at 3 months. Higher levels of Treg at 48 and 72 hours were also related to smaller infarct volume and less risk of early neurological deterioration. There is a correlation between Treg levels and IL-10 seric levels after ischemic stroke, showing that IL-10 production could be a mechanism implied in Treg function. Higher levels of Treg were not related with development of infections after stroke. In conclusion, Treg administration in an animal model of brain ischemia decreased infarct volume and edema, without affecting neurogenesis or angiogenesis. In patients, levels of Treg were related to IL-10 seric levels. Higher levels of these cells were related to a better functional outcome, smaller infarct volume, less risk of early neurological deterioration and there was no relationship with infections development. Based on our results, we proposed that expansion of Treg in acute phase of ischemic stroke, constitutes a potential therapeutic option to improve outcome in these patients.