Abstract W P87: Characteristics of T-cells Infiltrating Ruptured Intracranial Aneurysm

Introduction: Recently the role of adaptive immunity has been implied by microarray studies. But the results are contradictory. T-cell infiltration is a frequent histological finding in ruptured IA, T-cell phenotype, characteristic and true quantitation remains unknown. We preformed a prospective study to determine the subpopulation and expression of activation markers of T-cells infiltrating ruptured IA in relation to peripheral blood. Hypothesis: IA have different subsets and activation levels of T-cells than peripheral blood. Methods: We collected the tissue of ruptured IA of 8 patients operated on within 24 hours after subarachnoid hemorrhage symptoms onset. IA tissue was digested, stained with fluorescently labeled monoclonal antibodies and submitted to flow cytometry. In addition we collected and analyzed venous blood from 6 age, sex and risk factor-matched controls. Results: CD4+ cells are less prevalent in IA tissue than in peripheral blood (42.14±17.28 vs. 65.88±5.32%; p=0.011), while there was no difference in CD8+ T-cells infiltrating IA (30.28±9.07 vs. 27.78±5.45%; p=0.585), and double negative (CD4-CD8-CD3+) T-cells were more prevalent in wall of IA than in circulation, (15.68±11.94 vs. 2.81±1.32%; p=0.026). Importantly, CD4+ infiltrating IA wall showed higher expression of HLA-DR (25.9±6.42 vs. 9.19± 3.58%; p<0.001) higher expression of CD 69 (26.8±19.66 vs. 2.73±0.93%; p=0.014). Similarly, there significantly more CD8+ cells showed HLA-DR+ in the IA than in blood. (45.96±15.57 vs. 22.47±11.46%; p=0.018) and CD69 (30.32±22.73 vs. 5.03±1.55%; p=0.022). Double negative cells in IA also had higher expression of HLA-DR (46.56±21.40 vs. 22.58±5.1%; p=0.025), CD69 (31.05±16.79 vs. 7.83±2.05%; p=0.016). Conclusion: The tissue of ruptured IA is highly infiltrated by T-cells which show high expression of activation markers such as CD69 or HLA-DR. The importance of these cells to immunopathogenesis of intracranial aneurysm rupture should be further characterized.