Ischemic transient neurological events identified by immune response to cerebral ischemia

Abstract

Background and purpose: Deciphering whether a transient neurological event (TNE) is of ischemic or nonischemic etiology can be challenging. Ischemia of cerebral tissue elicits an immune response in stroke and transient ischemic attack (TIA). This response, as detected by RNA expressed in immune cells, could potentially distinguish ischemic from nonischemic TNE.

Methods: Analysis of 208 TIAs, ischemic strokes, controls, and TNE was performed. RNA from blood was processed on microarrays. TIAs (n=26) and ischemic strokes (n=94) were compared with controls (n=44) to identify differentially expressed genes (false discovery rate <0.05, fold change ≥1.2). Genes common to TIA and stroke were used predict ischemia in TIA diffusion-weighted imaging-positive/minor stroke (n=17), nonischemic TNE (n=13), and TNE of unclear etiology (n=14).

Results: Seventy-four genes expressed in TIA were common to those in ischemic stroke. Functional pathways common to TIA and stroke related to activation of innate and adaptive immune systems, involving granulocytes and B cells. A prediction model using 26 of the 74 ischemia genes distinguished TIA and stroke subjects from control subjects with 89% sensitivity and specificity. In the validation cohort, 17 of 17 TIA diffusion-weighted imaging-positive/minor strokes were predicted to be ischemic, and 10 of 13 nonischemic TNE were predicted to be nonischemic. In TNE of unclear etiology, 71% were predicted to be ischemic. These subjects had higher ABCD(2) scores.

Conclusions: A common molecular response to ischemia in TIA and stroke was identified, relating to activation of innate and adaptive immune systems. TNE of ischemic etiology was identified based on gene profiles that may be of clinical use once validated.

Figures

Figure 1

Flow diagram of study analyses. A. To derive common ischemia genes, TIA and ischemic stroke subjects were compared to controls. Of the 160 probesets differentially expressed in TIA, 74 (46%) were identical to those in ischemic stroke (FDR<0.05, fold change ≥1.2∣). A subset of 26 probesets were found to optimally distinguish TIA and ischemic stroke from controls using LDA. B. A prediction model using these 26 probesets was developed and evaluated by cross-validation on the original validation cohort, and on a validation cohort of TNE of known ischemic and nonischemic etiology. C. The 26 probesets were subsequently used to predict ischemia in TNE of unclear etiology.

Figure 2

Proportional representation of the immune cells that contributed to RNA expression in blood in TIA and ischemic stroke patients. Previous studies have identified genes unique to each cell type in blood . These profiles were used to identify cells contributing to the differentially expressed genes in TIA and stroke. The genes differentially expressed in TIA were associated mostly with granulocytes and B-cells. The genes differentially expressed in ischemic stroke were associated mostly with granulocytes, monocytes, natural killer cells and B-cells, with some contribution from megakaryocytes and CD4 T-cells.

Figure3

Probability plots of the predicted diagnosis of cerebral ischemia in TIA and ischemic stroke versus controls. The predicted probabilities are from cross-validation of the LDA 26 common ischemic gene model on the derivation cohort. The predicted probability of ischemia versus nonischemia in shown for (3A) the 26 patients clinically diagnosed as TIA; (3B) the 94 with ischemic strokes; (3C) the 44 vascular risk factor controls. The probability of a subject being ischemia is shown in red, and the probability of a subject being nonischemia is shown in blue. Cerebral ischemia was correctly predicted in 89% of subjects, and nonischemia was correctly predicted in 89% of controls. The probability of predicted diagnosis for the majority of subjects was >90%.