Transcriptional patterns of airway epithelial microRNAs during acute cellular rejection (ACR). A. Principal component analysis of the entire microRNA expression profiles (742 microRNAs) across 21 lung transplant recipients (n = 10 with ACR, n = 11 without rejection) yielded reasonable separation between the two patient groups. This implied the presence of significant global expression differences between the two groups. Each axis explains a proportion of the variability in microRNA expression, thereby determining the spatial location of the subjects. Note that for PCA we used information across all 742 microRNAs, including many that were not differentially expressed between the two groups, thereby reducing power for segregating patients with and without ACR. B. Heatmap depiction of 117 differentially expressed microRNAs in ACR after adjustment for multiple testing using FDR < 0.05. Note that almost all microRNAs were downregulated in the airway epithelium of subjects with ACR, implying activation of their corresponding gene targets.