The association of cell type proportions with DNA methylation. The global DNA methylation was decomposed into a set of linearly independent principal component (PC) patterns. Components were used to examine the relationships between global DNA methylation and biological or non-biological covariates (e.g., gender, the batch effect and cell types). (a) The top 5 components (PC1-PC5) with the largest proportion of explained variance from the data. The percentages of explained variance are shown above the bars. (b) The association of the proportion of CD8 + CD28- cells with the first principal component (Spearman’s rank correlation coefficient -0.594 (p = 4.1e-22)) and (c) the association of the proportion of CD4 + CD28- cells with the first principal component (Spearman’s rank correlation coefficient -0.710 (p = 2.5e-14)).