Tuberculosis decreased the expression of HCN1 (1.56 ± 0.31 vs. 0.42 ± 0.02, respectively, independent-sample t test, P < 0.001) and increased the expression of HCN2 (0.07 ± 0.02 vs. 0.35 ± 0.02, respectively, independent-sample t test, P < 0.001), HCN3 (0.07 ± 0.05 vs. 0.17 ± 0.01, respectively, independent-sample t test, P < 0.001) and HCN4 (0.27 ± 0.02 vs. 0.52 ± 0.04, respectively, independent-sample t test, P < 0.001) (Fig. 2b). Here, HCN4 is linked to tuberculosis.