The expression levels of Notch ligand Dll4 in the peripheral blood of the HFMD group correlated negatively with the numbers of peripheral CD3+ (R-square = −0.299, p = 0.004) and CD3+CD8+ (R-square = −0.234, p = 0.025) lymphocytes, but correlated positively with the number of peripheral CD3−CD19+ lymphocyte (R-square = 0.364, p = 0.000) (Figure 3). Here, DLL4 is linked to hand, foot and mouth disease.