To investigate this hypothesis, we compared the immunophenotypes of pediatric and adult PAD patients classified as having severe PAD and found that pediatric patients had higher absolute counts of CD3+ T-cells (1,688.9 vs. 848.3 cells/uL; p=0.05), CD4+ T-cells (918.2 vs. 402.8 cells/uL; p=0.04), CD19+ B-cells (432.6 vs. 74.3 cells/uL; p=0.0004), and CD19+CD27+IgM-IgD- class-switched memory B-cells (16.3 vs. 2.0 cells/uL; p=0.002) (Supplemental Table 1). This evidence concerns the gene CD19 and peripheral arterial disease.