The expression of several activation markers, such as CD25 [21], CD28 [20], CD29 [20], CD45RO [20], and HLA-DR [19,21], by systemic CD4+ and CD8+ T lymphocytes was also found to be similar between COPD smokers, normal smokers, and normal non-smokers. Here, ITGB1 is linked to chronic obstructive pulmonary disease.