CD4 and chronic obstructive pulmonary disease: This change occurred both as a percent of all CD45+ cells (CD4+ T cells: stable, 17.4 ± 1.7 % of CD45+ leukocytes vs. during AE-COPD, 10.0 ± 4.2 %; mean ± SEM; p = 0.002) (CD8+ T cells: stable, 10.4 ± 2.2 % vs. AE-COPD, 5.9 ± 1.0 %; p = 0.02) and in absolute numbers.