CD4 and chronic obstructive pulmonary disease: Studies indicate elevated levels of CD8+ T lymphocytes in the blood and airway tissues of COPD patients, alongside increased numbers of activated CD4+ and CD8+ cells expressing nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), signal transducer and activator of transcription 4 (STAT-4), interferon-γ (IFN-γ), and perforin [21, 22].