Some findings suggest immunological senescence in COPD patients, with an increased proportion of T lymphocytes lacking CD28 co-stimulatory receptor expression (CD4+CD28- and CD8+CD28- cells); these cells release higher amounts of perforins and granzymes and are more resistant to apoptosis (6) and potentially steroid-unresponsive (10). Here, CD28 is linked to chronic obstructive pulmonary disease.