CD28 and chronic obstructive pulmonary disease: We hypothesized that (a) CD28nullCD8+ T and NKT-like cells migrate to the lungs of COPD patients, and that the migration is facilitated by BLTR1 expression, and (b) once in the airways, the loss of CD28+ expression with subsequent loss of BLTR1 allows for random migration of these cytotoxic, pro-inflammatory cells from the lung into the peripheral blood resulting in systemic inflammatory disease.