Variation of Bronchoalveolar Lymphocyte Phenotypes with Age in the Physiologically Normal Human Lung

Background: Changes in T lymphocyte subsets have been observed in various forms of pulmonary disease. However, bronchoalveolar lymphocyte subsets have not been well characterised for healthy individuals differing in age. A study was undertaken to investigate the bronchoalveolar lavage (BAL) and peripheral blood lymphocyte subsets in clinically normal volunteers of two different age groups (19-36 and 64-83 years).

Methods: Bronchoalveolar lavage was performed on all individuals in both age groups and peripheral venous blood was drawn just prior to BAL. Bronchoalveolar cell profiles were characterised by morphological criteria, and cell surface antigen expression of lymphocytes was determined by flow cytometry.

Results: A significant increase in total BAL lymphocytes was observed for the oldest group compared with the youngest age group. Mean lymphocyte subset (CD4+/CD8+) ratios were significantly increased in BAL fluid from the older group compared with the younger group (mean (SE) 7.6 (1.5) vs 1.9 (0.2); p<0.0001). The increase in the BAL CD4+/CD8+ T cell ratio was mostly due to an increase in relative numbers of CD4+ lymphocytes, and the BAL CD4/CD8 ratio was disproportionately increased compared with peripheral blood in the older group. Increased expression of HLA-DR and CD69 on CD4+ T lymphocytes was observed in the oldest age group. Relative numbers of natural killer (NK) cells did not vary with age, and gammadelta T cells and CD5+ B cells were present in very low numbers in both age groups.

Conclusions: CD4+ T cells accumulate in air spaces of the lower respiratory tract with age in healthy adults and express increased amounts of HLA-DR and CD69 on their surfaces, suggesting a relative degree of CD4+ T lymphocyte activation for healthy older individuals who have normal lung function.