LYMPHOCYTE DYNAMICS - CAUTION IN INTERPRETING BAL NUMBERS

In various allergic and inflammatory lung diseases the number and subs et composition of lymphocytes in the bronchoalveolar lavage (BAL) flui d are taken as indicators of the state of the disease. The number of l ymphocytes in the BAL fluid depends on three main parameters: (1) entr y into the bronchoalveolar space from the different compartments of th e lung, (2) persistence in the bronchoalveolar space which is modified by the rate of local proliferation and apoptosis, and (3) exit into t he draining bronchial lymph node via the lymphatic system. In healthy individuals lymphocytes in the BAL fluid seem to be a stable pool: eac h day there is hardly any entry, local cell. division or cell death an d few lymphocytes emigrate from this compartment. In contrast, during inflammatory, toxic and allergic reactions all parameters can increase rapidly with more lymphocytes entering, proliferating and/or undergoi ng apoptosis locally. Very little is known about factors such as cytok ines and chemokines which may regulate these parameters. When interpre ting data on lymphocyte numbers in patients, lymphocyte dynamics in th e bronchoalveolar space have to be considered, and in the future it ma y be possible to manipulate these lymphocyte fluxes for therapeutic pu rposes.