Lymphocytes migrate from the blood into the bronchoalveolar lavage and lung parenchyma in the asthma model of the brown Norway rat

Lymphocyte migration from the blood into the lung has been suggested as bei ng responsible for the increase of lymphocytes, in particular CD4 T cells, in the bronchoalveolar lavage (BAL) and bronchial mucosa in human asthma, b ut, so far there has been no direct proof. We studied lymphocyte immigratio n and lymphocyte subpopulations in three lung compartments in ovalbumin (OV A)-sensitized and -challenged brown Norway (BN) rats. Increased numbers of CD4 and interleukin 2 (IL-2) receptor-positive T cells were found in the BA L and lung parenchyma in treated animals, but also increased numbers of CD8 T cells, B cells, and natural killer (NK) cells. For direct: proof of lymp hocyte migration from the blood into the lung, leukocytes were labeled with a fluorescent dye, 5- (and 6-) carboxyfluorescein-diacetate-succinimidyl-e ster (CFSE), and injected intravenously immediately prior to OVA aerosol ch allenge. One day after challenge the number of CFSE+, i.e, newly immigrated lymphocytes, was determined by flow cytometry gated on the lymphocyte clus ter, A 15 times (1.5 times) higher number of CFSE+ lymphocytes was found in the BAL (the lung parenchyma) of treated animals in comparison with contro l rats. In the BAL 51.8% of CFSE+ cells were CD4-positive (parenchyma 72.7% ) and 29.4% IL-2 receptor-positive (parenchyma 34.2%). There was no differe nce whether the leukocytes for labeling and injection were obtained from un treated or from OVA-sensitized donor animals. Our data show that lymphocyte immigration is at least in part responsible for the increase in lymphocyte numbers in the BAL and lung parenchyma in this animal asthma model.