Increased expression of activation markers and adhesion molecules on lung T-cells compared with blood in the normal rat.

Lymphocytes play an important role in many lung diseases and are routinely accessible by bronchoalveolar lavage (BAL). Lymphocytes from the BAL (BAL pool) have a different subset composition to those from peripheral blood, consisting mainly of activated T-cells. The aim of this study was to examine whether preferential migration of activated T-cells to the bronchoalveolar space or factors of the specific microenvironment mediate this phenomenon. The expression of adhesion molecules and cellular activation markers (intercellular adhesion molecule-1, leukocyte function-associated antigen-1, CD2, CD44, interleukin-2 receptor and L-selectin) was studied on T- and B-cells not only in the BAL and peripheral blood (blood pool), but also in the compartments in between, such as the lung vascular perfusate (marginal pool) and the lung interstitium (interstitial pool), with the experiments being performed simultaneously in the same animals. Low levels of adhesion molecule expression were observed on T-cells in the blood and marginal pool, medium levels in the lung interstitium and the highest levels in the BAL. "Memory" (CD45R(low)) and "naive" (CD45R(high)) T-cells in the lung compartments showed a higher expression of adhesion molecules compared with blood. However, the predominating CD45R(low) T-cells showed a significantly higher expression than the CD45R(high) cells, indicating that CD4+ CD45R(high) T-cells had changed their phenotype to CD45R(low). In conclusion, a high level of expression of leukocyte function associated antigen-1 and intracellular adhesion molecule-1 on the bronchoalveolar lavage and interstitial T-cells is more likely to be the result of local, lung-specific induction than a prerequisite for migration into the bronchoalveolar space.