PLATELET-DERIVED GROWTH FACTOR-AA AND FACTOR-AB DIMERS ARE PRESENT INNORMAL HUMAN EPITHELIAL LINING FLUID

Normal lung architecture is related to the presence of mesenchymal cel ls (fibroblasts and smooth muscle cells), and to the production by the se cells of extracellular matrix. The turnover of mesenchymal cells is under a fine regulation due, at least in part, to the local presence of different mediators acting on their cell cycle. Since normal human alveolar macrophages obtained by bronchoalveolar lavage (BAL) spontane ously release platelet-derived growth factor (PDGF), a cytokine with c hemotactic and growth activity on mesenchymal cells, we evaluated norm al human epithelial lining fluid (ELF) for the presence of PDGF. Activ e only as a dimer, PDGF is a glycoprotein composed of two chains (A an d B) and, thus, can be present in three forms: AA, AB, and BB dimers. Interestingly, normal ELF contains PDGF AA dimers, and to a lesser ext ent AB dimers, while no significant level of BB dimers is detected. Fu rthermore, ELF PDGF is biologically active and responsible for a signi ficant part of the chemotactic activity and the ''competence'' growth activity for mesenchymal cells present in normal ELF. These findings s uggest that ELF PDGF has a role in normal lung structure maintenance a nd tissue repair.