PULMONARY MACROPHAGES IN BIRDS (BARN OWL, TYTO-TYTO-ALBA), DOMESTIC-FOWL (GALLUS-GALLUS F DOMESTICA), QUAIL (COTURNIX-COTURNIX), AND PIGEONS (COLUMBIA-LIVIA)

Background: Birds have a limited number of resident macrophages in the normal steady-state respiratory tract, The discovery of phagocytes in lavages of lung from birds contrasts with findings that phagocytes ar e seldom seen in investigations in situ, An electron microscopic study was performed in the respiratory units, the parabronchi, and air capi llaries in particular in several adult bird species to localize the se at of respiratory macrophages. Methods: Lung tissue of barn owl, domes tic fowl, quail, and town and homing pigeons was subjected to standard processing for light and electron microscopy after immersion fixation , intratracheal instillation, and intravascular perfusion. Results: Cl usters of macrophages were predominantly housed in the loose connectiv e tissue at the floor of atria at the entrance to the infundibula and gas-exchange tissue proper. Scattered solitary phagocytes were also fo und in connective tissue of air sacs, interatrial septa, and adventiti a of inter- and intraparabronchial arteries and veins and in peribronc hial lymphoid tissue. Phagocytized foreign particulate material mostly consists of hard, dense, crystalline formations surrounded by a limit ing membrane, The transport of small airborne particles occurs via the squamous atrial epithelium to the underlying macrophages, The macroph ages are often accompanied by mast cells. Conclusions: The present res ults demonstrate that avian respiratory macrophages are predominantly located in atrial connective tissue compartments and do not seem to mi grate to the airway surfaces. (C) 1996 Wiley-Liss, Inc.