Tissue factor activity. A marker of alveolar macrophage maturation in rabbits. Effects of granulomatous pneumonitis.

Experiments were carried out to examine relationships between alveolar macrophage maturity and amounts of tissue factor (Clotting Factor III) in these cells under physiologic conditions and during immunologically induced pneumonitis. Using discontinuous density gradient centrifugation, alveolar macrophages from healthy rabbits were rapidly isolated into five subpopulations at different stages of maturation, as demonstrated by morphologic and morphometric evaluation. Very large amounts of tissue factor activity were found in fully mature cells that were purified in the lowest density subpopulation and assayed without preliminary in vitro stimulation or culture. In the remaining four subpopulations of increasing density, amounts of tissue factor were found to progressively diminish in direct correlation with declines of cell maturity. These differences at mean levels were as great as 35-fold. In addition, blood monocytes had less than 1/219 and less than 1/6 of the activity of the fully mature and the least mature subpopulations, respectively. After 16 h culture of the five isolated subpopulations in the absence of lymphokines or of significant numbers of lymphocytes, tissue factor activity increased in inverse correlation with the preincubation stage of cell maturity (2,387 and 109% in the least mature and most mature subpopulations, respectively). These increases required protein synthesis and were accompanied by morphologic and morphometric changes which indicated cellular maturation during the period of tissue factor activity generation in vitro, thus further demonstrating relationships between macrophage maturity and tissue factor content. In additional experiments, direct correlations between cell maturity and tissue factor activity content were also found in activated alveolar macrophage populations from rabbits with Bacillus Calmette Guering (BCG)-induced granulomatous pneumonitis. However, as compared with controls, the BCG populations had increased total amounts of tissue factor activity due to the presence of large numbers of mature alveolar macrophage forms that had high levels of the procoagulant. Thus, tissue factor activity in alveolar macrophages is a marker of cellular maturation in vivo and in vitro. Increased amounts of this initiator of the extrinsic clotting pathway, as found in alveolar macrophage populations from animals with granulomatous pneumonitis induced by BCG hypersensitivity, suggest that alveolar macrophage tissue factor may contribute to the pathology of immune lung diseases.