Background: Cell adhesion molecules are believed to be essential for blood cell recruitment to the lung and for the movement of alveolar macrophages (AM) within the lung. Objective: To investigate the expression pattern of L-selectin and β₂ integrins on blood leukocytes and AM, including AM of various maturity. Methods: Flow cytometry was used to study the expression of L-selectin (CD62L) and of the β₂ integrins CD11a, CD11b, and CD11c on AM (including density-defined subpopulations), monocytes (Mo), polymorphonuclear neutrophils (PMN) and lymphocytes (Ly) sampled from healthy individuals, during incubation with and without lipopolysaccharide (LPS). Results: A significantly different modulation pattern of β₂ integrins and L-selectin was demonstrated on Mo and AM, cells of the same differentiation lineage. In contrast to AM, Mo had a marked ability to respond to LPS stimulation by increased expression of CD11a, CD11b and CD11c and decreased expression of L- selectin. These molecules were expressed to a similar degree on AM, whereas the basal levels of CD11b and L-selectin were considerably higher on Mo than on AM. A significantly different expression of CD11a as well as differences in the regulation of L-selectin during incubation were also demonstrated between density-defined subpopulations of AM. CD11a could not be upregulated on PMN, otherwise the modulation patterns of CD11b, CD11c and L-selectin were similar to that on Mo. The expression of CD11a on Ly was 3- to 6-fold higher than on Mo, PMN and AM. The level of CD11b decreased significantly upon incubation (uninfluenced by LPS stimulation), and CD11c was hardly expressed on Ly. The level of L-selectin on Ly was higher than on Mo, AM and PMN and was not decreased during incubation. Conclusion: Developmental origin, degree of cell differentiation (maturity) as well as different environmental conditions all heavily influence the expression and modulation pattern of β₂ integrins and L-selectin on leukocytes and Mo-derived AM.

We have studied the expression of the lipopolysaccharide (LPS) receptor CD14 on monocytes (Mo) and alveolar macrophages (AM), including density- and size-defined subpopulations. Bronchoalveolar lavage (BAL) was performed on eleven healthy non-smokers and blood sampled from 5 of them, and the levels of cell CD14 expression was investigated using flow cytometry. The influence of LPS stimulation on the CD14 expression of AM was studied at various intervals during prolonged incubation. Further, the relationship between CD14 expression and LPS binding to Mo and subpopulations of AM was studied by measuring fluorescein isothiocyanate (FITC)-LPS binding (flow cytometry) and binding of radioiodinated LPS (125I-LPS). The CD14 expression was 13-fold higher (P < 0.02) on Mo than on unfractionated and high density AM. The CD14 level on the latter was higher than on low density AM, and also higher (P < 0.05) on small AM compared to large (flow cytometrically defined) AM. LPS stimulation had a downregulating effect on AM CD14 level, but after several hours of continuing decreased expression, an increased (P < 0.05) CD14 expression was demonstrated, indicating de novo synthesis. The binding of LPS to subpopulations of AM and isolated Mo was not significantly different, but the binding of FITC-LPS to Mo in whole blood was higher than to AM (P < 0.02). The presented results indicate that AM of different size and maturity have different and variable (activation dependent) CD14 levels. The LPS binding capacity was, however, not proportional to the CD14 expression, indicating that LPS binding mechanisms unrelated to CD14 levels were also operable.

The development of adult respiratory distress syndrome (ARDS), infant respiratory distress syndrome (IRDS) and septicaemia is known to be associated with pulmonary intravascular, interstitial and intra-alveolar deposition of fibrin [1]. The formation of fibrin during injury and inflammatory reactions, followed by its clearance during the repair process, is the result of a dynamic interplay between coagulant and fibrinolytic factors which amongst other cells are synthesized by peripheral blood monocytes, lung alveolar macrophages (AM) and lung interstitial macrophages [2][3][4]. Tissue factor (TF), which is produced by mononuclear phagocytes, is a receptor for coagulation factor VII [5] and plays an important role in the initiation of intravascular and extravascular coagulation leading to fibrin generation [2,3]. Owing to their expression of strong procoagulant (TF) activity, monocytes and AM represent foci for the deposition of fibrinogen and/or fibrin in vivo [6] and in vitro [7,8]. Binding of fibrinogen to specific receptors on blood monocytes has also been postulated to play a specific role in the differentiation of monocytes into macrophages [9]. Both monocytes and AM express β 2 -integrins (CD11b/CD18 and CD11c/CD18) on the cell surface which, in addition to mediating intercellular adhesion [10], have been shown to bind fibrinogen and factor X [11][12][13]. Coordinated membrane expression of procoagulant activity (TF) and receptors for coagulation factors (CD11b/CD18 and CD11c/CD18) would facilitate fibrin deposition when plasma factors and cofactors are supplemented. It is not known, however, whether these molecules are presented in a concerted fashion on the cell surface or whether they are independently regulated. Blood monocytes and AM are both members of the same cell differentiation (monocyte) lineage, but they are normally exposed to a different local milieu. It was, therefore, of interest to compare their response to the biologically highly active stimulant lipopolysaccharide (LPS), which in vivo is a potential candidate for cell stimulation during systemic pathological conditions such as septicaemia, but also locally when micro-organisms are introduced via the respiratory tract. LPS is a bacterial product of the outer membrane of Gram-negative bacteria which exerts its effects both directly, but also indirectly via the release of proinflammatory cytokines such as tumour necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6. The intention of this study was, therefore, to compare the baseline expression of TF and β 2 -integrins on blood monocytes and AM and to examine the changed expression induced by LPS challenge. Materials and methods Bronchoalveolar lavageBronchoalveolar lavage (BAL) was performed in healthy, nonsmoking volunteers with normal lung function Expression of leukocyte integrins and tissue factor in mononuclear phagocytes. B. Nakstad, T. Haugen, O.H. Skjønsberg, T. Lyberg. ©ERS Journals Ltd 1998.ABSTRACT: Coagulation is intimately involved in the pathology of inflammation. The leukocyt...

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We have studied the expression of tissue factor (TF) and fibrinopeptide A (FPA) generation as well as the release capacity of TNF-alpha, IL-1beta, and IL-6 in density-defined subpopulations of alveolar macrophages (AM) and monocytes (Mo). TF was equally expressed on all AM subpopulations and Mo, while the FPA-forming capacity was at the same level in low density AM as in Mo and was significantly (P < 0.05) higher in low density AM than in high density AM. The lipopolysaccharide (LPS)-induced release of TNF-alpha was higher (P < 0.05) in high density AM than in low density AM and in Mo. IL-1beta release was undetectable in unstimulated AM and in LPS-stimulated low density AM, while the LPS-induced IL-1beta release in high density AM was low compared to the levels demonstrated in Mo. LPS-stimulated IL-6 release was not distinctively different in the AM subpopulations and Mo. The presented study showed that FPA generation and LPS-stimulated TNF-alpha release were dependent on the density (i.e., maturity) of AM. This implies that a skewed distribution of AM subpopulations induced by disease processes may profoundly influence the inflammatory reactions, including extravascular activation of coagulation.