Phagocytosis of surfactant by alveolar macrophages in vitro

Abstract

Because of their localization and function as phagocytes, alveolar macrophages could take part in the catabolism of surfactant, including surfactants used for treatment. Conditions of the ingestion of the surfactant preparation AWD 56-02 by alveolar macrophages in vitro are described in this paper. The surfactant was labeled with rhodaminyl phosphatidylethanolamine and incubated with alveolar macrophages lavaged from rat lungs. Membrane binding and phagocytosis were evaluated by fluorescence microscopy and quantified fluorimetrically after extraction of the dye. The surfactant was phagocytosed only in the presence of rat serum. The opsonins in the serum are related to complement and Fc receptors as demonstrated by the heat lability of the factor and the inhibition by aggregated gamma-globulins. Furthermore, the phagocytosis depends on calcium and on a factor in the surfactant preparation. Experiments with inhibitors and competition with unlabeled surfactant show that the phagocytosis is a specific and energy-dependent process. Catabolism by alveolar macrophages might be an important step in the metabolism of surfactant, especially when administered in pathological conditions characterized by the presence of serum in the airspaces.

Androgen regulation of lung lipids in the male rat

“…The activity of this enzyme is regulated by various effector molecules (26,27). The lower content of phospholipid in extracellular surfactant may be a consequence of greater uptake by macrophages or increased recycling by neumocytes type II for synthesis of new surfactant (28,29). In our experiment we observed an increased phospholipid concentration in alveolar macrophages of Ca compared to Co.…”

Influence of Blood Constituents on Uptake of a Lipid-Extracted Natural Surfactant by Alveolar Type II Cells

“…No effects were observed for fibronectin, vitronectin, and hemoglobin (Table 3). Bilirubin, usually found at low concentrations in (4) 0.00 f 0.31 (3) 1.85 f 0.45 (4) 0.41 f 0.12 (4) 1.47 f 0.23 (10) 2.07 f 0.29 (8) 2.17 f 0.39 (8) 2.42 * 0.49 (7) 2.36 r 1.16 (3) 0.82 f 0.2 (6) 0.37 f 0.11 (6) 0.27 f 0.18 (6) 3.54 f 1.30 (5) 3.11 f 1.20 (5) 3.58 f 1.80 (5) 1.05 f 0.24 (5) 1.06 f 0.26 (5) 1.47 f 0.43 (5) 0.67 f 0.16 (10) 0.72 f 0.13 (10) 0.43 f 0.19 (10) 0.62 f 0.34 (10) 3 Data are means f SE from n experiments as indicated in parentheses. Cells were isolated from lungs of adult rats, cultured for 18 h. After the preincubation of the cells in a fresh medium for 30 min, a [3H]DPPGlabeled, lipid-extracted, natural surfactant (50 pM) was added, followed by the addition of the serum component or its solvent.…”

“…In vitro uptake of liposomes by macrophages is enhanced by IgG [ 181, fibronectin [ 181, vitronectin [22], and whole serum, respectively, heat-labile components [6]. This effect on surfactant liposomal uptake by alveolar macrophages has been proposed as one of the potential mechanisms for an increased contribution of macrophages in the clearing of alveolar surfactant under pathological conditions [6].…”

“…Whether these or some of the other blood constituents within the alveolar compartment also interfere with the surfactant life cycle and influence the reutilization of lipid components by type I1 cells is not presently known. Increased uptake of surfactant lipid by alveolar macrophages has been observed in the presence of serum [6].…”

Transcriptional responses of Mycobacterium tuberculosis to lung surfactant

“…In principle, Mtb in vivo could utilize surfactant lipids as a nutrient source not only within the alveolar lumen, but also following Mtb phagocytosis by macrophages. It has previously been shown that alveolar macrophages internalize surfactant lipids [32,33,34], which would thus be potentially accessible for metabolic use by intracellular Mtb. Although Mtb bacilli have their own internal lipid stores, the opportunistic use of surfactant lipids for metabolism would reduce the need for de novo synthesis by these organisms.…”