Association of surfactant protein C with isolated alveolar type II cells

Protective Role of Surfactant Protein-D Against Lung Injury and Oxidative Stress Induced by Nitrogen Mustard

Nitrogen mustard (NM) is a vesicant known to cause acute pulmonary injury which progresses to fibrosis. Macrophages contribute to both of these pathologies. Surfactant protein (SP)-D is a pulmonary collectin that suppresses lung macrophage activity. Herein, we analyzed the effects of loss of SP-D on NM-induced macrophage activation and lung toxicity. Wild-type (WT) and SP-D-/- mice were treated intratracheally with PBS or NM (0.08 mg/kg). Bronchoalveolar lavage (BAL) fluid and tissue were collected 14 days later. In WT mice, NM caused an increase in total SP-D levels in BAL; multiple lower molecular weight forms of SP-D were also identified, consistent with lung injury and oxidative stress. Flow cytometric analysis of BAL cells from NM treated WT mice revealed the presence of proinflammatory and anti-inflammatory macrophages. Whereas loss of SP-D had no effect on numbers of these cells, their activation state, as measured by proinflammatory (iNOS, MMP-9), and anti-inflammatory (MR-1, Ym-1) protein expression, was amplified. Loss of SP-D also exacerbated NM-induced oxidative stress and alveolar epithelial injury, as reflected by increases in heme oxygenase-1 expression, and BAL cell and protein content. This was correlated with alterations in pulmonary mechanics. In NM-treated SP-D-/-, but not WT mice, there was evidence of edema, epithelial hypertrophy and hyperplasia, bronchiectasis, and fibrosis, as well as increases in BAL phospholipid content. These data demonstrate that activated lung macrophages play a role in NM-induced lung injury and oxidative stress. Elucidating mechanisms regulating macrophage activity may be important in developing therapeutics to treat mustard-induced lung injury.

Alveolar macrophages, surfactant lipids, and surfactant protein B regulate the induction of immune responses via the airways

The influences of alveolar macrophages (AM) and pulmonary surfactant on the induction of immune responses via the airways were assessed. Mice were depleted of their AM by intratracheal instillation of multilamellar vesicles containing dichloromethylene-diphosphonate followed by intratracheal instillation of a T cell--dependent antigen, trinitrophenyl--keyhole limpet hemocyanin, in vesicles of various compositions. The primary immune response was determined in the spleen of these animals using an ELI-Spot assay. The secondary immune responses in the sera of the mice were assessed using enzyme-linked immunosorbent assays. An immune response was detected in animals depleted of their AM and intratracheally instilled with antigen in small unilamellar vesicles consisting of either phosphatidylcholine cholesterol or surfactant lipids. Incorporation of surfactant protein (SP)-B in the antigen vesicles enhanced the immune response, whereas SP-A or SP-C in the antigen vesicle did not have an effect. Strikingly, intratracheal instillation of SP-B containing antigen vesicles can induce an immunoglobulin M immune response in mice without depletion of AM. These results indicate that SP-B containing vesicles can enhance the induction of immune responses via the airways and further illustrate the important roles of both AM and pulmonary surfactant in the pulmonary immune system.

Pulmonary surfactant: functions and molecular composition

This review briefly notes recent findings important for understanding the surface mechanical functions of pulmonary surfactant. Currently known surfactant-specific proteins and lipids are discussed, with an eye to their possible functions. Competing models of the alveolar subphase life cycle of surfactant are also presented. It is concluded that, in spite of much effort, we still do not understand the basic molecular mechanisms underlying surfactant's rapid adsorption to the air-water interface.

Clearance of SP-C and recombinant SP-C in vivo and in vitro

Surfactant protein (SP) C metabolism was evaluated in vivo by measurements of the clearance of bovine native SP-C (nSP-C) and a recombinant SP-C (rSP-C) in rabbits and mice and in vitro by the uptake into MLE-12 cells. rSP-C is the 34-amino acid human sequence with phenylalanine instead of cysteine in positions 4 and 5 and isoleucine instead of methionine in position 32. Alveolar clearances of iodinated SP-C and rSP-C after tracheal instillation were similar and slower than those for dipalmitoyl phosphatidylcholine (DPC) in the rabbit. nSP-C and rSP-C were cleared from rabbit lungs similarly to DPC, each with a half-life (t1/2) of approximately 11 h. In mice, the clearance of rSP-C from the lungs was slower (t1/2 28 h) than the clearance of DPC (t1/2 12 h). Liposome-associated dinitrophenyl-labeled rSP-C was taken up by MLE-12 cells, and the uptake was inhibited by excess nSP-C. The pattern of inhibition of dinitrophenyl-rSP-C uptake by SP-B, but not by SP-A, was similar to that previously reported for nSP-C. Clearance kinetics of nSP-C were similar to previous measurements of pulmonary clearance of SP-B in rabbits and mice. rSP-C has clearance kinetics and uptake by cells similar to those of nSP-C.