Isolated type II cells from fetal lung as model in studies on the synthesis and secretion of pulmonary surfactant

Interferon production in rat type II pneumocytes and alveolar macrophages

The time course and magnitude of interferon production induced by influenza virus were determined in type II pneumocytes and alveolar macrophages isolated from rats (Sprague-Dawley). Although the peak of interferon production was approximately 20 h in both alveolar cell types, it was more than three- to fourfold higher in type II cells than in macrophages. Dose-response relationships were noted between the virus multiplicity of induction as well as population numbers of either alveolar cell type and interferon yields. The viral-induced cytokines produced by rat type II cells and alveolar macrophages exhibit physiochemical and biological properties characteristic of interferons and, with respect to type II pneumocytes, mark their heretofore unrecognized capability to produce interferon. The best cross-species antiviral protection afforded by these rat interferons to cells of different origin, expressed as percentage of homologous species (100%), was as follows: guinea pig 50, mouse 40%, and both human and monkey 0%. The heterologous antiviral activity by interferons from either rat alveolar macrophages or type II cells on alpha interferon-sensitive guinea pig cells suggests that these cytokines may be more appreciably related to the alpha-like interferon species. The growth of influenza and Sendai viruses was precluded in both rat alveolar macrophages and type II pneumocytes. The findings herein suggest that type II cells may be a major source of alveolar interferon for activating the antiviral state and modulating alveolar cell functions requisite for lung integrity.

A comparison of the specificity of phosphatidylcholine synthesis by human fetal lung maintained in either organ or organotypic culture

Human fetal lung (14-18 weeks gestation) was maintained in either organ or organotypic culture. By 4 days in organ culture or 14 days in organotypic culture, epithelial cells within both culture systems exhibited well-developed apical microvilli and possessed numerous intracellular lamellar bodies characteristic of surfactant phospholipid stores. However, analysis of the pattern of synthesis of individual molecular species of phosphatidylcholine by [14C]choline incorporation and reversed-phase h.p.l.c. showed that this apparent maturation was not paralleled by an increased synthesis of the dipalmitoyl species in either culture system. By contrast, the fractional synthesis of dipalmitoyl phosphatidylcholine, expressed as a percentage of total [14C]choline incorporation, decreased with time in both organ and organotypic culture. Moreover, these fractions were not significantly different from those measured in parallel monolayer cultures of mixed human fetal lung cells that displayed mainly fibroblast morphology. These results suggest that the synthesis pattern of phosphatidylcholine species by lung cells in culture is determined principally by their incubation conditions and not by their state of apparent maturation.

Alveolar pre-type II cells from the fetal rabbit lung: effect of confluence on the production of disaturated phosphatidylcholine

Pre-type II alveolar cells isolated from the fetal rabbit lung on the 24th gestational day have been maintained in vitro for 14 days in a chemically defined medium supplemented with hormone-stripped serum. These cells replicate in culture. Measurement of the incorporation of [14C]choline into cellular disaturated phospholipid indicated that those cells grown in vitro under standard conditions for 8 days (pre-confluent) incorporate the radioactive precursor at a similar rate to cells maintained for 14 days (post-confluent). Both dexamethasone and serum-free medium conditioned by monolayer cultures of fetal rabbit lung fibroblasts stimulated [14C]choline incorporation into disaturated phosphatidylcholine (PC) by the pre- and post-confluent cultures after 24 or 48 h of exposure: the conditioned medium was more effective than the steroid. These treatments had little effect on choline incorporation into disaturated phosphatidylcholine of preconfluent cells during the first 12 h. A marked response occurred by 24 h after which the labelling of disaturated phosphatidylcholine plateaued. In contrast, with post-confluent cells labelling of disaturated PC increased in a more linear fashion and only plateaued after 72 h. Determination of the ratio of incorporation of [14C]choline into disaturated versus unsaturated phospholipid indicated that serum-free medium conditioned by monolayer cultures of fetal lung fibroblasts specifically increased the level of radioactive precursor in the disaturated phospholipid in both the pre- and post-confluent cell monolayers.

Alveolar type II cells isolated from fetal rat lung organotypic cultures synthesize and secrete surfactant-associated phospholipids and respond to fibroblast-pneumonocyte factor

Alveolar type II cells that were isolated from organotypic cultures of fetal rat lung and maintained in primary monolayer culture were analyzed. Morphologically the cells retained many characteristics of type II cells in vivo. Biochemical analysis revealed that the cells contained and synthesized phosphatidylcholine with a high degree of saturation. Furthermore, the cells released saturated phosphatidylcholine and responded to adrenergic stimulation with increased release. The type II cells retained their ability to proliferate and responded to fibroblast-pneumonocyte factor. These data indicate that primary cultures of fetal type II cells will be useful to elucidate mechanisms modulating type II cell proliferation, surfactant synthesis, and surfactant secretion.

Phospholipid-transfer activities in cytosols from lung, isolated alveolar type II cells and alveolar type II cell-derived adenomas

We have examined phospholipid-transfer activities in cytosols from rat and mouse whole lung, isolated rat alveolar type II cells and alveolar type II cell-derived mouse pulmonary adenomas. We report an enrichment in phosphatidylcholine and phosphatidylglycerol (but not phosphatidylinositol) protein-catalysed transfer in the type II cell and adenoma cytosols compared with the whole-lung cytosols. The activities from these cytosols were resolved using column chromatofocusing, which clearly demonstrated the presence of a phosphatidylcholine-specific transfer protein in each of the four tissues. In addition, two proteins (rat) or three proteins (mouse) catalysing both phosphatidylcholine and phosphatidylglycerol transfer were resolved from whole lung, whereas in both the rat isolated alveolar type II cells and the mouse type II cell-derived adenomas one of these less specific proteins is not present.