Density and substrata are important in lung type II cell transdierentiation in vitro L.J. Reynolds a , M. McElroy b , R.J. Richards a, * a Cardi School of Biosciences, Cardi University, P.O. Box 911, Cardi CF1 3US, UK b Rayne Laboratories, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, UK Received 6 January 1999; accepted 17 June 1999 Abstract Morphological techniques and metabolic cell marker assays were used to study the transdierentiation of pulmonary type II epithelial cells to type I-like cells in vitro. In the lung this process is important during remodelling and alveolar repair. Type II cell phenotype was best maintained over eight days when densely packed cells were plated out on a commercially available extracellular matrix. Such cells retained type II cell characteristics (lamellar bodies, high activities of gamma glutamyl transpeptidase and alkaline phosphatase) but expressed low levels of rT1 40 a surface protein marker of type I cells. In contrast, low density cultures, irrespective of substratum, exhibited rapid cell spreading, loss of lamellar bodies, loss of type II cell enzyme markers and expressed high levels of rT1 40 . Conditions have been described whereby the same isolate of type II cells can be used to produce dierential epithelial phenotypes and use can be made of this for further characterisation or to investigate the eect of toxins on dierent lung cell types in vitro. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Alveolar type II cell; Type I-like cell; Transdierentiation; Matrices 1. Introduction The type II cell comprises about 14% of the total alveolar population, is typically cuboidal in shape and situated in the corner of the alveolus. Type II cells synthesise and secrete pulmonary surfactant, a lipoprotein complex responsible for the unusually low surface tension at the air± liquid interface of the lung. They also contain the biotransformation enzymes which include the P450 monooxygenases enzymes Ð a superfamily of genes whose proteins are involved in degrad- ing toxins. In addition, considerable interest has focused on the ability of a type II cell to repair the alveolar epithelium following cellular damage [1] and whether part of this process may be fol- lowed with cultures of type II cells as they change to type I-like cells in vitro [2]. Type II cells cultured on tissue culture plastic rapidly lose The International Journal of Biochemistry & Cell Biology 31 (1999) 951±960 1357-2725/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S1357-2725(99)00052-7 www.elsevier.com/locate/ijbcb * Corresponding author. Tel.: +44-1222-876-659; fax: +44- 1222-874-125. E-mail address: richardsrj@cardi.ac.uk (R.J. Richards)