Stimulatory and Inhibitory Activities of Lung-Conditioned Medium on the Growth of Normal and Neoplastic Cells in Vitro2

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Abstract
Lung-conditioned medium (LCM) was obtained by incubation of BALB/c mouse lung tissue fragments in serum-free Eagle medium for 48 hours and subsequent separation by dialysis or chromatography on a Sephadex G-75 column. LCM fractions were tested for their ability to modulate proliferation of normal human endothelial cells and neoplastic cells (N2a, MCF, HEp-2) in vitro as assessed by plating efficiency and tritiated thymidine incorporation assays. It was found that LCM contained two kinds of factors, either stimulating (molecular weight: 50,000–70,000) or inhibiting (molecular weight: 12,000–20,000 and 3,000–5,000) cell proliferation.