Interferon: Effect on the Saturation Density to Which Mouse Cells Will Grow in Vitro

Interferon is a protein secreted by animal cells, when stimulated by certain agents, which has the ability to induce in homologous cells a resistance to replication of a wide variety of viruses (1, 2). Moreover, preparations of mouse interferon, both crude and partially purified, have been shown to inhibit the growth of mouse L cells (3) and mouse lymphoid leukemia cells (4) in suspension culture. Recently, crude preparations of mouse interferon have been reported to inhibit the growth in mono-layer culture of L, mouse embryo, and mouse kidney cells (5). The term "density-dependent inhibition" of cell growth has been proposed to describe the termination of animal cell growth in monolayer culture when a certain density of cells per square centimeter of surface is reached (6). The final density to which a given type of cells will grow is called its "saturation density". Some cells are more sensitive to density restriction than others, e.g., viral-transformed mouse 3T3 cells are much less restricted than the original 3T3 cells (7). In this communication the effect of partially purified preparations of mouse interferon on the saturation densities of various mouse cells is reported. Cells Mouse L cells were maintained in suspension culture in Eagle's suspension culture medium (Joklik modified) supplemented with 10% fetal calf serum. The cell concentration was maintained at 10-80 X l04 cells/ml and an equal volume of fresh medium was added every 24 h. Monolayer cultures of L cells were prepared by adding an equal volume of Eagle's minimum essential medium, supplemented with 10% fetal calf serum, to an equal volume (or less) of suspension culture and plating in a 50 mm plastic Petri dish. Mouse 3T3 cells and SV-40-transformed 3T3 (SV-3T3) were a gift to Dr. T. Sugiyama from Dr. H. Green. Polyoma-transformed 3T3 (Py-3T3) was a gift to Dr. T. Sugiyama from Dr. M. Burger. Cultures of 3T3, SV-3T3, and Py-3T3 cultures were maintained in Dulbecco's modified Eagle's medium supplemented with 10% calf serum. M[ouse embryo secondary cultures were prepared from 5-day old primary cultures and maintained in Eagle's minimum essential medium supplemented with 10% fetal calf serum. HeLa-O cells were maintained in McCoy's 5A medium (Hsu modified) supplemented with 5% calf serum. LLCMK2 (monkey kidney) cells were maintained in Eagle's minimum essential medium supplemented with 10% fetal calf serum. All media were purchased from Grand Island Biological Co., Grand Island, N.Y. For routine maintenance all cells except L …