Properties of a macrophage cell line transformed by simian virus 40. Morphological changes related to cell functions

Induction of fibronectin expression, actin cable formation, and entry into S phase following reexpression of T antigen in mouse macrophages transformed by the tsA640 mutant of SV40

Mouse macrophages transformed by a temperature-sensitive mutant (tsA640) of simian virus 40 (SV40) were examined by immunofluorescence microscopy for fibronectin expression and actin distribution. Resting cultures of tsA640 transformants incubated at a temperature nonpermissive for SV40 large T antigen (39.0 degrees C) exhibited phagocytic activity and did not exhibit cellular fibronectin and actin cables, like primary cultures of resident macrophages. When the resting cultures were sparsely seeded and shifted down to the permissive temperature of 33.0 degrees C, expression of large T antigen in the nucleus, expression of fibronectin in the cytoplasm, and cellular entry into S phase occurred in that temporal order, followed by actin cable formation, cellular proliferation, and diminishment of phagocytic activity. The expression of T antigen and fibronectin was sensitive to actinomycin D and cycloheximide. The expression of fibronectin was insensitive to inhibitors of DNA synthesis, whereas the expression of actin cables was sensitive. These results suggest that SV40 T antigen leads macrophages to express fibronectin and actin cables, as well as resumption of cell proliferation, and that entry into S phase is not required for fibronectin expression but may be required for actin cable formation.

Phenotypic change of an SV40-transformed mouse macrophage line, BB-W-531-2 induced by different cultural methods

A simian virus 40 (SV40)-transformed macrophage clone which was established from BALB/cAnN mouse bone marrow cells was used to study the effect of different cultural conditions on the expression of macrophage properties. The macrophage clone, BB-W-531-2 line, expressed and maintained the macrophage properties, immune phagocytosis of Fc- and complement receptors, under the growth-inhibiting conditions of confluent density and of cultivation on bacteriologic dishes with reduced adhesiveness. However, the cells lost their ability to express the macrophage properties dependent upon cell density after repeated culture splits in the growing phase. These cells regained that ability when they were cocultured with cells having macrophage properties. These results suggest that there is a possible correlation between reduced multiplication and the expression of macrophage properties, and that macrophage properties which have been suppressed or blocked may be induced by diffusible factor(s) produced by macrophages.

Production of interferon by an SV40-transformed macrophage line, BB-W-531-2

A simian virus 40-transformed mouse macrophage line, BB-W-531-2, was examined for its ability to produce interferon. BB-W-531-2 cells showed a phenotypic change between the macrophage and the nonmacrophage states. A viral inhibitor (interferon) was produced by the cells during the phenotypic change from the nonmacrophage to the macrophage state. Cells having macrophage properties were well capable of producing interferon when they were stimulated with ultraviolet-inactivated vaccinia virus, lipopolysaccharide, a streptococcal preparation (OK-432) or polyinosinate . polycytidylate. In contrast, cells that had lost their macrophage properties did not produce interferon even when they were given the same treatments as the cells having macrophage properties. The results suggest that the ability of BB-W-531-2 cells to produce interferon is associated with the expression of several macrophage properties.