Senescence

Inclusion of vitamin E (DL-alpha-tocopherol) in the culture medium for human diploid cells greatly prolongs their in vitro lifespan. The addition of 100 mug of DL-alpha-tocopherol per ml of medium has allowed us to culture WI-38 cells for more than 100 population doublings to date. (These cells normally have an in vitro lifespan of 50 +/- 10 population doublings.) Cells at the 100th population doubling have a normal diploid karyotype, appear to behave in all other respects like young WI-38 cells, and are still actively dividing.

It has been shown that human diploid cells from various donor ages can be arrested in an essentially nonmitotic state by reducing the serum concentration of the incubation medium from 10 to 0.5 percent. Cells incubated at this serum level maintained the population distribution that was present when the cells reached confluency. The population, which has 90 percent of the cells in the G1 phase of the division cycle, was not static and exhibited a low level of mitotic activity with prolonged interdivision times.

Of all the theories purporting to uncover the roots of childhood behaviour and its extension into adult behaviour, the most cogent relates to the physical and psychological bonds of attachment between infant and mother. It is helpful to divide the human lifespan into three periods, each of which has alternating phases of attachment and detachment.

Previously we reported [Packer, L. & Smith, J.R. (1974) Proc. Natl. Acad. Sci. USA 71, 4763-4767] that the lifespan of WI-38 human diploid fibroblasts in vitro was significantly increased by continuously growing the cell cultures in the presence of vitamin E(dl-alpha-tocopherol), but in 19 subsequent subcultivation series we were unable to reproduce these findings. While vitamin E is incorporated into the cells and is able to act effectively as an antioxidant, apparantly is intracellular antioxidant properties alone do not routinely result in an increase of cell lifespan.

Various concentrations of oxygen were used to determine the optimum culture medium PO2 for survival and proliferation of attached human and mouse fibroblasts grown from different inoculum sizes. When T-15 flasks were seeded with less than or equal to 2 X 10(4) cells (less than or equal to 1.3 X 10(3) cells/cm2), the highest plating efficiencies and cell yields were obtained with a culture medium PO2 of 40-60 mm Hg.

Ageing in immune reactivity is described at the level of lymphoid cells, at that of lymphoid organs and organ function, and at that of regulation of cell and organ function. Apart from shifts in numbers of lymphoid cell subpopulations, the decrease in communication capacity between lymphoid cell populations and in binding of invaders (like bacteria) is an important aspect of ageing. These aspects may contribute to the decreased immune reactivity to invaders and the enhanced incidence of immune reactions to self-components (autoimmune reactivity).

Normal human diploid cells, TIG-1, ceased to proliferate at about the 62 population doubling level (PDL). Transformed clones isolated from TIG-1 cells infected with wtSV40 and those with tsA900 SV40 cultured at 34 degrees C were subcultured up to about 80 PDL. When the culture temperature of tsA SV40-transformed cells was shifted from 34 to 39.5 degrees C at 51 PDL, the growth curve of these transformed cells changed to that of normal young cells.

An extension of the mathematical model of immunological tolerance including two categories of B and T helper cells, each having a different lifespan, is presented. The simulated recovery from tolerance is compared with experimental data on B and T helper cell tolerance to human gamma globulin (HGG) induced in adult mice. The performed simulation runs suggest the conclusion that in this case it seems impossible to incorporate a high ratio of both, long-lived B cells and/or short-lived T helper cells, if good agreement with the available experimental data should be preserved.

Dermal fibroblasts from patients with the autosomal dominant cancer-prone disease Basal Cell Nevus Syndrome (BCNS) exhibit a serum dependence, anchorage dependence and in vitro lifespan (about 20 population doublings or less) similar to those of fibroblasts from normal age-, race- and sex-matched controls.

Tumor-promoting phorbol esters, like growth factors, elicit pleiotropic responses involving biochemical pathways that lead to different biological responses. Genetic variant cell lines that are resistant to mitogenic, differentiation, or transformation responses to tumor promoters have been valuable tools for understanding the molecular bases of these responses.