Proliferative capacity of human fibroblasts when cultured in serum from young or old cows

Diploid human fibroblasts have a limited proliferative capacity when grown in vitro, leading to senescence and eventual death of the culture. Results of earlier work suggested that serum from older animals might contain higher concentrations of growth inhibitors that could accelerate the onset of cellular senescence. To reexamine this question, we cultured human MRC-5 cells in bovine fetal calf serum and in serum from cows of various ages. Surprisingly, we found that human MRC-5 cells, which are normally cultured in bovine fetal calf serum, exhibit nearly identical proliferative capacity when grown in serum from young or old cows. Our failure to detect significant differences in the proliferative capacity of MRC-5 cells cultured in serum from cows of widely different ages suggests that the balance of growth-stimulating and growth-inhibiting factors in serum does not vary significantly as a function of animal age.