Iron requirements of human lymphocytes: relative contributions of intra- and extra-cellular iron

A supply of iron is of vital importance if lymphocyte proliferation is to proceed successfully and two major sources of iron are available, intracellular stores and serum transferrin. We have investigated the relative importance to the human T lymphocyte of these two sources of iron by depleting them of intracellular iron with the chelator desferrioxamine and by culturing them in medium completely depleted of transferrin iron. The chelator decreased mitogen-stimulated proliferation of human peripheral blood T cells, in a dose-dependent manner, in the absence of extracellular transferrin-iron. By culturing the cells in iron-depleted medium, we found that normal lymphocytes proliferated, to a degree, in the absence of extracellular transferrin-iron. We also observed that transferrin receptor mRNA expression was sustained in mitogen-stimulated, iron-deprived lymphocytes, compared with untreated cells suggesting that up-regulation of transferrin receptor may occur in these cells through stabilization of the mRNA. We propose that intra- and extra-cellular iron may contribute to early and late activation processes and that a low level of intracellular iron in lymphocytes, chronically activated in the iron-deficient environment associated with chronic inflammatory diseases such as rheumatoid arthritis, may be a factor in the abnormal cell-mediated immunity associated with such diseases.