Lactoferrin: no evidence for its role in regulation of CSA production by human lymphocytes and monocytes.

Lactoferrin (LF) has been recently proposed as a physiologic regulator of the granulocyte monocyte progenitor (CFU-GM). This glycoprotein, when saturated with iron, has been said to limit CFU-GM growth by decreasing production and release of colony stimulating activity (CSA) by monocytes and macrophages. Human milk LF saturated with iron, at concentrations ranging from 10(-18) to 10(-8) M was added either to endogenously stimulated bone marrow cells or to mononucleated cells used as feeder layers for adherent cell-depleted marrow. Irrespective of the concentration of LF within the culture system used, no significant inhibition of CFU-GM growth was observed. Moreover, the CFU-GM stimulating activity of medium conditioned by a 4-day incubation of 1 X 10(6) mononucleated blood cells in the presence or in the absence of LF was the same. Various possible explanations for not confirming the reported inhibiting activity of iron saturated LF were explored: 1) masking inhibition of the system by prostaglandin E2 (PGE2), 2) masking inhibition of the system by bovine LF still detectable in the fetal calf serum after heating, 3) preinhibition of the system by leukemic-associated inhibitory activity (LIA) possibly present in the culture system, 4) the iron and calcium content of the culture medium used, 5) the fixation of LF to plastic compounds, 6) the source of the human LF used, 7) the marrow cell separation methods used. None of these factors was shown to play a role in vitro in the activity of LF and thus no evidence was found for a significant role of LF in the regulation of CSA production by monocytes. Peripheral blood human monocytes isolated by elutriation and incubated in albumin free medium in the presence of either 125I-LF or colloidal gold-labeled LF showed no LF binding.