The effect of lactoferrin (Lf) on mammary epithelial cell growth in cu
lture was tested in a comparative study of bovine and human Lf. Bovine
Lf was inhibitory to growth of a bovine mammary epithelial cell line,
both in the presence and absence of fetal bovine serum in the medium.
The growth inhibition activity of bovine Lf was not affected by iron-
saturation status of the protein. In contrast with bovine Lf, human Lf
had minimal inhibitory activity on bovine cell growth in the presence
of serum, and cell growth was stimulated by human Lf in the absence o
f serum. In the latter case, human Lf may have acted as an iron-transp
ort protein for the cells. Bovine Lf and human Lf had no effect on gro
wth of MCF-7 human breast tumor cells and only minimal inhibitory acti
vity toward the MDA-MB 231 human breast tumor cell line. The effect of
bovine Lf on bovine mammary epithelial cells could be prevented by im
munoneutralization of the Lf. These results indicate that Lf can be in
hibitory to growth of mammary epithelial cells in culture, but this re
sponse is specific for the species origin of the Lf and of the mammary
cell.