Presence of macrophagemigration inhibitory factor in human milk: evidence in the aqueous phase and milkfat globules.

Human milk is a source of bioactive substances regulating the development and activity of the newborn immune system. Human milk has been found to contain a number of cytokines, including interleukins, growth factors, and colony stimulating factors. In the present study, we assessed 10 specimens of human milk for the presence of macrophage migration inhibitory factor (MIF), a cytokine recently described in several human reproductive organs and tissues. Using biochemical as well as immunologic techniques, we showed that MIF is abundantly present in human milk, mostly distributed in the lipid layer and in the aqueous phase. Fractionation of the lipid layer showed that MIF is highly concentrated inside milk fat globules. In view of its proinflammatory features, we speculate that milk MIF may protect the newborn against infection and play a role in preserving the functionality of the lactating mammary gland. Furthermore, the localization of MIF in lipid globules suggests a possible strategy for the protection of milk cytokines from the gastric barrier.