The interaction of infant formula with macrophages: effect on phagocytic activity, relationship to expression of class II MHC antigen and survival of orally administered macrophages in the neonatal gut.

The effect of infant formula on human peritoneal and breast milk macrophages has been investigated. The ability of peritoneal macrophages to subsequently ingest and degrade immune complexes was slightly impaired, but breast milk cells were not affected. However, the cells were found to have bound antigenically intact casein and beta-lactoglobulin, although little, if any, alpha-lactalbumin was bound. Furthermore, a positive correlation was found between binding of these proteins and expression of HLA-DR antigen. Labelled macrophages fed to newborn mice survived for at least 4 hr in the gastrointestinal tract and, in some cases, localized in the mucosal tissue. In one case a labelled cell was found in the spleen. These findings indicate that breast milk macrophages may be able to perform immunological functions in the gut, and suggest that binding of cows' milk proteins by macrophages may constitute a first step in the sensitization of the neonate to cow's milk proteins. Human milk macrophages may also play a protective role by acting as antigen-presenting cells in the local immune response of the gut.