Proteomics reveals new evolving roles in defense and development from colostrum to mature milk

Human milk proteins provide nutrition and support a number of vital biological processes in nursing infants. In‐depth understanding of the functions of human milk proteins has been inhibited by incomplete knowledge of the human milk proteome. We analyzed the proteomes of whey protein from human colostrum (first week; n=3) and corresponding mature milk (3 mo) using both ion‐exchange and SDS‐PAGE based protein fractionation methods. We found that the immunoglobulins sIgA and IgM are upregulated in colostrum whereas IgG is upregulated in mature milk, indicating a transformation in defense mechanism from newborns to young infants. A comprehensive view of complement components and complement regulatory proteins points to an essential role for the milk complement system prevailed by alternative pathway compared to classical pathway. A number of extracellular matrix (ECM) proteins are upregulated in colostrum. In contrast, ECM protein, fibronectin, and several actin cytoskeleton proteins it regulates are more abundant in mature milk that may underlie the important functional role of milk in regulating reactive oxygen species. The research is supported by Mead Johnson Nutrition and NIH HD 13021.