Proteomics as a tool to explore human milk in health and disease

Proteins in milk have wide range of functions, they are carriers of minerals or chemically vulnerable and insoluble vitamins and other compounds, stabilisers of large aggregates or micelles of lipids, and components of both innate and acquired immune defence systems. Together with other components of milk, proteins may also contribute to the selection and establishment of appropriate microbiome in the gut of the infant. The proteome of mammalian milk is now known to be dynamic and changes radically with time after birth from colostrum to mature lactation. Significantly, immune and innate defence proteins appear in milk during infection of the mammary gland and possibly also during systemic infections. The understanding of the human milk proteome and how it changes with time during lactation and in disease is developing rapidly, and is to a large extent informed by proteomics of the milks of non-human mammals, domestic animals in particular. We review general methods now being applied for proteomic analysis of human milk. Moreover we place emphasis on how the milk proteome may change in different ways in response to disease, mastitis in particular, how such changes may be specific to pathogen types, and we give some insights about evolution.