Immune Benefits of Breastfeeding at a Glance

B lymphocytes: Give rise to antibodies targeted against specific microbes
Macrophages: Kill microbes outright in the baby's gut, produce lysozymes and activate other components of the immune system
Neutrophils: May act as phagocytes, ingesting bacteria in the baby's digestive system
T lymphocytes: Kill infected cells directly or send out chemical messages to mobilize other defences. They proliferate in the presence of organisms that cause serious illness in infants. They also manufacture compounds that can strengthen a child's own immune system.

Antibodies of secretory IgA class: Bind to microbes in the baby's digestive tract and thereby prevent them from passing through walls of the gut into the body's tissues
B12 binding protein: Reduces amount of vitamin B12, which bacteria need in order to grow
Bifidus factor: Promotes growth of Lactobacillus bifidus, a harmless bacterium, in baby's gut. Growth of such nonpathogenic bacteria helps to crowd out dangerous varieties
Fatty acids: Disrupt membranes surrounding certain viruses and destroy them
Fibronectin: Increases antimicrobial activity of macrophages; helps to repair tissues that have been damaged by immune reaction inthe baby's gut.
Gamma-interferon: Enhances antimicrobial activity of the immune cells
Hormones and growth factors: Stimulate the baby's digestive tract to mature more quickly. Once the initial "leaky" membranes lining the gut mature, infant become less vulnerable to microorganisms.
Lactoferrin: Binds to iron, a mineral many bacteria need to survive. By reducing the available amount of iron, lactoferrin thwarts growth of pathogenic bacteria
Lysozyme: Kills bacteria by disrupting their cell walls
Mucins: Adhere to bacteria and viruses, thus keeping such microorganisms from attaching to mucosal surfaces
Oligosaccharides: Bind to microorganisms and bar them from attaching to mucosal surfaces