Immune Benefits of Breastmilk at a Glance

White Blood Cells in Breastmilk

B LymphocytesGive rise to antibodies targeted against specific microbes.
MacrophagesKill microbes outright in the baby's gut, produce lysozyme and activate other components of the immune system.
NeutrophilsMay act as phagocytes, injecting bacteria in baby's digestive system.
T lymphocytesKill infected cells directly or send out chemical messages to mobilize other defenses. 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 response.

Molecules in Breastmilk

Antibodies of secretory IgA classBind to microbes in baby's digestive tract and thereby prevent them from passing through walls of the gut into body's tissues.
B12 binding proteinReduces amount of vitamin B-2, which bacteria need in order to grow.
Bifidus factorPromotes growth of Lactobacillus bifidus, harmless bacterium, in baby's gut. Growth of such nonpathogenic bacteria helps to crowd out dangerous varieties.
Fatty acidsDisrupt membranes surrounding certain viruses and destroy them.
FibronectinIncreases antimicrobial activity of macrophages; helps to repair tissues that have been damaged by immune reactions in baby's gut.
Gamma-interferonEnhances antimicrobial activity of immune cells.
Hormones and growth factorsStimulate baby's digestive tract to mature more quickly. Once the initially"leaky" membranes lining the gut mature, infants become less vulnerable to microorganisms.
LactoferrinBinds to iron, a mineral many bacteria need to survive. By reducing the available amount of iron, lactoferrin thwarts growth of pathogenic bacteria.
LysozymeKills bacteria by disrupting their cell walls.
MucinsAdhere to bacteria and viruses, thus keeping such microorganisms from attaching to mucosal surfaces.
OligosaccharidesBind to microorganisms and bar them from attaching to mucosal surfaces.

The table is from course notes by Robert J. Huskey, University of Virginia; adapted from an article in Scientific American.
Used by permission.
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