By now several studies have provided evidence that breastfeeding provides enhanced protection against infection also for years after the termination ofbreastfeeding49. This has been suggested for otitis media53, respiratory tract infections54 Haemophilus influenzae type b infections55-56, diarrhoea57 and wheezing bronchitis in non-atopic children58, 59, This enhanced protection may last from 3-10 years and the protection seems to be increased foreachweekof breastfeeding.
There is also evidence that vaccinations may be enhanced during and after breastfeeding against e.g. BCG60,tetanus and diphteria toxoids and poliovirus vaccines61. However, this effect is not seen against all vaccines whichhasbeen discussed49.
Studies of the mechanisms behind this indicate that anti-idiotypic antibodies and lymphocytes from the mother's milk are taken up in the infant's gut and can obviously prime its immune system. Anti-idiotypes given to neonatal mice via the milk clearly primes, enhancing subsequent immune responses6263 .
Anti-idiotypic antibodies are present in human milk and might have a similar effect64.
Several studies indicate that milk lymphocytes are taken up and found in the gut mucosa, mesenteric lymph nodes and even in small numbers in spleen and lungs65-69. Quite remarkable is that the offspring becomes tolerant to the maternal MHC thus becoming able to accept these milk cells which then might be able to transfer immunological information. One striking consequence is that this tolerance to maternal MHC results in significantly better results of renal transplantation using the mother as the donor and the child (even as an adult) as a recipient. The results are much better than if the donor is the father or a mother who has notbreastfed70-72. In agreement with this breastfed children have a significantly lower precursor frequency of cytotoxic T lymphocytes reactive against maternal HLA than non breastfed73.
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For many years, scientists have been playing out the ingredients that make breast milk the perfect food for babies. They've discovered to day over 200 close compounds to fight infection, help the immune system mature, aid in digestion, and support brain growth - nature made properties that science simply cannot copy. The important long term benefits of breast feeding include reduced risk of asthma, allergies, obesity, and some forms of childhood cancer. The more that scientists continue to learn, the better breast milk looks.