In response to Kathy Dettwyler and Paul Zimmer:

I too am struggling to understand the maturation of the infant's immune
system.  When I took all my immunology classes almost 20 years ago, there was
little discussion about this topic.  Production of infant antibodies was
documented within the first 6 months after birth, as the concentration of
maternal antibodies decreased in the infant, and didn't reach adult levels
until later childhood/puberty - but that's all I remember from my graduate
studies.  Armond Goldman has a pertinent table in his 1993 paper "The immune
system of human milk: antimicrobial, antiinflammatory and immunomodulating
properties" (Pediatr Infect Dis J. 1993; 12:664-71).  In this table he lists
the approximate times of maturation of infant immune factors: secretory IgA
at 4 - 12 months, full antibody repertoire at 24 months, lysozyme at 1 - 2
years, and memory T cells at 2 years.  Ranges of maturation for individual
factors are apparently due to varying results found in different studies.

I've also found the following two articles useful in describing development
of the immune system: Fitzsimmons et al. ("Immunoglobulin A subclasses in
infants' saliva and in saliva and milk from their mothers." J. Pediatr.
1994;124:566-73) illustrates the maturation rates of subclasses of antibodies
at different sites (e.g. serum and saliva); and Brandzaeg et al. ("Ontogeny
of the mucosal immune system and IgA deficiency." Gastroenterology Clinics of
No. America 1991; 20:397-39) has an excellent review of the development of
the infant mucosal immune system.  And I have several articles which discuss
the probable enhancement of the production of isolated infant immune factors
by breastfeeding within weeks of birth.

I'm not sure what the TIME article referred to when it said "A newborn's
immune system isn't fully functional until around 18 months...."  (Which
issue is this from? I'm hopelessly behind in my reading.)  And what does
"fully functional" mean?  I doubt this quote, though, even if documented,
would have much of an effect on those US physicians who claim that immunities
in breast milk are insignificant after "X" amount of time.  Most/many (some?)
children in this country have access to clean water, adequate food, and
antibiotics which keep them reasonably healthy in spite of immature immune
systems. It is difficult to show in the US that human milk has a significant
effect on infectious diseases in older children - especially when it is so
hard to find significant numbers of children breastfeeding over 12 months who
can participate in meaningful studies.

I'd love to see what anyone else has to share on this topic.
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Marty O'Donnell, PhD     [log in to unmask]
Park Ridge, Illinois