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From my understanding, our white blood cells 'learn' to fight off viruses and other pathogens that make us sick (or that they encounter because of vaccination) so that the subsequent encounters with same strain will not make us as sick; our immune system is able to fend off much better.

Newborns are protected with mother's antibodies via placenta and breast milk. My question is, can immunity be passed from mother to child via hereditary mechanisms, or does the child have a completely fresh set of 'default' defenses? Is that the reason why we get sick so easily when young?

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  • $\begingroup$ So what happens to bottle fed infants? $\endgroup$ – Graham Chiu Feb 22 '18 at 6:36
  • $\begingroup$ ^ that's something to ponder too $\endgroup$ – Gene Feb 22 '18 at 7:04
  • $\begingroup$ well, you have your answer. $\endgroup$ – Graham Chiu Feb 22 '18 at 8:12
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    $\begingroup$ (@GrahamChiu that's a comment - if you want to post it as an answer go ahead, but I suspect it might need more work...) $\endgroup$ – arboviral Feb 22 '18 at 10:02
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    $\begingroup$ Welcome to Biology.SE! It sounds like you've tried doing some research already and know something about adaptive immunity and maternal antibody transfer - can you include the sources you found so we can work out how much you already understand? (Showing how much research you've already done usually helps get positive responses, too.) $\endgroup$ – arboviral Feb 22 '18 at 10:06
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Newborn mammals get something called "passive immunity", in which the mother's antibodies are passed across to the fetus or newborn. Depending on the species, this can happen by the antibodies crossing the placenta, or more commonly by being transferred in the first milk the mother forms, "colostrum", which is very rich in antibodies. (At the same time, the newborn has special adaptations to absorb antibodies from the colostrum into its body; this only works for a short period after birth.)

This allows the newborn to have a temporary resistance to whatever pathogens happen to be common in its immediate environment (because presumably the mother would have been exposed to them). It's very much temporary, lasting typically a few weeks or so before the transferred antibodies half-life away. During this time, the newborn has a chance to start developing its own active immunity, which is dynamic and lasts much longer.

Edit to add:

Are there other modes of heritable immunity? Sort of but probably not what you're thinking of. Innate immune responses are often triggered through recognition of molecular patterns that are common to many different pathogens ("Pathogen-associated molecular patterns" or PAMPS). The receptors that recognize these patterns are inherited, and they are essential for starting innate immune responses which are in turn very important for starting acquired immune responses. So yes, every newborn mammal, and reptile, fish, sea urchin, arthropod, nematode, etc. inherits mechanisms for recognizing pathogens.

However, it's important to understand that these don't change during the mother's lifetime. This system doesn't provide any inheritance of recognition of pathogens that are locally important, or that the mother has met during her lifetime. This is the basic toolkit that every individual of the species (often, that every individual in the genus, or kingdom) has, that's needed to answer the general question "Is this a dangerous situation? Should I activate the immune response?"

In other words, as far as the innate system is concerned, "the child has a completely fresh set of 'default' defenses"; the only non-default information that's passed from mother to newborn is via the passive immunity described above.

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    $\begingroup$ I'm not sure this answers the question - it sounds like OP already knows something about maternal antibodies (("Newborns are protected with mother's antibodies via placenta and breast milk") but is asking whether other mechanisms for passing on immunity also exist. $\endgroup$ – arboviral Feb 22 '18 at 16:40
  • $\begingroup$ europepmc.org/articles/PMC3959733 $\endgroup$ – Graham Chiu Feb 22 '18 at 17:27
  • $\begingroup$ maybe this would be another question itself. U state that the receptors that recognize these patterns are inherited. but why would a mum that is vaccinated against a certain virus, would not pass that knowledge to the child? Since vaccination works by teaching the immune system to recognise the viral signature. Or this inherited immunity is for other kind of illnesses? $\endgroup$ – Gene Feb 23 '18 at 4:06
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    $\begingroup$ why would a mum that is vaccinated against a certain virus, would not pass that knowledge to the child -- She does, via the passive immunity I mentioned at the start. Why not pass down dynamic immunity? Probably because it's better to develop your own immunity to the pathogens you actually see yourself, rather than the ones your mother saw in 1962, or your great-great-grandfather saw in 1880. Passive immunity gives a brief coverage of possibly-relevant agents until you develop your own to the guaranteed-relevant ones. $\endgroup$ – iayork Feb 23 '18 at 10:49

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