# How do antibodies work? **URL:** \ **Category:** Factual Questions\ **Created:** [December 5, 2016, 5:39pm UTC](https://boards.straightdope.com/t/how-do-antibodies-work/773945 "2016-12-05T17:39:30Z")\ **Posts on this page:** 2\ **Page:** 2
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [December 7, 2016, 3:28am UTC](https://boards.straightdope.com/t/how-do-antibodies-work/773945/21 "2016-12-07T03:28:32Z")
[A more detailed answer](http://onlinelibrary.wiley.com/store/10.1034/j.1398-9995.2000.00118.x/asset/j.1398-9995.2000.00118.x.pdf;jsessionid=AF5C84CB424D024F9F4BFD7B0D499650.f03t04?v=1&t=iwechho8&8c3ecc88) than you may want. Most to the point of your questions: > [@](#): > > … B cells emerge into the peripheral circulation at 12 > weeks of gestation, and they are positive for CD19, > CD20, CD21, CD22, HLA-DR, IgM, and IgD (52). > The percentage of CD5+ B cells (B-1 B cells) is higher > in the fetal circulation than the adult, and declines > with increasing gestational age, yet even at birth most > cord-blood B cells are CD5+ (B-1 B cells), in contrast > to the adult, where few peripheral blood B cells > express this molecule (52, 53). CD5+ B cells are > largely T-independent, and CD5+ B cells produce > polyreactive antibodies which may have a role in the > primary immune response and be very useful in > the first line of defence, a necessary function in the > newborn … > > … Despite this early burst of production in fetal life, > the production of Ig isotypes at birth is impaired. > Neonates have very low serum IgM and even lower > IgA and IgE levels, and the IgG present is essentially > of maternal origin … The neonatal immune > system responds to a restricted array of antigens > producing largely IgM of low affinity … > > … As noted earlier (80), it is clear from the comprehensive > literature relating to domestic and experimental > animals that the principal stimuli of postnatal > maturation of the immune function in mammals are > signals from the microbial environment, particularly > the commensal microflora of the gastrointestinal tract. > Infections, particularly in the gastrointestinal and > respiratory tracts, may also contribute to this process … > In the absence of adequate microbial stimulation during infancy, the overall balance within the > adaptive immune system remains distorted toward > the Th2 phenotype, resulting in blunted expression of > Th1 immunity at peripheral challenge sites (82), a > failure of the immune deviation mechanisms that > normally regulate induction of Th2 responses at > mucosal surfaces (83), and excessive class switching of > immature B cells toward IgE commitment (84). … What happens depends on the pathogen and not just because of what is maturing immunologically but because of other changes as well. Think about the microcephaply that Zika causes as a prenatal infection while postnatally it is most often of no major consequence. Certain germs cause problems in different age groups and not others precisely because of the course of immunologic maturation. Did the mother pass on significant amounts of specific IgG to a particular bug? A large part of the infant response is based on that and on the innate system. What happens with some specific pathogens is described [here](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1418902/) if you want details. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 7, 2016, 4:04am UTC](https://boards.straightdope.com/t/how-do-antibodies-work/773945/22 "2016-12-07T04:04:13Z")
> [@Chronos](#): > > Oh, and > > Just what does “early in life” mean, here? Infancy? Prenatal fetal development? Approximately what age? > > And what happens if an infant/fetus/whatever is exposed to pathogens before this is done? Definitely pre-natal. I don’t know the exact timing. The “clonal deletion” of T- and B-cells that react to self-antigen takes place principally in the thymus, so it must be after that develops. The interesting thing, of course, is that many self-antigens are tissue-specific in their expression. I think the thymus expresses essentially every protein that’s present in any tissue in the body at this stage in order to expose the lymphocytes to all possible self antigens. Of course, autoimmune diseases are common, so this is presumably a complex and far-from-flawless process. It’s interesting that non-identical twins (with different MHC haplotypes) tend to be mutually tolerant of tissue grafts later in life. This implies that antigen-presenting-cells from one twin (i.e. with one twin’s MHC “encryption”) present self-antigen to the other twin’s T-cells during the period of clonal deletion. As for defense against infection prior to the immune system going “live”, i.e. in the early fetus, I don’t know. There’s another big complication in that the fetus has a different MHC haplotype to the mother, so as soon as antigen-presenting-cells in the fetus become active, they will be presenting self-antigens with a different “encryption key” that look like non-self to the mother’s immune system. So the placenta forms a barrier, supplemented by other mechanisms that prevent the mother’s immune system from attacking the fetus as though it were an incompatible tissue transplant. Some spontaneous miscarriages may be attributable to a failure in this barrier. > **[Immune tolerance in pregnancy](https://en.wikipedia.org/wiki/Immune_tolerance_in_pregnancy)** > > Immune tolerance in pregnancy or maternal immune tolerance is the immune tolerance shown towards the fetus and placenta during pregnancy. This tolerance counters the immune response that would normally result in the rejection of something foreign in the body, as can happen in cases of spontaneous abortion. It is studied within the field of reproductive immunology. > The placenta functions as an immunological barrier between the mother and the fetus, creating an immunologically privileged site. For... [Previous page](https://boards.straightdope.com/t/how-do-antibodies-work/773945.md?page=1)