13 Immunity in the Fetus and Newborn

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13 Immunity in the Fetus and Newborn
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13-1 Development of the Immune System

• The thymus is the first immune organ to develop.
• The development of secondary immune organs.
• B cells appear soon after the development of the
  spleen and lymph node, but antibodies are not
  usually found until late in fetal life.

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• The ability of the fetus to respond to antigens
  develops very rapidly after the immune organs
  appear, but all antigens are not equally capable
  of stimulating fetal response.
• The ability to mount cell-mediated immune
  responses develops almost simultaneously as
  antibody production.

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Calf

• The gestation period of the cow is 280d.
• The fetal thymus is recognizable by 40d
  postconception.
• The bone marrow and spleen appear at 55d.
• B cells work?
• Lymph nodes are found at 60d, but Peyers patches
  dont appear until 175d.

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Lamb

• The gestation period of the ewe is about 145d.
• MHC class I positive cells can be detected by 19d
  after sex service.
• MHC class II positive cells can be found by 25d.
• The thymus and lymph nodes are recognizable by
  35d and 50d, respectively. CD4 and CD8 cells
  appear in the thymus by 35 to 38d.

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Lamb

• Blood lymphocytes are seen by 32d.
• B cells are detectable at 48d in the spleen.
• The Peyers patches appear only at 60d.
• C3 receptors appear by 120d, but Fc receptors
  dont appear until the animal is born.

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Piglet

• The gestation period of the sow is about 115d.
• The first leukocyte can be found in the yolk sac
  and liver at 17d.
• The thymus develops by 40d postconception.
• The intestinal lymphoid tissues are devoid of T
  cells at birth.
• CD4T cell appear in the intestine at two weeks
  of age and CD8T cells at 4 weeks.

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• IgMB cells can be found in blood by day 50
  during the conception.
• NK cells dont develop until several weeks after
  birth.
• B cells can be found in the thymus of newborn
  piglets!!!
• The VDJ rearrangement is first seen in the fetal
  liver at 30d.
• IgM, IgA, and IgG transcripts are present at 50d.

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Chick

• 21-day of hatching eggs.
• Stem cells arise in the yolk sac membrane and
  migrate to the thymus and bursa at 5 to 7 days of
  incubation.
• IgM lymphocytes are detected in the bursa by day
  14. Antibodies are produced by 16 and 18d.
• IgY lymphocytes develop on day 21 around the
  time of hatching.
• IgA lymphocytes first appear in the intestine 3
  to 7 days after hatching.

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• Vaccination of 18-day embryonated eggs is
  commonly employed in the modern poultry industry.
• The major vaccine employed is against the Mareks
  disease herpesvirus.

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13-1-1 Development of Phagocytic Capability

• Neutrophils are fully capable of phagocytosing
  bacteria in the fetal pig at 90 days
  postconception.
• Poor bactericidal activity lasts until 100 days
  of pregnancy.
• Near birth, the phagocytic and bactericidal
  capacity of neutrophils declines as a result of
  fetal steroid levels.

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• After birth, macrophages have depressed
  chemotactic responsiveness, and they are also
  able to support the growth of some viruses.
• Newborn piglets is deficient in some complements.
• There are very few pulmonary macrophages in
  newborn piglets. They appear predominantly a few
  days later.

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13-1-2 The Immune System and Intrauterine
Infection

• The fetal immune system is less capable of
  combating infection.
• The acquired immune system is not fully
  functional.
• Some infections may be sever or lethal in the
  fetus.
• Bluetonge, infectious bovine rhinotracheitis,
  porcine parvovirus, bovine virus diarrhea, and
  brucella abortus.

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• Fetal infections commonly trigger an immune
  response and elevated Ig levels.
• The presence of any Ig in the serum of a newborn,
  unsuckled animal suggests infection in utero.

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The effects of bovine viral diarrhea virus
infection on development of the fetal calf depend
on the time of infection
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• Since they are specifically tolerant to BVD,
  persistently infected calves shed large
  quantities of virus in their body secretions and
  excretions and so act as the major source of BVD
  for other animals in a herd.
• The persistently infected calves grow slowly and
  often die of opportunistic infections, such as
  pneumonia before reaching adulthood.

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13-2 Immune Response of Newborn Animals

• Situation mammals are born into an environment
  rich in microorganisms after developing in the
  sterile environment in the uterus.
• The young of domestic animals are capable of
  mounting both innate and acquired immune
  responses at birth.
• The acquired immune system is in progress.

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• The newborn animals tend to produce immune
  responses skewed toward a Th2 rather than Th1
  cytokine pattern.
• Over the first months of life, the immune
  responses usually revert to the balanced adult
  pattern.
• Unless immunological assistance is provided,
  newborn animals may be killed by organisms that
  present little threat to an adult.

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13-3 Transfer of Immunity from Mother to
Offspring

• The rout by which maternal antibodies reach the
  fetus is determined by the structure of the
  placenta.

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13-3-1 Secretion and Composition of Colostrum
and Milk
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13-3-2 Absorption of Colostrum

• In pig, IgG and IgM are preferentially absorbed.
• In ruminants, all immunoglobulin classes are
  absorbed in the intestine.
• Permeability is highest immediately after birth
  and declines after about 6 hours.

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• In piglets, the ability of absorbing
  immunoglobulins may be retained for up to 4 days.
• The amount of IgA in the intestine can be large,
  a 3-week-old piglet may receive 1.6g daily from
  sows milk.

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13-4 Development of Acquired Immunity in
Neonatal Animals
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Local Immunity

• The intestinal lymphoid tissues of neonatal
  animals respond rapidly to an ingested antigen.
• Calves orally vaccinated with coronavirus
  vaccines at birth are resistant to virulent
  coronavirus within 3 to 9 days.

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• Piglets vaccinated orally 3 days after birth with
  transmissible gastroenteritis virus (TGE)
  vaccines develop neutralizing antibodies in the
  intestine 5-14 days later.
• There is an early intestinal IgM response that
  switch to IgA by 2 weeks.

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Systemic Immunity

• The maternal antibodies inhibit the ability of
  the newborn to mount its own immune response.
• Such an inhibition is B cell-specific and T cell
  responses are usually unaffected.
• One of the simplest is the rapid neutralization
  of live vaccines by the maternal antibody.
• The inhibition results from antibodies binding to
  B-cell Fc receptors and blocking BCR signaling.

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• Maternal antibodies simply mask the epitopes on
  vaccine antigens and so prevent their recognition
  by B cells.
• An immune response can be elicited only when
  maternal antibody titers fall below a critical
  threshold.

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• Calves begin to generate their own antibodies by
  about 1 week of age if they fail to suckle.
• If calves suckled and thus possess maternal
  antibodies, antibody synthesis does not commence
  until about 4 weeks of age.

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• In piglets, colostrum-deprived animals respond
  well to pseudorabies virus by 2 days after birth.
• If piglets suckled colostrum, antibody production
  does not begin until 5 to 6 weeks after birth.

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• Colostrun-deprived lambs generate IgG1 at 1 week
  and IgG2 by 3 to 4 weeks.
• In colostrum-fed lambs, IgG2 synthesis does not
  occur until 5 to 6 weeks old.

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Effect of the presence of maternal antibodies
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• The antibodies acquired by a young animal from
  its mother is called maternal antibody(????).
• Maternal antibodies is able to inhibit the
  ability of the newborn to mount its own immune
  responses.
• Very young animals are unable to respond to
  active immunization using vaccines.
• Such an inhibition is B-cell specific and T cell
  responses are largely unaffected.

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13-5 Vaccination of Young Animals

• Inhibition of maternal antibodies usually
  persists for a few months.
• Maternal antibodies absorbed from the puppys
  intestine reach maximal levels in serum by 12 to
  24 hours after birth.

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• The catabolic rate of the proteins is exponential
  and is expressed as a half-life.
• The half-life of antibodies to canine infectious
  hepatitis is 8.4 days.
• Very few newborn puppies can be successfully
  vaccinated.

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• Maternal antibodies to tetanus toxin in foals can
  last for 6 months, and antibodies to equine
  arteritis virus for as long as 8 months.
• Antibodies to bovine virus diarrhea may persist
  for up to 9 months in calves.
• The half-lives of maternal antibodies against
  equine influenza and equine arteritis virus
  antigens in the foals are 32 to 39 days.

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• Maternal antibodies effectively block immune
  response in young foals and calves, even at low
  levels, leading to ineffectiveness of premature
  vaccination.
• The effectiveness of vaccines increases
  progressively after the first 6 months of life.

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• BHV Bovine herpesvirus
• BVDV Bovine virus diarrhea virus

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• A safe rule is that calves and foals should be
  vaccinated no earlier than 3 to 4 months of age
  followed by one or two revaccinations at 4-week
  intervals.
• The precise schedule will depend on the vaccine
  used and the species to be vaccinated.
• Animals vaccinated before 6 months of age should
  always be revaccinated at 6 months or after
  weaning to ensure protection.

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13-6 Passive Immunity in the Chick

• Newly hatched birds emerge from the sterile
  environment of the egg and require temporary
  immunological assistance.
• Serum immunoglobulins are actively transported
  from the hens serum to the yolk while the egg is
  still in the ovary.
• IgM and IgA are acquired from oviduct secretions
  as the fertilized ovum pass down the oviduct.

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• As the chick embryo develops in ovo it absorbs
  the yolk IgY, which then appears in its
  circulation.
• IgM and IgA from the albumin diffuse into the
  amniotic fluid and are swallowed by the embryo.

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• A newly hatched bird has IgY in serum and, IgM
  and IgA in its intestine.
• The maternal antibodies effectively prevent
  successful vaccination until they disappear
  between 10 to 20 days after hatching.

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Take good care of our babies.
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Thank You!