Immuno 10 - Fetal and Newborn Immunity

Question 1

development of the immune system in the fetal calf

Answer 1

• The immune system is fully formed at birth but has never been used
  (under normal circumstances)
• Hence all adaptive immune responses in the newborn are slow primary responses
• Immune responses in utero are possible (which ones depends on stage of development)

Question 2

in utero infections

Answer 2

-Although fetuses can mount immune responses, they won’t be as effective as those of an adult

• This creates a scenario where the mother may get infected but remain clinically healthy, but the fetus suffers serious disease or even death
• Serum immunoglobulins in an un‐suckled newborn suggest that an in utero infection occurred (except for species such as primates, where there is transplacental transfer of Igs prior to birth)

Question 3

bovine viral diarrhea virus and fetal calf development

Answer 3

-The effects of bovine viral diarrhea virus infection on development of the fetal calf depend on the timing of infection. As with adult animals, there is considerable individual variation in resistance to infection. Persistently
infected calves may show minor neurological problems or failure to thrive.

Question 4

bovine viral diarrhea virus infection before/after calving

Answer 4

-Fetal infection can influence the
nature of disease when exposed to a
pathogen after birth.

-The relationship of mucosal disease
to persistent infection with bovine
viral diarrhea virus (BVDV) in tolerant
cattle.

-Calves persistently infected with
noncytopathic BVDV and then superinfected with cytopathic BVDV develop mucosal disease = a very
severe enteric infection with profuse
diarrhea and often death.

-The severity of disease is due to cross‐tolerance induced when the fetal immune system misinterpreted the noncytopathic form as self.

Question 5

intestinal microflora and the mucosal immune system

Answer 5

*In the absence of microflora, “germ‐free” mammals fail to fully develop mucosal‐associated lymphoid tissues (MALT)

*Commensal microflora generate PAMPs that activate host pattern recognition receptors

*Also, microbial antigens are taken up by dendritic cells and presented to CD4+ helper T cells

*Collectively, these signals promote the functional development of MALT

Question 6

rhodococcus equi; infection of foals

Answer 6

-An important disease in veterinary medicine

-Rhodococcus equi is ubiquitous in soil and bedding

-Newborn foals are exposed soon after birth

-A subset of foals are susceptible to this infection and develop severe pneumonia at a time when maternal antibodies are waning

-A combination of multiple immunological defects permits this otherwise innocuous organism to cause disease

-These defects may include an inappropriate or low repertoire of antibodies

Question 7

newborn animals and IgG

Answer 7

• Newborn mammals are temporarily
  protected against infection by transfer of immunoglobulins (Ig) from their mother
• Igs are derived from the mother either by direct transfer across the placenta as in primates, or by ingestion of immunoglobulin‐rich colostrum immediately after birth
• Colostrum is extremely important in
  species where the maternal Ig don’t cross the placenta (or overwhelming infections)

Question 8

differences in immunoglobulin classes in milk (ruminants vs non-ruminant)

Answer 8

• Relative concentrations of the major immunoglobulin classes in serum, colostrum, and the milk of ruminants and non‐ruminants
• IgG and IgA are the predominant isotypes in ruminant and non‐ruminant milk, respectively

Question 9

gut closure

Answer 9

• Gut closure: when the cells lining the gastrointestinal tract form tight junctions
• Until this happens, intact proteins,
  including systemically protective
  IgG, can directly transfer from the
  lumen of the GI tract into the blood
• Hence the reason for IgG being the
  predominant isotype in colostrum
• Note: gut closure generally occurs
  later in colostrum‐deprived animals

Question 10

importance of transfer of passive immunity

Answer 10

-Clostridium perfringens antitoxin levels in serum, colostrum, and milk of six pony mares and in the serum of their foals from birth to five months

• Colostrum intake (short‐ term) is required to protect young animals against septicemic disease
• Milk provides a constant supply of immunoglobulin (IgA in nonruminants; IgG in ruminants) for long‐ term protection of the gastrointestinal tract against enteric infection

Question 11

contributions of maternal vs neonatal antibodies (passive vs active immunity)

Answer 11

Immunoglobulin levels in newborn serum during the first 15 weeks of life, indicating the contributions of maternal antibodies and antibodies synthesized by the neonate

Question 12

two tests of passive transfer in horses

Answer 12

-snap test
-turbidimetric immunoassay

Question 13

zinc sulphate turbidity test

Answer 13

-A zinc sulphate solution can cause serum globulins, especially immunoglobulins, to precipitate
out of serum. The resultant turbidity is proportional to the Ig concentration and may be quantitated using a standard curve based on optical density. This test provides a crude but rapid estimate of serum Ig and is used, for example, to evaluate passive transfer of IgG from dam to offspring (the more turbid the solution, the more IgG there is)

Question 14

managin failure of passive transfer

Answer 14

Failure of passive transfer can be due to:
1. Insufficient immunoglobulin concentrations in the colostrum
2. Failure to ingest the colostrum
3. Failure to absorb the colostrum

-Can test for passive transfer after birth (i.e., need to wait until antibody
absorption is normally complete)

-Low antibody concentration: watch very closely and treat with antibiotics
at the first sign of infection (early intervention)

-Very low antibody concentrations or complete failure of passive transfer:
intensive feeding of an alternative source of colostrum (from donor
mares or commercially available products)

-If no colostrum available, give higher doses of plasma or serum

-If gut absorption is no longer feasible, plasma would have to be given intravenously

Question 15

timing of vaccines for neonates is very important

Answer 15

-Maternal antibodies provide critical
protection in the days after birth when the neonatal immune system is naïve.

-They also inhibit the production of
antibodies by the neonate’s own B cells (remember the negative feedback regulation mediated by the inhibitory CD32 Fc receptor on B cells from lecture #9) or may directly neutralize the vaccine (if the maternal antibodies are specific for the vaccine vector).

-This means that vaccines given too early (i.e., when maternal antibody titers are high) will result in poor B cell responses in the neonate.

-It is best to wait until maternal antibody titers are low (but don’t wait too long or the neonate is left unprotected)

-Effect of the presence of maternal antibodies to canine parvovirus in 653 puppies on their response to a modified live parvovirus vaccine.
-Pre‐vaccination antibody titer profoundly inhibits the response of the puppies to the vaccine

Question 16

what is vaccine efficacy affected by

Answer 16

-Effectiveness of two inactivated viral vaccines in calves between birth and six months of age.

-BHV‐1 = bovine herpes virus‐1
-BVDV = bovine viral diarrhea virus

Question 17

recommendation for neonatal vaccines

Answer 17

• Nomographs showing the relationship between the antibody titer of the mother and the age at which to vaccinate her offspring with modified live virus vaccine
• Testing antibody titers in mothers
  and then timing vaccination on this
  basis is very accurate but often not
  practical, especially in production
  animal settings
• Therefore, general recommendations are typically provided by vaccine manufacturers based on a large body of accumulated data

Question 18

passive immunity in chicks

Answer 18

-Newly hatched birds emerge from the sterile environment of the egg and, like mammals, require temporary immunological assistance

-Serum immunoglobulins are actively transported from the hen’s serum to the yolk while the egg is still in the ovary

-IgY in the fluid phase of egg yolk is therefore found at levels equal to or greater than those in hen serum
In addition, as the fertilized ovum passes down the oviduct, IgM and IgA from oviduct secretions are acquired with the albumin

-Embryonic chicks absorb 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. When a chick hatches, it possesses IgY in its serum and IgM and IgA in its intestine

-Yolk sac antibodies aren’t fully absorbed until 24 hours post‐hatch

-Maternal antibodies prevent successful vaccination until they disappear (10‐20 days post‐hatch)

Question 19

neonatal isoerythrolysis in foals

Answer 19

• A condition in which a mare creates antibodies against her foal’s red
  blood cells and then passes them to the foal via colostrum (can’t cross the placenta)
• When the foal absorbs these antibodies, they lyse the red blood cells within 24‐36 hours after birth
• Causes life‐threatening anemia and/or jaundice
• The mare must have had previous exposure to blood that contained
  the target antigen (e.g., a blood transfusion or a previous foaling)
• Affected foals will develop progressive anemia, leading to depression, anorexia, collapse, and death
• Other signs may include development of pale mucous membranes that later become yellow, or jaundiced
• If neonatal isoerythrolysis is suspected in a foal that is less than 24 hours old, further ingestion of the mare’s colostrum must be prohibited
• This foal should be fed an alternative source of colostrum
• Foals that are over 24 hours old when suspected to be suffering from neonatal isoerythrolysis may need to undergo a blood transfusion in order to save their life
• Prevention is more effective than treatment
• Mares at risk of producing a foal with NI have previously had an NI foal or have blood samples that are positive for antibodies to the Aa and/or Qa blood antigens
• Standardbreds and Thoroughbreds have an increased incidence of NI foals
• Colostrum from a NI‐producing mare should never be used or saved
• Alternative sources of colostrum should be acquired prior to parturition for cases where an NI foal is likely

Question 20

tests for neonatal isoerythrolysis in foals

Answer 20

• Tests that can be used to detect/predict NI:
  –>direct Coombs test
  –>indirect Coombs test
• Both tests are named after Robin Coombs 1921‐2006, a British immunologist, and use ‘Coombs reagent’ (immunoglobulin‐specific and complement protein‐specific antibodies)

Question 21

direct coombs test

Answer 21

(also called ‘direct antiglobulin test’ [DAT]):

• To diagnose immune‐mediated hemolytic anemia
• A single‐step test used to detect erythrocyte‐specific antibodies and/or complement proteins that are bound to the surface of red blood cells
• A blood sample is taken from a foal suspected of NI, and the RBCs are washed (removing the patient’s own plasma) and then incubated with
  Coombs reagent (for NI, the antibodies would be horse‐specific)
• If RBCs agglutinate, the direct Coombs test is positive; a visual indication that antibodies and/or complement proteins are bound to the surface of RBCs (i.e., the patient has immune‐mediated hemolytic anemia)

1) patients red blood cells are washed and diluted 1:2 in isotinic saline
2) coombs reagent: anti-dog IgM and anti-dog IgG and anti-dog C3 is mixed with the RBCs
3) if there are antibodies or complement on the surface of RBCs, the cells will agglutinate

Question 22

indirect coombs test

Answer 22

-A two‐step test that could be done prior to feeding colostrum (to prevent NI)

-Detects serum‐derived antibodies against RBCs

-Step 1: serum is extracted from a blood sample from the mare and incubated with RBCs from the foal

-Step 2: the Coombs reagent is added
If agglutination occurs, the indirect Coombs test is positive and the mare’s colostrum should not be fed to the foal