Chapter 2: The immune system of the young horse

Question 1

What is the definition of the neonatal immune system?

Answer 1

“The neonatal immune system rapidly expands and generates appropriate immune responses to pathogens and environmental antigens.”

Question 2

What was previously believed about neonatal immunity?

Answer 2

“Neonates were previously not considered to be immunocompetent.”

Question 3

What have studies revealed about the immune responses of neonates?

Answer 3

“Studies of horse

Question 4

When does the lymphoid population of the thymus develop in the equine fetus?

Answer 4

“By approximately 80 days of gestation.”

Question 5

When are circulating lymphocytes observed in the equine fetus?

Answer 5

“By 120 days of gestation.”

Question 6

When are secondary lymphoid tissues populated in the equine fetus?

Answer 6

“Soon after circulating lymphocytes are observed.”

Question 7

What indicates successful B lymphopoiesis in fetal liver, bone marrow, and spleen tissues?

Answer 7

“Expression of transcripts for B cell genes like CD20

Question 8

What evidence is there for immunoglobulin isotype switching during mid-gestation?

Answer 8

“mRNA expression of IGHM

Question 9

What indicates the diversity of the immunoglobulin sequence content in equine fetuses?

Answer 9

“The significant increase in the variation between immunoglobulin transcripts and germline sequences between 100 days of gestation and birth.”

Question 10

What immunoglobulin proteins are evident in fetal serum before 200 days of gestation?

Answer 10

“Both IgM and IgG proteins.”

Question 11

What do low but detectable amounts of serum IgM and IgG at birth suggest?

Answer 11

“The fetal humoral immune system repertoire undergoes expansion and limited diversity in an antigen-independent manner during gestation.”

Question 12

What role does colostrum play in the neonatal immune system?

Answer 12

“Colostrum provides passive transfer of antibodies

Question 13

What soluble factors are provided by colostrum to the neonatal foal?

Answer 13

“Complement components (e.g.

Question 14

What is the timeline for IgG absorption from colostrum?

Answer 14

“Mares start producing colostrum a couple of weeks before foaling

Question 15

What are the primary immunoglobulin isotypes found in equine colostrum?

Answer 15

“Primarily IgG4/7

Question 16

What is the significance of passive transfer of immunoglobulins via colostrum?

Answer 16

“It provides essential humoral protection for foals

Question 17

What conditions may lead to failure of passive transfer (FPT) of immunoglobulins?

Answer 17

“Inadequate ingestion of colostrum

Question 18

How is failure of passive transfer (FPT) of immunoglobulins defined?

Answer 18

“Serum IgG concentration less than 800 mg/dL by 24 hours old

Question 19

What is the incidence rate of failure of passive transfer in foals?

Answer 19

“Estimated to be between 10–18% based on a serum IgG concentration below 400 mg/dL.”

Question 20

What are common causes of septicemia in neonatal foals?

Answer 20

“Respiratory

Question 21

What are the key components of the innate immune system in neonatal foals?

Answer 21

“Phagocytes

Question 22

How does the innate immune system function in neonatal foals?

Answer 22

“Newborn foals have intrinsic phagocytic and oxidative burst activities

Question 23

What is serum amyloid A (SAA) and its role in neonatal foals?

Answer 23

“An acute phase protein that induces chemotaxis

Question 24

What are Toll-like receptors (TLRs) and their role in the neonatal immune system?

Answer 24

“TLRs recognize pathogen-associated molecular patterns (PAMPs) and initiate immune cell activation; foal neutrophils express TLR-8 and TLR-9

Question 25

How do neonatal foal neutrophils respond to Toll-like receptor (TLR) stimulation?

Answer 25

"Foal neutrophils express pro-inflammatory cytokines like IL-6 and IL-8 upon TLR-8 stimulation

Question 26

What is the adaptive immune system's status at birth in foals?

Answer 26

"The adaptive immune system is naïve to environmental organisms but undergoes rapid expansion and maturation postnatally."

Question 27

What changes occur in the lymphocyte population of foals during the first five months of life?

Answer 27

"Circulating B and T lymphocyte populations expand in a linear fashion

Question 28

What is the significance of lymphocyte proliferation in neonatal foals?

Answer 28

"It reflects exposure to environmental antigens and pathogens

Question 29

What are age-dependent changes observed in foal antigen-presenting cells (APCs)?

Answer 29

"Reduced MHC class II expression in foals less than three months old

Question 30

When do foals develop organized lymphoid tissue in the lungs?

Answer 30

"Bronchus-associated lymphoid tissue (BALT) is observed by 12 weeks old

Question 31

What is the role of immunoglobulin A (IgA) in the mucosal immune system of foals?

Answer 31

"IgA offers effective neutralization and opsonization of pathogens and toxins

Question 32

When do foals start producing endogenous IgA in the respiratory tract?

Answer 32

"IgA is not detected in the airway until 28 days old

Question 33

What is the dynamic phase of circulating colostrum-derived antibodies and endogenous antibodies in foals?

Answer 33

"There is a nadir in total IgG observed between the first 1–2 months of life due to the decay of colostrum-derived antibodies and rise of endogenously-produced antibodies."

Question 34

How long does it take for foals to attain appreciable endogenous serum IgM and IgG levels?

Answer 34

"By 2–3 months of life

Question 35

What is considered adequate transfer of antibodies through colostrum at birth?

Answer 35

"A serum IgG level of at least 800 mg/dL

Question 36

When is endogenous production of immunoglobulin G4-7 (IgGb) observed in foals?

Answer 36

"IgG4-7 proteins are present in pre-suckle serum

Question 37

When does endogenous production of immunoglobulin E (IgE) occur in foals?

Answer 37

"Delayed until six months old

Question 38

What effect do passively transferred antibodies have on endogenous immunoglobulin production in foals?

Answer 38

"They may have a suppressive effect

Question 39

What cytokine production is observed in foal peripheral blood mononuclear cells (PBMCs)?

Answer 39

"Active production of TNF-alpha

Question 40

What immune responses do young foals generate to experimental infection and vaccine challenges?

Answer 40

"Antigen-specific humoral and cell-mediated immune responses

Question 41

What is the effect of vaccinating mares before foaling?

Answer 41

"Maximizes antigen-specific antibody transfer to the neonate through colostrum

Question 42

What are the challenges in neonatal vaccination?

Answer 42

"The need for immediate protection early in life with long-term memory

Question 43

What vaccination strategy has been effective against Rhodococcus equi in foals?

Answer 43

"Oral vaccination at two

Question 44

What are the implications of early exposure to environmental pathogens for neonatal foals?

Answer 44

"Exposure to pathogens before immune system priming can lead to disease