Chapter 2: The immune system of the young horse Flashcards
What is the definition of the neonatal immune system?
“The neonatal immune system rapidly expands and generates appropriate immune responses to pathogens and environmental antigens.”
What was previously believed about neonatal immunity?
“Neonates were previously not considered to be immunocompetent.”
What have studies revealed about the immune responses of neonates?
“Studies of horse
When does the lymphoid population of the thymus develop in the equine fetus?
“By approximately 80 days of gestation.”
When are circulating lymphocytes observed in the equine fetus?
“By 120 days of gestation.”
When are secondary lymphoid tissues populated in the equine fetus?
“Soon after circulating lymphocytes are observed.”
What indicates successful B lymphopoiesis in fetal liver, bone marrow, and spleen tissues?
“Expression of transcripts for B cell genes like CD20
What evidence is there for immunoglobulin isotype switching during mid-gestation?
“mRNA expression of IGHM
What indicates the diversity of the immunoglobulin sequence content in equine fetuses?
“The significant increase in the variation between immunoglobulin transcripts and germline sequences between 100 days of gestation and birth.”
What immunoglobulin proteins are evident in fetal serum before 200 days of gestation?
“Both IgM and IgG proteins.”
What do low but detectable amounts of serum IgM and IgG at birth suggest?
“The fetal humoral immune system repertoire undergoes expansion and limited diversity in an antigen-independent manner during gestation.”
What role does colostrum play in the neonatal immune system?
“Colostrum provides passive transfer of antibodies
What soluble factors are provided by colostrum to the neonatal foal?
“Complement components (e.g.
What is the timeline for IgG absorption from colostrum?
“Mares start producing colostrum a couple of weeks before foaling
What are the primary immunoglobulin isotypes found in equine colostrum?
“Primarily IgG4/7
What is the significance of passive transfer of immunoglobulins via colostrum?
“It provides essential humoral protection for foals
What conditions may lead to failure of passive transfer (FPT) of immunoglobulins?
“Inadequate ingestion of colostrum
How is failure of passive transfer (FPT) of immunoglobulins defined?
“Serum IgG concentration less than 800 mg/dL by 24 hours old
What is the incidence rate of failure of passive transfer in foals?
“Estimated to be between 10–18% based on a serum IgG concentration below 400 mg/dL.”
What are common causes of septicemia in neonatal foals?
“Respiratory
What are the key components of the innate immune system in neonatal foals?
“Phagocytes
How does the innate immune system function in neonatal foals?
“Newborn foals have intrinsic phagocytic and oxidative burst activities
What is serum amyloid A (SAA) and its role in neonatal foals?
“An acute phase protein that induces chemotaxis
What are Toll-like receptors (TLRs) and their role in the neonatal immune system?
“TLRs recognize pathogen-associated molecular patterns (PAMPs) and initiate immune cell activation; foal neutrophils express TLR-8 and TLR-9
How do neonatal foal neutrophils respond to Toll-like receptor (TLR) stimulation?
“Foal neutrophils express pro-inflammatory cytokines like IL-6 and IL-8 upon TLR-8 stimulation
What is the adaptive immune system’s status at birth in foals?
“The adaptive immune system is naïve to environmental organisms but undergoes rapid expansion and maturation postnatally.”
What changes occur in the lymphocyte population of foals during the first five months of life?
“Circulating B and T lymphocyte populations expand in a linear fashion
What is the significance of lymphocyte proliferation in neonatal foals?
“It reflects exposure to environmental antigens and pathogens
What are age-dependent changes observed in foal antigen-presenting cells (APCs)?
“Reduced MHC class II expression in foals less than three months old
When do foals develop organized lymphoid tissue in the lungs?
“Bronchus-associated lymphoid tissue (BALT) is observed by 12 weeks old
What is the role of immunoglobulin A (IgA) in the mucosal immune system of foals?
“IgA offers effective neutralization and opsonization of pathogens and toxins
When do foals start producing endogenous IgA in the respiratory tract?
“IgA is not detected in the airway until 28 days old
What is the dynamic phase of circulating colostrum-derived antibodies and endogenous antibodies in foals?
“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.”
How long does it take for foals to attain appreciable endogenous serum IgM and IgG levels?
“By 2–3 months of life
What is considered adequate transfer of antibodies through colostrum at birth?
“A serum IgG level of at least 800 mg/dL
When is endogenous production of immunoglobulin G4-7 (IgGb) observed in foals?
“IgG4-7 proteins are present in pre-suckle serum
When does endogenous production of immunoglobulin E (IgE) occur in foals?
“Delayed until six months old
What effect do passively transferred antibodies have on endogenous immunoglobulin production in foals?
“They may have a suppressive effect
What cytokine production is observed in foal peripheral blood mononuclear cells (PBMCs)?
“Active production of TNF-alpha
What immune responses do young foals generate to experimental infection and vaccine challenges?
“Antigen-specific humoral and cell-mediated immune responses
What is the effect of vaccinating mares before foaling?
“Maximizes antigen-specific antibody transfer to the neonate through colostrum
What are the challenges in neonatal vaccination?
“The need for immediate protection early in life with long-term memory
What vaccination strategy has been effective against Rhodococcus equi in foals?
“Oral vaccination at two
What are the implications of early exposure to environmental pathogens for neonatal foals?
“Exposure to pathogens before immune system priming can lead to disease
