Clinical immunology chapter 2: The Immune System of the Young Horse Flashcards
(40 cards)
What is the paradox of neonatal vaccination?
The paradox involves the need for immediate protection early in life with long-term memory, challenges of the neonatal immune system, and concerns about maternal antibody interference.
How does the foetal immune system develop, particularly regarding lymphoid populations and immunoglobulin diversity?
Lymphoid populations start developing in the thymus around 80 days of gestation, and primary germinal centers in the spleen and mesenteric lymph nodes appear around day 200. B cell differentiation and Ig isotype switching become active around mid-gestation (around day 100). The foetal immune system shows a wide repertoire of Ig antigen specificity, rapidly increasing between day 100 gestation and birth.
How does passive transfer of immunity occur in foals, and what is the role of colostrum?
The epitheliochorial placenta prevents the transfer of maternal antibodies to the foetus in utero. Foals are born with non-protective amounts of endogenous serum IgM and IgG due to this barrier. Colostrum, containing innate immune proteins, cellular components, and antibodies, plays a crucial role in providing passive transfer of antibodies to the foal.
What are the components of colostrum that contribute to passive immunity in foals?
Colostrum contains complement components (C3), cytokines (TNF-alpha, IL-6), lysozyme, ferritin, antibodies, and cellular components such as maternal lymphocytes, neutrophils, macrophages, and epithelial cells.
How does the innate immune system of neonatal foals change over time, and what factors contribute to its activation?
Neonatal foals have intrinsic phagocytic and oxidative burst activities at birth. Phagocytes, particularly neutrophils, express higher levels of integrin molecule CD18 during their initial three weeks of life. Opsonization with colostrum-derived IgG is crucial for phagocytosis and bacterial killing.
When does endogenous immunoglobulin production begin in foals, and what is the significance of IgG4-7?
Endogenous immunoglobulin production begins during foetal life, with appreciable levels of serum IgM and IgG attained by 2–3 months of life. IgG4-7 is the most abundant IgG isotype in adult serum and colostrum, and its delayed production is reported in foals.
How does the adaptive immune system of foals develop, and when does endogenous immunoglobulin production start?
The adaptive immune system of foals is naïve at birth. Exposure to pathogens induces expansion of lymphocyte populations. Circulating B and T lymphocyte populations expand linearly over the first five months of life, plateauing at numbers greater than that of adult horses for a few months. Endogenous immunoglobulin production begins during foetal life.
What is the effect of passively transferred antibodies on endogenous immunoglobulin production in foals?
Some studies suggest that passively transferred antibodies may have a suppressive effect on the foal’s endogenous immunoglobulin production. However, foals are observed to generate antigen-specific immune responses in early life, even with circulating colostrum-derived antibodies.
How do foal peripheral blood mononuclear cells (PBMCs) demonstrate immunocompetence in the first month of life?
Foal PBMCs exhibit active cytokine production, including TNF-alpha, IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p35, IL-15, and IL-18. The proportion of IFN-gamma and IL-10 producing-cells increases over the first six weeks of life, with IFN-gamma expression reaching adult levels by three months old.
How do neonatal foals respond to experimental infection and vaccine challenges?
Experimental infection and vaccine challenges reveal the ability of young foals to generate antigen-specific humoral and cell-mediated immune responses. Foals are immunocompetent but may require a specific immunogenic context to generate the desired immune response.
Describe the immune development milestones during the foetal period, focusing on germinal centers and B cell differentiation.
Germinal centers in spleen and mesenteric lymph nodes develop around day 200 of gestation. Mid-gestation sees B cell differentiation, mature B cells, and Ig isotype switching in the liver, bone marrow, and spleen, with B cell transcripts expressed by day 100.
What are the components of colostrum that contribute to innate immunity, and how do they benefit foals?
Colostrum contains complement components (C3), cytokines (TNF-alpha, IL-6), lysozyme, ferritin, and antibodies. It provides essential immune proteins and cells, aiding in the passive transfer of antibodies, thereby enhancing the innate immunity of foals.
How does the neonatal innate immune system change regarding opsonization and chemotactic factors after colostrum ingestion?
Before colostrum ingestion, foal serum has fewer chemotactic and opsonic factors. After colostrum ingestion, opsonic capacity significantly increases, reaching levels comparable to adults by 3–4 weeks of life. The age-dependent increase in complement levels is observed, and administration of adult plasma enhances opsonic ability.
When does the bronchus-associated lymphoid tissue (BALT) develop in foals, and how does it contribute to immune development?
Foals lack organized lymphoid tissue in the lungs at birth, but BALT is observed by 12 weeks old. The expansion of lymphocyte populations in bronchoalveolar lavage fluid occurs gradually in the first three months, contributing to respiratory immune defense.
What is the significance of IgG4-7 in foals, and when is it expressed in response to Rhodococcus equi challenge?
IgG4-7 is the most abundant IgG isotype in adult serum and colostrum. Foals express IgG4-7 at earlier time points, with mRNA expression in neonatal spleen and peripheral blood. Serum IgG4-7 is produced in foals younger than one month when challenged with Rhodococcus equi.
How does the foetal immune system respond to antigen exposure, and what is the role of antigen-specific lymphocyte populations?
Antigen exposure induces a massive expansion of antigen-specific lymphocyte populations in early life. This leads to a 2–3 times increase in circulating lymphocytes, an increase in secondary lymphoid tissue mass, and the establishment of primed cells, contributing to immune memory.
Explain the temporal dynamics of circulating B and T lymphocyte populations in neonatal foals and their correlation with exposure to environmental antigens.
Circulating B and T lymphocyte populations in foals expand linearly over the first five months of life, plateauing at numbers greater than adult horses for a few months. The expansion correlates with exposure to environmental antigens, leading to lymphocyte activation and proliferation.
How does the thymus, spleen, and systemic lymph nodes contribute to the immune system in foals, and what structures develop postnatally?
Thymus, spleen, and some systemic lymph nodes develop their structure during foetal life. Bronchus-associated lymphoid tissue (BALT) appears postnatally by 12 weeks old. Expansion of lymphocyte populations in bronchoalveolar lavage fluid occurs gradually in the first three months.
What is the role of IgE in neonatal foals, and when does endogenous IgE production become robust?
Most IgE bound to neonatal basophils is of maternal origin. Endogenous production of IgE appears delayed until six months old, with robust serum IgE levels by 9–11 months, despite the decay of colostrum-derived IgE by four months.
How do foals demonstrate immunocompetence in response to experimental infection and vaccine challenges, and is the memory response characterized?
Foals show the ability to generate antigen-specific humoral and cell-mediated immune responses to experimental infection and vaccine challenges. While foals are immunocompetent, the memory response has not been fully characterized yet, and further research is needed to understand the nuances.
Describe the time frame for colostrum preparation and its significance in providing immunoglobulins to the equine neonate.
Colostrum preparation begins a couple of weeks pre-foaling and is active in the first 12 hours post-foaling. This timeframe is critical for efficient absorption of immunoglobulins, with absorption peaking around eight hours post-foaling and lasting, with limitations, up to 24 hours.
What are the primary immunoglobulin isotypes found in equine colostrum, and how do they contribute to humoral protection?
Equine colostrum is rich primarily in IgG4/7, with small amounts of other IgG isotypes, IgM, IgA, and IgE. Colostrum-derived IgG, particularly IgG4/7, is essential for humoral protection, providing vital neutralization and opsonization properties.
Explain the concept of Failure of Passive Transfer (FPT) in foals and its consequences.
FPT occurs if the foal doesn’t suckle adequate colostrum or if it can’t efficiently absorb immunoglobulins. Foals with FPT remain hypogammaglobulinemic, leading to susceptibility to infections. It is defined by a serum IgG concentration less than 800 mg/dL by 24 hours old, with partial FPT between 400 and 800 mg/dL.
What factors contribute to the occurrence of Failure of Passive Transfer (FPT) in foals, and what is the estimated incidence?
FPT may result from inadequate suckling, inefficient absorption, or colostrum lacking sufficient immunoglobulins. The estimated incidence of FPT is between 10–18% of foals, with factors such as older dams, specific gravity less than 1.06, and environmental conditions influencing prevalence.
