11.1 Fetal and Neonatal Immunity

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Questions and Answers

What is the primary reason newborn mammals rely on passive immune transfer from their mothers?

Their adaptive immune mechanisms are fully developed.

They produce antibodies immediately after birth.

They are born into a sterile environment.

They move into an environment rich in pathogens. (correct)

Which of the following statements accurately describes the timeline for fetal immune system development in calves?

Calves can respond to rotavirus only after birth.

B cells appear before the spleen and lymph nodes develop.

Antibodies are present throughout fetal life.

Calves can respond to parainfluenza 3 virus by 120 days of gestation. (correct)

What initiates the development of the immune system in animals during fetal life?

Formation of the secondary lymphoid organs.

Development of the thymus. (correct)

Activation of the innate immune response.

Production of antibodies in the fetus.

What is a significant difference in maternal transfer of immunity across species?

The timing and efficiency of maternal antibody transfer differ due to physiological variations. Signup and view all the answers

Why is the rationale for neonatal vaccination important?

Neonates are susceptible to infections due to incomplete immune maturity. Signup and view all the answers

What is the significance of the timing of viral infection in pregnant cows regarding BVDV?

Early infection leads to calves tolerant to BVDV. Signup and view all the answers

Which immune response is primarily developed in newborn mammals at birth?

Adaptive immune response skewed toward Th2 cells. Signup and view all the answers

At what age do newborn piglets reach adult levels of C3 complement component?

14 days of age. Signup and view all the answers

What role do cytopathic BVDV infections play in relation to pregnancy outcomes?

They may cause abortion, resorption, or malformations depending on timing. Signup and view all the answers

What is a characteristic of innate immune responses in newborn mammals?

They involve high levels of antimicrobial molecules immediately after birth. Signup and view all the answers

How does the macrophage function in newborn mammals differ from that in adults?

They show delayed efficiency in killing bacteria until 7-10 days. Signup and view all the answers

What generally occurs to innate immune response factors in newborns over time?

They gradually decline in concentration by 21 days. Signup and view all the answers

What is a significant observation regarding lymphocyte counts in dog puppies compared to adult dogs?

Puppies have a higher lymphocyte count than adult dogs. Signup and view all the answers

What type of placenta allows for the transfer of maternal IgG antibodies to the fetus?

Hemochorial placenta Signup and view all the answers

What is the primary advantage of colostrum for newborn mammals?

It contains high concentrations of maternal antibodies. Signup and view all the answers

What is the duration of intestinal permeability for absorbing colostrum in newborns?

It is highest immediately after birth. Signup and view all the answers

What can lead to failure of passive transfer in newborn animals?

Poor maternal care. Signup and view all the answers

How are maternal antibodies related to vaccinations in neonates?

They can interfere with the vaccine's effectiveness. Signup and view all the answers

What characteristic is indicative of good quality colostrum?

Specific gravity between 1.060 to 1.085. Signup and view all the answers

Which factor does NOT contribute to ingestion failure in newborn animals?

Poor maternal quality of the colostrum. Signup and view all the answers

At what time post-birth is the measurement for failure of passive transfer usually conducted?

18-24 hours after birth. Signup and view all the answers

What is a key cytokine found in bovine colostrum?

IL-1β Signup and view all the answers

What role do trypsin inhibitors in colostrum play for the newborn?

Reduce protease activity. Signup and view all the answers

What is the primary reason the immune system in newborn mammals is not fully functional at birth?

The adaptive immune mechanisms are not fully developed. Signup and view all the answers

Which immune-related organ develops first during fetal life in animals?

Thymus Signup and view all the answers

What role does colostrum play in the immune system of newborn mammals?

It provides immediate passive immunity. Signup and view all the answers

At what gestation period can fetal calves begin to respond to rotavirus?

73 days Signup and view all the answers

What is the main consequence of the immature adaptive immune response in newborn mammals?

Increased reliance on maternal immunity. Signup and view all the answers

What is the result of pregnant cows infected with non-cytopathic BVDV early in conception?

They give birth to calves that are tolerant to BVDV. Signup and view all the answers

What type of immune response do most newborn mammals primarily mount?

Responses skewed towards Th2 cells. Signup and view all the answers

When do newborn piglets reach adult levels of the C3 complement component?

By 14 days of age. Signup and view all the answers

What happens to the levels of antimicrobial molecules in newborns over time?

They gradually decline by 21 days. Signup and view all the answers

What is a key difference in the phagocytic capability of macrophages in newborn mammals compared to adults?

Newborn macrophages are less efficient at phagocytosis. Signup and view all the answers

Between what days of conception can infection with cytopathic BVDV cause malformations in calves?

From 100 to 150 days. Signup and view all the answers

What is a characteristic of the immune system development in fetuses during intrauterine infections?

It can result in severe effects from seemingly mild infections. Signup and view all the answers

What effect does the timing of viral infection have on the pregnancy outcomes in cows?

Timing determines the tolerance or malformation of the offspring. Signup and view all the answers

What primarily causes failure of passive transfer due to insufficient colostrum quality?

Insufficient or poor-quality colostrum produced by the mother Signup and view all the answers

What is the main consequence of maternal antibodies in neonates concerning vaccination?

They can bind vaccine antigens and prevent an immune response. Signup and view all the answers

When is the intestinal permeability for absorbing colostrum in newborn mammals at its highest?

Immediately after birth Signup and view all the answers

What is the primary cause of ingestion failure during colostrum consumption in newborns?

Multiple births leading to insufficient intake per offspring Signup and view all the answers

In bovine colostrum, what percentage of IgA is produced locally within the udder?

10% Signup and view all the answers

Which cytokine is notably present in bovine colostrum?

IL-1β Signup and view all the answers

What happens to the absorption of immunoglobulin classes after about 24 hours post-birth?

Absorption of immunoglobulin classes drops to a very low level. Signup and view all the answers

What impact does premature lactation have on colostrum quality?

Reduces both amount and quality of colostrum. Signup and view all the answers

What is the main factor contributing to absorption failure in newborns despite adequate colostrum intake?

Physical problems in the newborn preventing absorption Signup and view all the answers

What is the main function of innate immune mechanisms in newborn mammals at birth?

To provide immediate protection against pathogens Signup and view all the answers

At what stage of fetal development do B cells begin to appear in animals?

After the spleen and lymph nodes have developed Signup and view all the answers

Which factor is most critical for neonatal immunity right after birth?

Maternal transfer of antibodies through colostrum Signup and view all the answers

What is one reason maternal transfer of immunity varies among different species?

Varying structure types of the placenta Signup and view all the answers

Which of the following best describes the immune response of newborn mammals?

It depends heavily on innate immune mechanisms with some adaptive features Signup and view all the answers

What is the impact of maternal infections during pregnancy on the fetus?

They can lead to severe consequences depending on the timing. Signup and view all the answers

Which type of BVDV infection during the first 100 days of pregnancy leads to the most severe outcomes?

Cytopathic BVDV Signup and view all the answers

What is a characteristic feature of the immune response in newborn mammals?

Their initial adaptive responses are skewed toward Th2 cells. Signup and view all the answers

Which statement accurately describes the innate immune capabilities of newborn mammals?

Newborns have high concentrations of certain serum proteins at birth. Signup and view all the answers

What factor is primarily responsible for the slow development of neonatal Th1 cells?

Delayed development of IL-12-producing dendritic cells. Signup and view all the answers

Which component reaches adult levels in newborn piglets by 14 days of age?

C3 complement component Signup and view all the answers

How does maternal infection with non-cytopathic BVDV affect the offspring if contracted early in pregnancy?

It results in immune tolerance to BVDV in the calves. Signup and view all the answers

What happens to serum amyloid A (SAA) levels in newborn mammals over time?

They decline gradually by 21 days. Signup and view all the answers

What is the primary composition of bovine colostrum derived from the bloodstream?

IgG, IgM, and IgA Signup and view all the answers

When does intestinal permeability for absorbing colostrum reach its peak in newborn mammals?

Immediately after birth Signup and view all the answers

What problem may arise from a mother producing inferior quality colostrum?

Inability to provide passive immunity Signup and view all the answers

Which factor contributes to failure of passive transfer through ingestion failure?

Weak suckling drive in the newborn Signup and view all the answers

What significantly affects the timing of neonatal vaccination?

Presence of maternal antibodies Signup and view all the answers

What is a consequence of ingestion failure in newborns related to multiple births?

Inadequate intake of colostrum for all Signup and view all the answers

What is the result of low protease activity in the digestive tract of newborn mammals?

Retention of colostral proteins intact Signup and view all the answers

What role do trypsin inhibitors in colostrum play for newborn mammals?

Reduce protease activity Signup and view all the answers

How does timing affect the absorption of immunoglobulin classes in newborns?

Highest immedately and drops significantly after 24 hours Signup and view all the answers

What is a primary characteristic of good quality colostrum as measured by specific gravity?

Between 1.060 and 1.085 Signup and view all the answers

Study Notes

Fetal and Neonatal Immunity

The immune development of animals occurs during the fetal stage.
Newborns rely on passive immune transfer from the mother, primarily through colostrum.
Innate immune mechanisms are functional at birth, but adaptive mechanisms are not fully functional in certain species.
Animals move from a sterile environment to one with many pathogens and must control infections after birth.
Specific immune development timelines and responses vary widely between species (e.g., calves, puppies).

Objectives

Describe fetal development of immune competence in different animal species.
Describe the immune response of newborn mammals, highlighting innate and adaptive responses.
Explain species differences in maternal transfer of immunity and the underlying causes.
Explain the rationale for neonatal vaccination, including the impact of maternal antibodies.

Development of the Immune System

The thymus develops first among other organs.
Secondary lymphoid organs develop later.
B cells appear after the spleen and lymph nodes develop.
Antibodies are often not detected until late fetal life (if at all).

Calf

The cow gestation period is 280 days.
Fetal calves respond to rotavirus at 73 days, parvovirus at 93 days, and parainfluenza 3 virus at 120 days.

Puppy

The bitch gestation period is about 60 days.
The thymus differentiates between days 23 and 33.
Thymic seeding with T cells is quite late.

The Immune System and Intrauterine Infection

Mild or unapparent infections in the mother can be severe or lethal in the fetus, depending on fetal immune development.
The fetus's response to infection is determined by its immunological development.

Effects of Viral Infection Timing (BVDV)

Pregnant cows infected with noncytopathic BVDV early in conception (up to 120 days) will give birth to calves tolerant to BVDV.
Infection of pregnant cows with cytopathic BVDV within the first 100 days of conception causes abortion, resorption, or mummification of the fetus.
Malformations may occur in calves if the mother is infected with cytopathic BVDV between days 100–150 of gestation.
Calves from mothers infected with cytopathic BVDV after 150 days of gestation might be born normal.

Immune Response of Newborn Mammals

Young mammals are capable of mounting both innate and adaptive immune responses at birth.
Adaptive responses are primary responses, influenced by maternal antibodies.
Innate responses are critical in newborns, particularly for immediate defense.

Innate Immunity

Newborns produce antimicrobial molecules (e.g., lectins, pentraxins, collectins, defensins, lactoferrin, lysozyme).
Serum amyloid A (SAA), lipopolysaccharide-binding protein, haptoglobin, and α1-acid glycoprotein are present in high concentrations immediately after birth but gradually decline by 21 days.
Newborn mammals have deficiencies in some complement components, resulting in poor opsonic activity; the deficiency varies depending on the species and specific component.
C3 in newborn piglets reaches adult levels by 14 days.

Macrophages and NK cells in newborns

Macrophages phagocytose bacteria like Staphylococcus aureus, but are less efficient at killing until after 7–10 days in some species.
Newborn calves have fewer NK cells that respond more strongly to IL-2 or IL-15 and are more cytotoxic compared to adult animals. Cytotoxicity is a key aspect of innate immunity.

Adaptive Immunity

Most newborn mammals have adaptive immune responses skewed towards Th2 rather than Th1 cells.
This is likely due to the delayed development of IL-12-producing DC1 cells in the presence of active DC2 cells that produce IL-4 and IL-13 (which can influence Th2 development.)
Neonatal Th1 cells develop slowly.

Other observations on Dogs and Cats

Dog puppies have a higher lymphocyte count than adult dogs in the first three months, primarily due to more CD21+ B cells than CD8+ T cells (similar to kittens).
Thymic involution begins around 6 months of age in both dogs and cats, a crucial aspect of immune system maturation.

Transfer of Immunity from Mother to Offspring

Transfer of maternal antibodies to the fetus depends on the structure of the placenta.
A hemotrophic placenta (primates) allows the transfer of maternal IgG but not IgM, IgA, or IgE. This is a key structural difference affecting antibody transfer.

Colostrum

Colostrum is the accumulation of immune components in the mammary gland in the last few weeks of gestation and is critical for passive immunity.
Animals that can't transfer antibodies through the placenta rely entirely on those received through the colostrum.
Colostrum is rich in immune components and various cytokines (e.g., IL-1β, IL-6, TNF-α, IFN-γ); these cytokine levels vary in different species.
Immunoglobulin levels in colostrum vary considerably across different species (see Table 21-1). The table shows a wide range of IgG levels across various species.

Absorption of Colostrum

Newborns ingest colostrum (2–6 L) without digesting it efficiently, thanks to reduced protease activity.
Low protease activity in newborns facilitates absorption, crucial for passive immune transfer.
Colostrum's trypsin inhibitors reduce the protease's activity, allowing colostrum proteins to reach the small intestine intact.
Intestinal permeability is highest immediately after birth and declines over time, impacting the duration of antibody absorption and subsequent immunity.

Failure of Passive Transfer

Failure of passive transfer occurs when a newborn cannot ingest the appropriate amount of colostrum, which can impact long-term immunity.
Three major reasons for failure include: production failure (insufficient/poor-quality colostrum), ingestion failure (inadequate consumption), and absorption failure (difficulty absorbing antibodies).

Production Failure

Premature births may lead to insufficient colostrum accumulation.
Premature lactation or excessive pre-birth dripping reduces colostrum amount and quality.
Good-quality colostrum has a specific gravity of 1.060–1.085 (equivalent to an IgG concentration of 3000–8500 mg/dL).
Colostrum with a concentration below 3000 mg/dL is considered poor quality and may not provide adequate protection for the newborn.

Ingestion Failure

Multiple births may result in less colostrum per offspring.
Poor mothering is a significant issue for newborns, impacting their ability to obtain crucial colostral antibodies.
Physical problems (damaged teats), and newborn weakness, a poor suckling drive, or jaw defects can hinder colostrum intake.

Diagnosis of Failure of Passive Transfer

Tests for diagnosing failure of passive transfer, such as glutaraldehyde coagulation (sensitivity 100%, specificity 59%), latex agglutination (sensitivity 72%, specificity 79%), snap test (sensitivity 90%, specificity 79%), turbidimetric immunoassay (sensitivity 81%, specificity 86%), and infrared spectroscopy (sensitivity 93%, specificity 97%), are typically completed after 18–24 hours since most antibody absorption has occurred.

Vaccination of Neonates

Maternal antibodies can interfere with neonatal vaccinations.
Maternal antibodies bind vaccine antigens and prevent immune response generation.
Antibody-antigen complexes formed this way are cleared by cells possessing Fc receptors (e.g., erythrocytes).
Maternal antibodies can mask antigenic epitopes, preventing B cell responses.
Vaccinate neonates after the level of passively acquired maternal antibodies has decreased, to ensure effective activation of the animal's own adaptive immune system.

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