ryan- fetal and neonatal immunity

How does immune system development differ in poultry versus mammals?

Poultry can be vaccinated in ovo around days 18–19 to stimulate acquired immunity early. Mammalian immune development occurs gradually throughout gestation

What are the gestation lengths and early developmental milestones in cattle and horses?

Cattle: 281 days; enter uterus at 3.5 days and implant at 30–35 days. Horses: 337 days; enter uterus at 5 days and implant at 35–40 days

How is the fetal bovine immune system developed?

Different organs/factors of the immune system are developed over many days of gestation

Why can fetal calves infected with BVDV between days 30–125 become persistently infected?

Their immune systems are not fully developed, so they may recognize the virus as self rather than non-self

What are the three placental membrane types, their species, and number of tissue layers?

Epitheliochorial: cows, pigs, horses (4 layers). Endotheliochorial: dogs, cats (3 layers). Hemochorial: humans, rodents (2 layers).

Are mammalian neonates born immunocompetent?

Most are born immunocompetent (able to mount an immune response) but immunologically naive, meaning they have not encountered specific pathogens

What is the major exception to mammals being born immunocompetent?

Opossums are not born with a fully functioning immune system, it develops around 18 days after birth

What immune defenses does a foal have at birth? What do they lack?

Innate immunity, including digestive enzymes, neutrophils, macrophages, and dendritic cells. Foals lack helper and cytotoxic T cells at birth

How long does it take to develop a maximal acquired immune response?

Approximately 7–14 days (or like 10-14)

What does a neonate need from its mother to survive until its acquired immunity develops?

Colostrum, which provides maternal antibodies, immune cells, cytokines, and nutrients for protection

What does colostrum contain?

Fats, proteins, carbohydrates, antibodies, lymphocytes, cytokine proteins, and other immune cells

What is FcRn and what is its role in passive immunity?

FcRn (neonatal Fc receptor) binds the Fc portion of antibodies and transports maternal antibodies across GI mucosal cells into the neonate's body

How does FcRn transport antibodies across intestinal cells?

It binds the antibody's Fc portion, pulls it into an endosome for protection from degradation, transports it across the cell, and releases it due to pH differences

What is gut closure and when does it occur?

Gut closure is when the neonate loses the ability to absorb maternal antibodies through the GI tract and it occurs around 24 hours after birth

How can passive antibody transfer be measured in foals?

Using a foal IgG SNAP test

What happens if a foal does not receive adequate colostrum?

It may become very sick due to inadequate passive immune protection

What are the five protective mechanisms of antibodies?

Agglutination, opsonization, neutralization, antibody-dependent cell-mediated cytotoxicity (ADCC), and complement activation

How does agglutination protect the neonate?

Antibodies clump antigens together, reducing the number of infectious units

How does opsonization protect the neonate?

Antibodies coat antigens to enhance phagocytosis

How does neutralization protect the neonate?

Antibodies block bacteria and viruses from adhering to mucosal surfaces

What is antibody-dependent cell-mediated cytotoxicity (ADCC)?

Antibodies attach to target cells and help macrophages, eosinophils, and NK cells destroy them

How does antibody activation of complement protect the neonate?

It causes inflammation and cell lysis

How does colostrum provide local immunity?

Antibodies and immune cells in the GI tract help block pathogens from entering the body or exerting their effects

How do immune cells and cytokines in colostrum benefit the neonate?

Immune cells provide some innate defense, while cytokines help direct immune responses

How do maternal antibodies affect vaccination?

They can bind vaccine antigens and cause them to be cleared before they stimulate the neonate's own immune response

Which vaccine type is especially susceptible to maternal antibody interference?

Killed vaccines

Why do puppies and kittens receive multiple vaccine boosters?

To account for varying maternal antibody levels and reduce the chance of maternal antibody interference

Why do maternal antibody levels decline over time?

They are gradually used up or broken down because they are older proteins

What happens to neonatal antibody levels as maternal antibodies decline?

The neonate's own antibody levels increase through exposure to pathogens and development of its acquired immune response

What is the window of susceptibility?

The period when maternal antibodies have declined but the neonate has not yet produced enough of its own antibodies to provide protection

What is the goal of neonatal vaccination timing?

Minimize the window of susceptibility by vaccinating as maternal antibodies decline, while avoiding maternal antibody interference