Which immunoglobulin can cross the placenta and can provide passive immunity to the newborn?

AIIMS Raipur NO - 2019 (Shift-1)

Applied Physiology

Easy

Appeared in: AIIMS Raipur NO - 2019 (Shift-1)

Explanation

IgG is the only immunoglobulin class capable of crossing the placental barrier.
This transplacental transfer is possible due to its relatively small molecular weight and a specific transport mechanism in the placenta.
This process provides the fetus and newborn with 'natural passive immunity' against pathogens the mother has been exposed to.
Maternal IgG levels in the newborn's circulation are highest at birth and gradually decline over the first few months of life as the infant begins to produce its own antibodies.

Option B: IgE is primarily involved in mediating allergic and hypersensitivity reactions. It does not cross the placenta and is not involved in providing passive immunity to the newborn.
Option C: IgM is a large, pentameric molecule, which makes it physically too big to cross the placental barrier. It is the first antibody produced during a primary immune response.
Option D: IgA is the main immunoglobulin found in bodily secretions. It provides mucosal immunity but is transferred to the newborn through breast milk (colostrum), not across the placenta.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Maternal-fetal immunoglobulin transfer and passive immunity as background academic context rather than a clinical decision trigger.
The transfer of maternal IgG is a cornerstone of neonatal immunity, highlighting the importance of maternal health and vaccination history before and during pregnancy.
The presence of specific IgM antibodies in a newborn's cord blood is a key diagnostic marker for congenital infections like rubella, cytomegalovirus (CMV), or toxoplasmosis.
Nurses play a vital role in educating new mothers about the benefits of breastfeeding, as colostrum is rich in IgA, which provides crucial protection against respiratory and gastrointestinal infections.

How to Approach the Question

First, identify the key concepts in the question: 'immunoglobulin', 'cross the placenta', and 'passive immunity for the newborn'.
This is a factual recall question. Access your knowledge about the five major classes of immunoglobulins (IgG, IgA, IgM, IgE, IgD).
Recall the primary function and unique characteristics of each class, specifically focusing on their ability to cross the placenta.
Remember that IgG is unique in its ability to be transported across the placenta.
Differentiate this from IgA, which is passed through breast milk, and IgM, which is too large to cross.
Select the option that matches the characteristic of placental transfer, which is IgG.

Concept Tested & Keywords

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