Immunoglobulin which crosses placenta is?

DHS Staff Nurse - 2018 (Shift-2nd)

Applied Physiology

Easy

Appeared in: DHS Staff Nurse - 2018 (Shift-2nd)

Explanation

IgG is the only class of immunoglobulin that can cross the placental barrier from mother to fetus.
This transfer is an active process, not simple diffusion, and is mediated by the neonatal Fc receptor (FcRn) located on the placental cells.
The primary purpose of this transfer is to provide the fetus and newborn with passive immunity, offering protection against infections during the first few months of life as its own immune system develops.
Maternal IgG levels in the newborn's circulation are highest at birth and gradually decline over 3-6 months.

Option A: IgD is primarily found on the surface of B-lymphocytes, where it functions as an antigen receptor. It is present in very low concentrations in the serum and does not have a mechanism for placental transport.
Option C: IgE is the antibody responsible for immediate hypersensitivity and allergic reactions. It is typically bound to mast cells and basophils in tissues and does not cross the placenta.
Option D: IgM has a large pentameric structure, making it too big to pass through the placental barrier. Its presence in a newborn would indicate an intrauterine infection, as the fetus would have produced it itself.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placental transfer of immunoglobulins as background academic context rather than a clinical decision trigger.
Understanding that only IgG crosses the placenta is crucial for neonatal care, as it explains the newborn's temporary passive immunity and subsequent susceptibility to infections as maternal IgG levels wane.
This concept is fundamental to understanding Hemolytic Disease of the Newborn (HDN), where maternal IgG antibodies against fetal red blood cells (e.g., Rh factor) cross the placenta and cause hemolysis.
The timing of infant vaccinations is scheduled to begin as maternal IgG protection starts to decrease, ensuring the infant can develop its own active immunity.

How to Approach the Question

First, identify the core concept of the question, which is the transfer of antibodies across the placenta.
Recall the different classes of immunoglobulins (GAMED - IgG, IgA, IgM, IgE, IgD) and their primary functions and structures.
Associate IgG with its unique ability for placental transfer, a key fact in immunology. Remember 'G' for 'Goes' across the placenta.
Consider the structure of other immunoglobulins. For example, remember that IgM is a large pentamer ('M' for 'Mega'), making it physically too large to cross.
Eliminate the other options based on their known primary roles: IgE in allergy, IgA in secretions, and IgD as a B-cell receptor.

Concept Tested & Keywords

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