Which one of the following is the major immunoglobulin in human serum?

ESIC Nursing Officer-7July 2024

Applied Physiology

Easy

Appeared in: ESIC Nursing Officer-7July 2024

Explanation

Immunoglobulin G (IgG) is the most abundant class of immunoglobulins in human serum, constituting about 75-80% of the total.
It is the only immunoglobulin that can cross the placental barrier, providing essential passive immunity to the fetus and newborn from the mother.
IgG is the main antibody in the secondary (memory) immune response and plays a vital role in opsonization, complement fixation, and neutralization of toxins and viruses.

Option A: IgA is the second most abundant immunoglobulin overall, but it is primarily found in mucosal secretions (e.g., saliva, tears, breast milk) rather than being the major component of serum.
Option B: IgD is present in very low concentrations in the serum. Its primary function is to act as an antigen receptor on the surface of B lymphocytes.
Option D: IgE has the lowest concentration of all immunoglobulins in the serum. It is primarily bound to mast cells and basophils and is involved in allergic reactions and defense against parasites.

Visual 1: Diagram: A pie chart illustrating the relative percentages of the five immunoglobulin classes (IgG, IgA, IgM, IgD, IgE) in normal human serum. This would visually emphasize the dominance of IgG.
Visual 2: Illustration: A comparative diagram showing the structures of the five immunoglobulin classes, highlighting the monomeric structure of IgG and the polymeric forms of IgA and IgM.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Immunoglobulin classes and their relative abundance in serum as background academic context rather than a clinical decision trigger.
Nurses should understand that IgG's ability to cross the placenta provides newborns with passive immunity for the first few months of life. This is a critical concept in neonatal care and patient education for expectant mothers.
Abnormal levels of immunoglobulins can indicate disease. For example, low IgG levels (hypogammaglobulinemia) increase susceptibility to infections, while high levels can be seen in chronic infections or autoimmune diseases.
What if? If a baby is born prematurely, the transfer of maternal IgG, which peaks in the third trimester, is incomplete. This places the premature infant at a significantly higher risk for infections, requiring vigilant nursing assessment and protective isolation measures.

How to Approach the Question

First, identify the keywords in the question: 'major immunoglobulin' and 'human serum'. This indicates the question is asking for the most abundant antibody in the blood.
Recall the five classes of immunoglobulins: IgG, IgA, IgM, IgD, and IgE. A helpful mnemonic is 'GAMED'.
Access your knowledge about the relative concentrations of these immunoglobulins in the serum. Remember that while the mnemonic is 'GAMED', their abundance in serum follows the order G > A > M > D > E.
Evaluate the given options based on this knowledge. IgG is known to be the most plentiful, making up about 75-80% of serum immunoglobulins.
Confirm that the other options are less abundant in the serum. IgA is mainly secretory, while IgD and IgE are present in trace amounts.
Select IgG as the correct answer based on its highest concentration in the serum.

Concept Tested & Keywords

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