Which antibodies elicit first when an antigen is administered for the first time to a human?

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2022

Explanation

Upon the first encounter with an antigen, the immune system initiates a primary response.
IgM is the first antibody class produced and secreted by plasma cells during this initial response.
The appearance of IgM in the blood is a key indicator of a recent or current infection.
It is a large pentameric molecule, which makes it highly effective at clumping pathogens and activating the complement system.

Option A: IgG is the predominant antibody in the secondary immune response, not the primary one.
Option B: IgA is a secretory antibody, primarily providing localized protection at mucosal surfaces like the gut and respiratory tract.
Option D: IgE is primarily involved in type I hypersensitivity (allergic reactions) and defense against parasitic worms.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Primary Immune Response and Immunoglobulin Classes as background academic context rather than a clinical decision trigger.
Understanding the sequence of antibody production is crucial for interpreting serology tests.
The presence of IgM antibodies against a specific pathogen suggests a current or very recent infection.
The presence of IgG antibodies, in the absence of IgM, typically indicates a past infection or immunity from vaccination.

How to Approach the Question

First, identify the key terms in the question: 'antibodies', 'first time', and 'antigen'.
Recognize that 'first time' exposure to an antigen triggers the 'primary immune response'.
Recall the sequence of events in a primary immune response.
Remember the mnemonic 'Me First' for IgM, as it is the first antibody to appear.
Differentiate this from the secondary response, where IgG is the main player ('Grandma's memory' - IgG for long-term memory).
Select the option corresponding to the first antibody produced in the primary response.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) p. 94-96

E6 Medicine Harrison 22e Part 2 p. 683-685

Practise the full RUHS, Jaipur, PB B.Sc Nursing Entrance-2022

Attempt every question from this paper in a timed mock, then review the full solution for each one.