Regarding "Primary immune response", which is the correct statement?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Applied Microbiology & Infection control

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Explanation

The primary immune response occurs upon the first encounter with a specific antigen.
It is characterized by a slow and less potent (sluggish) production of antibodies.
There is a significant lag period of 4-7 days before antibodies are detectable in the serum.
The initial antibody produced is predominantly of the IgM class.

Option A: The predominant antibody in the primary response is IgM. While IgG is produced later and in smaller amounts, a high titer of IgG is the hallmark of the secondary response.
Option B: The main antibody-producing cells in a primary response are plasma cells that differentiate from naive B cells. Memory B cells are generated during this phase but do not actively secrete antibodies; their role is to mount a rapid response upon subsequent antigen exposure.
Option C: A lag period of several days (typically 4-7 days) is a defining feature of the primary immune response. This period is necessary for antigen processing, presentation, and the activation and differentiation of lymphocytes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Characteristics of the primary immune response as background academic context rather than a clinical decision trigger.
Understanding the difference between primary and secondary responses is fundamental to vaccination principles. The first dose of a vaccine induces a primary response, creating immunological memory.
Booster doses are administered to trigger a rapid and robust secondary response, leading to higher antibody levels (mainly IgG) and long-lasting protection.
Patient education is crucial. Nurses must explain why completing a full vaccination series, including boosters, is necessary for achieving durable immunity against diseases like tetanus, measles, and COVID-19.

How to Approach the Question

First, identify the core concept: the question asks for a correct statement about the 'primary immune response'.
Recall the definition of a primary immune response: the body's first-ever encounter with a specific antigen.
Mentally contrast this with the secondary (anamnestic) response, which is faster and stronger.
Evaluate each option against the known characteristics of a primary response:
Option A (Involves IgG): Is IgG the main antibody? No, IgM is the first and predominant one.
Option B (Memory B cells produce antibodies): Do memory cells produce antibodies in the primary phase? No, plasma cells do. Memory cells are for the next time.

Concept Tested & Keywords

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