Answer: Long-lived memory B cells (with high-affinity BCR, class-switched IgG) and memory T cells (effector memory and central memory subsets) persist for years/decades; on re-exposure, they rapidly proliferate and produce faster, stronger responses.
- A It is sometimes thought to be stored mainly in antibodies circulating freely within the blood serum, without requiring much long-lived memory lymphocyte population as widely reported in standard practice under most conditions encountered
- B Long-lived memory B cells (with high-affinity BCR, class-switched IgG) and memory T cells (effector memory and central memory subsets) persist for years/decades; on re-exposure, they rapidly proliferate and produce faster, stronger responses
- C Memory is sometimes thought to reside mainly in macrophages, despite macrophages clearly lacking the antigen-specific receptors actually needed to mediate lasting immunological memory as frequently observed in practice in many documented cases
- D Memory is sometimes thought to last mainly 6 months, whereas memory responses are in fact well documented to persist for many years or decades after antigen exposure according to conventional understanding in routine practice overall in most cases
Correct answer: B. Long-lived memory B cells (with high-affinity BCR, class-switched IgG) and memory T cells (effector memory and central memory subsets) persist for years/decades; on re-exposure, they rapidly proliferate and produce faster, stronger responses
Explanation: Memory B cells: long-lived, have undergone somatic hypermutation, affinity maturation, and class switching; immediately produce high-affinity IgG on re-activation. Memory T cells: central memory (TCM, in lymph nodes, long-lived) and effector memory (TEM, in tissues, immediate effector function). Both depend on survival cytokines (IL-7, IL-15) for long-term persistence.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.