📌Definition Table

Term	Definition
Adaptive immunity	A specific immune defence that develops after exposure to a pathogen, involving memory.
Antigen	A foreign molecule that triggers an immune response.
B cells	Lymphocytes that mature in bone marrow and produce antibodies.
T cells	Lymphocytes that mature in the thymus, coordinating and regulating immune responses.
Antibody	A protein secreted by plasma cells that specifically binds to antigens.
Memory cells	Long-lived lymphocytes that remain after infection, providing faster responses upon re-exposure.

📌Introduction

Adaptive immunity provides specific, long-lasting defence against pathogens. Unlike innate immunity, it tailors responses to particular antigens and creates memory for future encounters. It involves B cells, which produce antibodies, and T cells, which regulate and destroy infected cells. Adaptive immunity is slower to develop but highly effective, underpinning vaccination strategies

📌 B Cells and Antibody Production

• B cells recognise antigens via surface receptors (membrane-bound antibodies).
• Once activated (with T helper cell support), they differentiate into:
  • Plasma cells: secrete large amounts of antibodies.
  • Memory B cells: provide long-term immunity.
• Antibodies neutralise toxins, opsonise pathogens, and activate complement.
• Different classes of antibodies (IgG, IgA, IgM) serve specialised roles.
• Antibody diversity arises from gene rearrangements during B cell development.

🧠 Examiner Tip: Don’t confuse plasma cells (short-lived, secrete antibodies) with memory B cells (long-lived, no immediate secretion).

📌 T Cells and Their Roles

• Helper T cells (Th): release cytokines, activate B cells and cytotoxic T cells.
• Cytotoxic T cells (Tc): kill virus-infected and cancer cells by releasing perforins and granzymes.
• Regulatory T cells (Treg): suppress excessive immune responses, preventing autoimmunity.
• Memory T cells: ensure rapid responses on re-exposure.
• T cells require antigen presentation by major histocompatibility complex (MHC) molecules.

🧬 IA Tips & Guidance: Students could model antibody–antigen interactions using lock-and-key analogies, or use ELISA-based classroom kits to demonstrate antibody binding.

📌 Clonal Selection and Expansion

• Each B or T cell has unique antigen receptors generated randomly.
• When a specific antigen binds, that cell is “selected” and undergoes rapid clonal expansion.
• Creates a population of cells with the same specificity.
• This process explains the specificity and adaptability of immune responses.
• Memory cells formed during clonal expansion underpin long-term immunity.

🌐 EE Focus: An EE could examine how clonal selection theory revolutionised immunology, comparing historical and modern models of immune specificity.

📌 Integration with Innate Immunity

• Antigen-presenting cells (APCs) like dendritic cells activate T helper cells.
• Cytokines from innate immune cells influence adaptive responses.
• Adaptive responses enhance innate immunity (antibodies activate complement, opsonisation).
• Both systems are interdependent, not separate.
• Failures in integration (e.g., HIV destroying helper T cells) cripple immunity.

❤️ CAS Link: Students could create peer-to-peer teaching sessions using role-play to model immune cell interactions (e.g., APCs, B cells, T cells as characters).

📌 Immune Memory and Specificity

• Primary response: slower, with lower antibody levels.
• Secondary response: faster, stronger, due to memory B and T cells.
• This principle underlies vaccination strategies.
• Specificity ensures pathogens are targeted precisely, minimising collateral damage.
• Autoimmune diseases occur when specificity fails, and self-antigens are targeted.

🔍 TOK Perspective: Adaptive immunity is often described as the body “learning.” But is this metaphor misleading? Memory in biology is chemical and cellular, not conscious. TOK question: How far can we extend human metaphors like “memory” and “recognition” to scientific processes?

📝 Paper 2: Questions may involve comparing B and T cell functions, explaining clonal selection, or describing primary vs secondary immune responses. Data questions often show antibody concentration graphs over time. Use precise terminology (plasma cells, memory cells, cytokines).