Chapter summary
Immune recognition and memory, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Innate, adaptive, active and passive
Which distinction describes specificity, and which describes the source of protection?
Key idea and reminders
Innate/adaptive describes the response system; active/passive describes whether the recipient makes the protective response or receives antibodies.
- Innate: rapid recognition of broad patterns.
- Adaptive: antigen specificity and memory.
- Active makes a response; passive receives antibodies.
Keep in mind: Transferred antibodies can act immediately; passive refers to their external source.
02
Coordinate an adaptive response
How does a T cell recognise infection inside another cell?
Key idea and reminders
Antigen presentation links cellular evidence of infection to specific T-cell activation and coordinated responses.
- APCs process and present antigen fragments.
- Helper T cells coordinate responses.
- Cytotoxic T cells can eliminate infected cells.
Keep in mind: Plasma cells are differentiated B cells; T cells have coordinating or cell-killing roles.
03
Clonal selection and immune memory
Why is a second response usually faster for the same antigen?
Key idea and reminders
Antigen selects matching pre-existing lymphocyte receptors; expansion and memory change the speed and scale of later responses.
- Selection chooses matching cells.
- Expansion increases their numbers.
- Memory improves response to the same antigen.
Keep in mind: Memory is specific to previously encountered antigenic features, with possible cross-reactivity rather than universal recognition.
04
IgG: bind specifically, recruit help
Why does an antibody need both variable and constant regions?
Key idea and reminders
Variable regions bind an antigenic feature; constant regions recruit other immune components, linking recognition to clearance.
- IgG: two heavy and two light chains.
- Variable regions form antigen-binding sites.
- Fc/constant region supports effector interactions.
Keep in mind: A typical IgG has two equivalent sites with the same specificity.
05
Recombination, hypermutation and class switching
Which process changes binding specificity, and which changes the kind of help recruited?
Key idea and reminders
V(D)J assembly builds binding-site diversity; hypermutation and selection refine affinity; class switching changes the heavy-chain constant region.
- Heavy chain: V-D-J; light chain: V-J.
- Hypermutation plus selection can improve affinity.
- Class switching changes constant-region function, not the selected variable region.
Keep in mind: It changes the heavy-chain constant region; variable-region changes belong to other diversification processes.