Prevent entry.
Skin, mucus, chemistry.
Many threats are stopped before immune cells are activated.
Side 63
Immunology
A study of biological defense and self-recognition. Immunology connects detection, signaling, innate response, adaptive specificity, memory and tolerance into a system that must react strongly enough to protect without damaging the host.
detect→signal→respond→remember→regulate
06immune lenses
05cell families
05regulation problems
63Side
Innate immunity responds quickly to recurring danger patterns.
Physical barriers, soluble molecules and immune cells provide immediate defense before highly specific adaptive responses develop.
Detect conserved danger patterns.
Pattern-recognition receptors.
Innate receptors recognize recurring molecular features associated with microbes or damage.
Recruit and activate.
Cytokines + chemokines.
Signals coordinate local inflammation and cell movement.
Destroy or contain.
Phagocytosis, complement, cytotoxicity.
Different innate mechanisms eliminate extracellular and intracellular threats differently.
Activate adaptive immunity.
Antigen presentation.
Dendritic cells and other antigen-presenting cells connect innate sensing to adaptive specificity.
Adaptive immunity expands rare cells that recognize a specific target.
Specificity is generated before exposure; infection or vaccination selects and expands the matching clones.
Recognizes antigen and produces antibody.
Activated B cells can differentiate into antibody-secreting plasma cells and memory cells.
Coordinate immune responses.
Helper T-cell subsets guide B cells, macrophages and other immune cells through cytokines and cell contact.
Kill infected or abnormal cells.
Cytotoxic T cells recognize peptides presented on MHC class I molecules.
Specific clones expand.
Antigen exposure amplifies lymphocytes whose receptors match the target.
Display peptide fragments.
MHC molecules expose intracellular or acquired peptides for T-cell recognition.
Receptor diversity is enormous.
Gene rearrangement generates diverse antigen receptors before exposure.
Antibodies turn recognition into soluble defense.
Antibody structure separates antigen binding from downstream immune effects.
Binding
Variable regions recognize antigen.
Binding specificity depends on molecular complementarity.
Neutralize
Block biological function.
Antibodies can prevent toxins or pathogens from binding host targets.
Opsonize
Mark targets for uptake.
Fc receptors on immune cells recognize antibody-coated targets.
Complement
Recruit a soluble effector cascade.
Some antibody classes efficiently trigger complement activation.
Class switch
Change effector function without changing specificity.
B cells can retain antigen recognition while changing antibody isotype.
T cells recognize antigen only in cellular context.
T-cell receptors read peptide–MHC complexes rather than freely circulating antigen.
| T-cell role | Main recognition context | Core function | Failure risk |
|---|---|---|---|
| CD4 helper | MHC II | Coordinate immune response | Insufficient or misdirected help |
| CD8 cytotoxic | MHC I | Kill infected/abnormal cells | Tissue damage if misdirected |
| Regulatory T cell | Self / inflammatory context | Suppress inappropriate activation | Autoimmunity if regulation fails |
| Memory T cell | Previously encountered antigen | Faster secondary response | Can contribute to chronic inflammation |
Immune memory changes the second encounter.
Memory B and T cells persist after the initial response and can respond faster and more effectively on re-exposure.
Specific clones increase.
Primary exposure builds a larger pool of antigen-experienced cells.
Antibody binding can improve.
Selection in germinal centers enriches B-cell clones with higher-affinity receptors.
Rapid recall capacity.
Memory cells can differentiate quickly on later exposure.
Sustain antibody production.
Some plasma cells persist and maintain circulating antibodies.
Faster cellular response.
Memory subsets differ in tissue location and recall behavior.
Memory is not one thing.
Antibody level, memory-cell abundance and protection can decline at different rates.
Protection requires restraint.
Immune systems must tolerate self and harmless exposure while preserving capacity to respond to real threats.
Central tolerance
Developing lymphocytes that strongly recognize self are removed or redirected.
Peripheral tolerance
Additional controls suppress self-reactive cells that escape development.
Checkpoint
Activation requires more than receptor recognition alone.
Resolution
Inflammation must switch off after the threat is controlled.
Dysregulation
Failure can produce immunodeficiency, autoimmunity, allergy or chronic inflammation.
Janeway’s Immunobiologyimmune-system foundation
Cellular and Molecular ImmunologyAbbas et al. · mechanism-focused immunology
The Immune SystemPeter Parham · integrated overview
How the Immune System WorksLauren Sompayrac · conceptual introduction