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THE IMMUNE SYSTEMChapter 43
What you must know:
• Several elements of an innate immune response• The differences between B and T cells relative
to their activation and actions.• How antigens are recognized by immune
system cells• The differences in humoral and cell-mediated
immunity• Why Helper T cells are central to immune
responses
Types of Immunity
Innate Immunity Adaptive Immunity
• Non-specific• All plantsplants & animalsanimals
• Pathogen-specific• Only in vertebratesvertebrates• Involves B and T cells
Plant Defenses
• Nonspecific responses• Receptors recognize pathogen molecules
and trigger defense responses– Thicken cell wall, produce antimicrobial
compounds, cell death• Localize effects
Pathogens(such as bacteria,fungi, and viruses)
INNATE IMMUNITY(all animals)
• Rapid response
Recognition of traits sharedby broad ranges ofpathogens, using a smallset of receptors
•
Recognition of traits specific to particularpathogens, using a vastarray of receptors
•
• Slower response
Barrier defenses:SkinMucous membranesSecretions
Internal defenses:Phagocytic cellsNatural killer cellsAntimicrobial proteinsInflammatory response
Humoral response:Antibodies defend againstinfection in body fluids.
Cell-mediated response:Cytotoxic cells defendagainst infection in body cells.
ADAPTIVE IMMUNITY(vertebrates only)
Figure 43.2
Barrier Defenses:•Skin•Mucous membranes•LysozymeLysozyme (tears, saliva, mucus)
Inflammatory Response:•Mast cells Mast cells release histaminehistamine•Blood vessels dilate, increase permeability (redness, swelling)•Deliver clotting agents, phagocytic cells•Fever
Phagocytic WBCs:•Neutrophils (engulf)•MacrophageMacrophage (“big eaters”)•Eosinophils (parasites)•Dendritic cells (adaptive response)
Natural Killer Cells:•Virus-infected and cancer cells
Antimicrobial Proteins:•InterferonsInterferons (inhibit viral reproduction)•Complement systemComplement system (~30 proteins, membrane attack complex)
Innate Innate ImmunityImmunity
(non-specific)
Innate Innate ImmunityImmunity
(non-specific)
Phagocytosis
Inflammatory Response
Lymphatic System: involved in adaptive immunity
Adaptive Response
LymphocytesLymphocytes (WBCs): produced by stem cells in bone marrow
•T cellsT cells: mature in thymus– helper T, cytotoxic T
•B cellsB cells: stay and mature in bone marrow
– plasma cells antibodies
• AntigenAntigen: substance that elicits lymphocyte response
• AntibodyAntibody (immunoglobulin – Ig): protein made by B cell that binds to antigens
Major Histocompatibility Complex (MHC)Major Histocompatibility Complex (MHC)
• Proteins displayed on cell surface• Responsible for tissue/organ rejection (“self” vs.
“non-self”)• B and T cells bind to MHC molecule in adaptive
response• Class IClass I: all body cells (except RBCs)• Class IIClass II: displayed by immune cells; “non-self”
Humoral Immune Response(antibodies)
Humoral Immune Response(antibodies)
Cell-Mediated Immune Response(T Cells)
Cell-Mediated Immune Response(T Cells)
Antigen-presenting
cell
Helper T cell
B cell Cytotoxic T cell
Plasma cell
Infected Infected cellcellAntibodiesAntibodies
Identify and destroy
tag for destruction
Immunological Memory• Primary immune response: 1st exposure to antigen• Memory cells:Memory cells:
– Secondary immune response: repeat exposure faster, greater response
AntigenAntigenreceptor
Antibody
Plasma cellsMemory cells
B cells thatdiffer inantigenspecificity
Figure 43.14
• Immunizations/vaccinesImmunizations/vaccines: induce immune memory to nonpathogenic microbe or toxin
• Passive immunityPassive immunity: via antibodies in breast milk• AllergiesAllergies: hypersensitive responses to
harmless antigens• Autoimmune DiseasesAutoimmune Diseases:
– Lupus, rheumatoid arthritis, Type I diabetes, multiple sclerosis
• HIVHIV: infect Helper T cells– AIDS = severely weakened immune system