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