THE IMMUNE SYSTEM

Chapter 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 plants & animals

• Pathogen-specific

• Only in vertebrates

• Involves B and T cells

Barrier Defenses: •Skin

•Mucous membranes

•Lysozyme (tears,

saliva, mucus)

Inflammatory Response: • Mast cells release histamine

• Blood vessels dilate, increase

permeability (redness,

swelling)

• Deliver clotting agents,

phagocytic cells

• Fever

Phagocytic WBCs: •Neutrophils (engulf)

•Macrophage (“big eaters”)

•Eosinophils (parasites)

•Dendritic cells (adaptive

response)

Natural Killer

Cells: •Virus-infected and

cancer cells

Proteins: • Interferons (inhibit viral

reproduction)

• Complement system (~30 proteins,

membrane attack complex)

Innate

Immunity (non-specific)

Phagocytosis

Lymphatic System: involved in adaptive immunity

Inflammatory Response

Adaptive Response

• Lymphocytes (WBCs):

produced by stem cells in

bone marrow

– T cells: mature in thymus

• helper T, cytotoxic T

– B cells: stay and mature

in bone marrow

• plasma cells antibodies

• Antigen: substance that elicits lymphocyte

response

• Antibody (immunoglobulin – Ig): protein made by

B cell that binds to antigens

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 I: all body cells (except RBCs)

• Class II: displayed by immune cells; “non-self”

Humoral Immune Response

(antibodies)

Cell-Mediated Immune

Response

(T Cells)

Antigen-

presenting

cell

Helper T

cell B cell Cytotoxic T

cell

Plasma

cell

Infected

cell Antibodies

Identify and

destroy

tag for

destruction

Immunological Memory

• Primary immune response: 1st exposure to antigen

• Memory cells:

– Secondary immune response: repeat exposure

faster, greater response

Antigen Antigen receptor

Antibody

Plasma cells Memory cells

B cells that differ in antigen specificity

Figure 43.14

• Immunizations/vaccines: induce immune

memory to nonpathogenic microbe or toxin

• Passive immunity: via antibodies in breast milk

• Allergies: hypersensitive responses to

harmless antigens

• HIV: infect Helper T cells

– AIDS = severely weakened immune system

• Immunological Diseases:

– Lupus, rheumatoid arthritis, Type I diabetes,

multiple sclerosis