Immune System

• Innate immunity is present before any exposure to pathogens and is effective from the time of birth

• It involves nonspecific responses to pathogens• Innate immunity consists of external barriers plus

internal cellular and chemical defenses• Key internal defenses are macrophages and other

phagocytic cells

• Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances

• It involves a very specific response to pathogens• Recognition is by white blood cells called lymphocytes• Some lymphocytes produce antibodies; others destroy

infected cells, cancer cells, or foreign tissue

LE 43-2

Invadingmicrobes

(pathogens)

External defenses

SkinMucous membranesSecretions

INNATE IMMUNITYRapid responses to a

broad range of microbes

ACQUIRED IMMUNITYSlower responses to

specific microbes

Internal defenses

Phagocytic cells

Inflammatory response

Humoral response(antibodies)Antimicrobial proteins

Natural killer cells Cell-mediated response(cytotoxiclymphocytes)

LE 43-4

PseudopodiaMicrobes

MACROPHAGE

Lysosomecontainingenzymes

Vacuole

Natural Killer Cells

• Natural killer (NK), also known as Cytotoxic T Cells, cells attack virus-infected body cells and cancer cells

• They trigger apoptosis in the cells they attack

LE 43-14_3

First exposure to antigen

Antigens engulfed anddisplayed by dendritic cells

Activate

Humoral immune response Cell-mediated immune response

HelperT cell

Active andmemoryhelperT cells

Gives rise to

Antigens displayedby infected cells

Activate

CytotoxicT cell

Memorycytotoxic

T cells

Gives rise to

Secretedcytokinesactivate

Activecytotoxic

T cells

Defend against infected cells, cancercells, and transplanted tissues

Activate

Gives rise to

Secrete antibodies that defend againstpathogens and toxins in extracellular fluid

Plasmacells

MemoryB cells

B cells

Intact antigens