Chapter 24- The Immune System• Active immunity• Allergen• Allergies• Anaphylactic shock• Antibody• Antigen• Antigen receptors• Antigen-binding site• Antigenic determinants• Antigen-presenting cells• Antihistamine• Autoimmune diseases• B cells• Cell-mediated immunity• Clonal selection• Complement proteins• Cytotoxic T cells• Helper T cells• Histamine• Humoral immunity• Immune system• Immunity• Immunodeficiency diseases

• Inflammatory response• Interferons• Lymph• Lymphatic system• Lymphocytes• Macrophages• Major histocompatibility complex• Mast cells• Memory cells• Monoclonal antibodies• Monocytes• Natural killer cells• Neutrophils• Nonself molecules• Passive immunity• Perforin• Plasma cells• Primary immune response• Secondary immune response• Self protein• T cells• Vaccination• Vaccine

Immune system• Protects the body by recognizing and

attacking specific kinds of pathogens and cancer cells

• There are both nonspecific and specific responses against infection

1st line of defense is nonspecificNonspecific = (can’t distinguish a certain pathogen)• Intact skin- barrier that pathogens can’t penetrate• Acids secreted by glands in skin- inhibit microbe growth• Sweat, saliva, tears- contain lysozyme- an enzyme that attacks

bacterial cell walls• Digestive and respiratory systems- guarded by mucous

membranes (b/c they are exposed to env)• Stomach acid- kills bacteria• Hair in nostrils- filters air• Mucous in respiratory system traps particles and cilia sweep

them out

Nonspecific defense cells• Neutrophils, monocytes and macrophages- engulf bact and

viruses• Natural killer cells- attack cancer cells and infected body cells

(especially those that harbor viruses)

Proteins also attack microbes or impede reproduction

• Interferons- proteins that are produced by cells that are infected by a virus to help other cells resist virus– Nonspecific, short term, can

be used to treat certain cancers

• Complement proteins- circulate in plasma, activated by immune system or microbes, stick to surfaces for macrophages to notice, cut holes in cells, amplify nonspecific responses

Inflammatory response

Inflammatory response• Major component of nonspecific defense• red, swollen, warm “inflamed” –due to increase in blood flow,

fluid and cells• Damaged skin releases chem signal (histamine)• It induces blood vessels to dilate and become leaky

– Blood flow to area increase, plasma moves to interstitial fluid

• Other chem’s attract phagocytes• Results: disinfect area, engulf bacteria• Clotting proteins- seal off infected region• Response can be local or systemic (WBC’s increase, fever, high

fever, low BP-septic shock)

The Lymphatic System• Returns tissue fluid to circ system and fight infection• Consists of: vessels, lymph nodes, tonsils, adenoids, appendix,

spleen, bone marrow, thymus• Involved in: nonspecific and specific resistance to infection• System is where fluid that has left circ system returns to,

happens by diffusion• Infection fighting occurs in lymph nodes and other vessels

which are packed with WBC’s– Sometimes they become swollen when fighting infection

The Lymphatic System

Specific Immunity• Immunity- resistance to specific invaders• Active- when antigens enter body (getting sick/a shot)• Passive- antibodies are passed (fetus from placenta,

sometimes when travelling to other countries)• Antigen- “antibody generating”- elicits immune response

– Molecules on surfaces of cells• Antibody- protein in blood plasma that attaches to particular

antigen and help counter its effect*****has a good memory*****

Lymphocytes

• White blood cells• Originate in bone marrow• Spend most of their time in tissues and organs

of lymphatic system• Produce specific immune responses• Response to antigens in 2 ways:

Lymphocytes • Mature in bone

marrow= B cells– Humoral immunity– Secretes antibodies– Can be transferred

passively (injecting antibodies)

• Mature in thymus =T cells– Cell-mediated

immunity– Attacks infected body

cells– Promotes phagocytosis

and stimulates B cells (so T cells are involved in both)

– Can be transferred passively (injecting T cells)

• Antigen receptors- molecules on cells surface, bind to antigen

100mil to 100bil different kinds of B and T cells!

Lymphocytes

Antigens • Most are proteins or polysaccharides• Antigenic determinants- region that antibody recognizes• Site on antibody (antigen-binding site)- recognizes

determinant– *complementary shape

Antigens • Activate lymphocytes to multiply that are specific to

the antigen- clonal selection– Effector cells produced secrete antibodies – This happens with B cells and T cells

Primary Immune Response• 1st time lymphocytes are exposed to antigen and clonal

selection happens– Takes a few days before lymphocytes are activated

Secondary Immune Response• After 2nd exposure to same

antigen– Produces very high antibody

levels, lasts longer– Each antigen exposure triggers

clonal selection– Cells of the clone include:– Memory cells- last for

decades, remain in lymph nodes, when activated-trigger secondary response, multiply quickly

– Effector cells- produce antibodies

Humoral vs. Cell-mediated Immunity

Humoral Immunity

• In body fluids• Effector cells produced during clonal selection

are called plasma cells• Plasma cells then secrete antibodies

Antibodies– 2 heavy chains and 2 light chains bonded together– 2 functions: recognize and bind to antigen & neutralize the antigen– Structure allows function– Antigen-binding sites in V region– Mark antigens for elimination– Binding creates antigen-antibody complex

Methods for antigen inactivation:• Neutralization- antibodies block antigens from binding with

cells, phagocytes engulf complex• Agglutination- “clumping” – clumps invaders together making

it easier for phagocytes to capture• Precipitation- link antigen molecules together and they

precipitate out of solution as solids, easily engulfed• Activation of complement proteins by antigen-antibody

complex- proteins open holes in plasma membrane, cell lyses

Monoclonal antibodies• Antibody secreted by a clone

of cells that’s specific for an antigen– Ex: pregnancy test- binds to

hormones, STD test-binds to bacteria

Cell-mediated Immunity– T cells respond to antigens on body’s own cells– Cytotoxic T cells- attack infected body cells– Helper T cells- help activate cytotoxic T’s and macrophages, and

stimulate B’s to produce antibodies– Antigen-presenting cells (APC’s) – present antigens to helper T’s-

triggering pathway to activate helper T’s

When a T cell is activated:– Grow and divide, producing more helper T and memory T cells– Stimulate cytotoxic T’s

• Bind to infected cells and form holes in membrane– Activate B cells– Cytotoxic T cells also can recognize changes in membranes of

cancerous cells and destroy them

Immune system depends on our molecular fingerprint

• Recognizes “self” and “non-self”• What if that doesn’t work?

Immune System Disorders• Autoimmune disease- immune system attacks body’s own

cells– MS, lupus, insulin-dependent diabetes

Immune System Disorders• Immunodeficiency disease- when a component of the system

is lacking– Can be caused by physical and emotional stressors– AIDS, SCID, Hodgkins disease– HIV virus destroys helper T cells

• Allergies- overreaction of the immune system– Antigens that cause allergies are called allergens