The Immune SystemThe Immune System

Nonspecific vs. specific Nonspecific vs. specific defensesdefenses

NonspecificNonspecific defenses do not defenses do not distinguish one infectious microbe distinguish one infectious microbe from anotherfrom another

SpecificSpecific defenses recognize and defenses recognize and defend against invading microbes defend against invading microbes and cancer cellsand cancer cells

Nonspecific defensesNonspecific defenses

Skin is a barrier that most bacteria Skin is a barrier that most bacteria and viruses can’t penetrateand viruses can’t penetrate Acids secreted by skin prohibit growth of Acids secreted by skin prohibit growth of

many microbesmany microbes Sweat, saliva, and tears contain Sweat, saliva, and tears contain

enzymes that attack bacterial cell wallsenzymes that attack bacterial cell walls Mucus produced in digestive and Mucus produced in digestive and

respiratory systems also protects respiratory systems also protects against microbesagainst microbes

Nonspecific defensesNonspecific defenses

Microbes that penetrate skin, digestive, Microbes that penetrate skin, digestive, or respiratory systems face neutrophils or respiratory systems face neutrophils and monocytesand monocytes macrophages that “eat” bacteria and macrophages that “eat” bacteria and

virusesviruses Interferons and complement proteins Interferons and complement proteins

attack microbes either directly or attack microbes either directly or indirectly by impeding their indirectly by impeding their reproductionreproduction

Nonspecific defensesNonspecific defenses

Interferons are produced by infected Interferons are produced by infected cells cells Diffuse to healthy cells where they Diffuse to healthy cells where they

cause the cell to inhibit viral productioncause the cell to inhibit viral production Complement proteins are activated Complement proteins are activated

by microbes or immune systemby microbes or immune system Coat infected cells –easier to eatCoat infected cells –easier to eat Can amplify inflammatory responseCan amplify inflammatory response

Nonspecific defenses: Nonspecific defenses: inflammatory responseinflammatory response

Nonspecific defenses: Nonspecific defenses: inflammatory responseinflammatory response

Redness, heat, and swelling caused Redness, heat, and swelling caused byby Increase in blood flow, fluid, and cellsIncrease in blood flow, fluid, and cells

Inflammatory response disinfects and Inflammatory response disinfects and cleans injured tissuescleans injured tissues Pus = dead white cells and fluidPus = dead white cells and fluid

Systemic response is widespreadSystemic response is widespread Toxins or microorganisms released in Toxins or microorganisms released in

bloodstreambloodstream Circulates through bodyCirculates through body

Nonspecific defenses: Nonspecific defenses: inflammatory responseinflammatory response

Systemic response cont’d.Systemic response cont’d. Inflammatory weapons: increase white Inflammatory weapons: increase white

blood cells, feverblood cells, fever Low-grade fever can stimulate phagocytosis Low-grade fever can stimulate phagocytosis

and inhibit growth of many microorganismsand inhibit growth of many microorganisms

Lymphatic systemLymphatic system

Lymphatic systemLymphatic system Involved in both specific and nonspecific Involved in both specific and nonspecific

responsesresponses Lymphatic system defenses occur in Lymphatic system defenses occur in

lymph nodes and lymphatic system organslymph nodes and lymphatic system organs Packed with lymphocytes and macrophagesPacked with lymphocytes and macrophages Lymph carries microbes from infection sites Lymph carries microbes from infection sites

and some cancer cellsand some cancer cells In the lymphatic organs, macrophages may In the lymphatic organs, macrophages may

“eat” the invaders (nonspecific)“eat” the invaders (nonspecific) Lymphocytes can be involved in specific Lymphocytes can be involved in specific

immune responseimmune response

Specific immunitySpecific immunity Often more effective than nonspecific Often more effective than nonspecific

responseresponse It also amplifies nonspecific responseIt also amplifies nonspecific response

Specific response begins due to presence of Specific response begins due to presence of an antigenan antigen Can either increase number of cells that attack Can either increase number of cells that attack

invader directly ORinvader directly OR Produce antibodiesProduce antibodies

Immune system “remembers” antigens it Immune system “remembers” antigens it has previously encounteredhas previously encountered Responds immediately and vigorously Responds immediately and vigorously Is adaptiveIs adaptive

LymphocyteLymphocytess

Specific Immunity: Specific Immunity: LymphocytesLymphocytes

Humoral systemHumoral system defends against defends against bacteria and viruses present in body bacteria and viruses present in body fluidsfluids Fluids: blood, lymph, and interstitial fluid Fluids: blood, lymph, and interstitial fluid Antibodies, Antibodies, secreted by B cellssecreted by B cells and and

dissolved in the blood, are carried in dissolved in the blood, are carried in lymph and blood to sites of infectionslymph and blood to sites of infections

Cell-mediated immunityCell-mediated immunity T-cells circulate in blood and lymph T-cells circulate in blood and lymph Attack body cellsAttack body cells that have been infected that have been infected

Specific Immunity: Specific Immunity: LymphocytesLymphocytes

For BOTH humoral and cell-mediated For BOTH humoral and cell-mediated immunityimmunity B & T cells have antigen receptors B & T cells have antigen receptors

(antibodies) that protrude from cell (antibodies) that protrude from cell surface surface

specific for one type of antigen**specific for one type of antigen** Each person has between 100 million to Each person has between 100 million to

100 billion different kinds of B & T cells!100 billion different kinds of B & T cells!

AntigensAntigens

Most antigens are molecules that are Most antigens are molecules that are present on viral surfaces or foreign present on viral surfaces or foreign cellscells

B cells respond to free antigens in B cells respond to free antigens in body fluidbody fluid

Different antibodies can bind to the Different antibodies can bind to the same antigensame antigen

Specific immunity: clonal Specific immunity: clonal selectionselection

Primary vs. Secondary immune Primary vs. Secondary immune responseresponse

Role of T cells in ImmunityRole of T cells in Immunity

T cells battle pathogens that have T cells battle pathogens that have already entered body cellsalready entered body cells Respond to antigens that have bonded Respond to antigens that have bonded

to body cell surfacesto body cell surfaces Mount cell-mediated defense and aid Mount cell-mediated defense and aid

humoral immunityhumoral immunity

T cellsT cells Cytotoxic T cellsCytotoxic T cells

Only T cells that kill other cellsOnly T cells that kill other cells Synthesize a protein that ruptures infected Synthesize a protein that ruptures infected

cellcell

Helper T cellsHelper T cells Secrete stimulatory proteins that helpSecrete stimulatory proteins that help

Promote production of more helper T cells Promote production of more helper T cells and memory cellsand memory cells

Activate cytotoxic T cellsActivate cytotoxic T cells Stimulate B cells to produce antibodiesStimulate B cells to produce antibodies

Autoimmune DiseasesAutoimmune Diseases

MS: T cells attack myelin –a protein MS: T cells attack myelin –a protein that insulates the axons of neurons that insulates the axons of neurons (a brain thing)(a brain thing) Most common chronic neurological Most common chronic neurological

disease in developed countriesdisease in developed countries

Immunodeficiency diseasesImmunodeficiency diseases

SCID (Severe Combined SCID (Severe Combined Immunodeficiency): T and/or B cells are Immunodeficiency): T and/or B cells are absent or inactiveabsent or inactive ““bubble” peoplebubble” people

AllergiesAllergies

Stage 1 Stage 2

HIV/AIDSHIV/AIDS

HIV destroys the immune system by HIV destroys the immune system by infecting helper T cellsinfecting helper T cells

Eventually develop AIDSEventually develop AIDS Body cannot carry out cell-mediated or Body cannot carry out cell-mediated or

humoral response humoral response Die from opportunistic infectionsDie from opportunistic infections

36.1 million people have HIV/AIDS36.1 million people have HIV/AIDS 5.3 million new cases each year5.3 million new cases each year