Chapter 23 Immune System

What You’ll Learn

You will describe how infections are transmitted and what causes the symptoms of diseases.

You will explain the various types of innate and acquired immune responses.

• You will compare antibody and cellular immunity

• Section Objectives:

• Describe how pathogens are transmitted.

• Explain what causes the symptoms of a disease.

23.1 Infectious diseases

What is an infectious disease?

• Disease-producing agents such as bacteria, protozoans, fungi, viruses, and other parasites are called pathogens. (NOT all microorganisms are pathogens

• main sources of pathogens are soil, contaminated water, and infected animals, including other people.

Reservoirs of pathogens

Transmission of disease

• Pathogens can be transmitted to a host from reservoirs in four main ways: by direct contact, by an object, through the air, or by an intermediate organism called a vector.

Transmission of disease II

• The common cold, influenza, and STDs are spread by direct contact.

Transmission of disease III• Bacteria and other

microorganisms can be present on nonliving objects such as money, toys, or towels.

• Transmission occurs when people unknowingly handle contaminated objects.

Transmission of disease IV

• Airborne transmission of a disease can occur when a person coughs or sneezes, spreading pathogens contained in droplets of mucus into the air.

Transmission of disease V• Diseases transmitted by

vectors are most commonly spread by insects and arthropods

• malaria and the West Nile virus are transmitted by mosquitoes.

• Lyme disease and Rocky Mountain spotted fever are diseases that are transmitted by ticks.

• Flies also are significant vectors of disease.

What causes the symptoms of a disease?

• When a pathogen invades your body, it encounters your immune system.

• If the pathogen overcomes the defenses of your immune system, it can metabolize and multiply, causing damage to the tissues it has invaded, and even killing host cells

Damage to the host by viruses and bacteria

• Most of the damage done to host cells by bacteria is inflicted by toxins.

• These poisons can inhibit protein synthesis in the host cell, destroy blood cells and blood vessels, produce fever, or cause spasms by disrupting the nervous system.

Patterns of Diseases

• Some diseases, such as typhoid fever, occur only occasionally in the United States.

• On the other hand, many diseases are constantly present in the population-endemic disease. Ex. Common cold

Treating Diseases

• 1 way: An antibiotic is a substance produced by a microorganism that, in small amounts, will kill or inhibit the growth and reproduction of bacteria.

• Your body also has its own built-in defense system— the immune system —that works to keep you healthy.

• Section Objectives:• Identify the cells, tissues, and organs that

make up the immune system.

• Compare innate( nonspecific) and acquired (specific)immune responses.

• Distinguish between antibody and cellular immunity.

• Summarize the structure of the lymphatic system

• Distiguish between passive and active immunity

23.2 The Immune System

Lines of defense• 1st line:– broad, external defense

• “walls & moats” – skin & mucus membranes

• 2nd line:– broad, internal defense

• “patrolling soldiers”– phagocyte (eating) WBCs

• 3rd line:– specific, acquired immunity

• “elite trained units”– lymphocyte WBCs & antibodies

• B & T cells

Barriers

Non-specific patrol

Immune system

Innate Immunity

• The body’s earliest lines of defense against any and all pathogens make up your nonspecific, innate immunity.

Nonspecific defense I• 1st line of defense:• Skin Intact skin is a

formidable physical barrier to the entrance of microorganisms

• Body secretions mucus traps many microorganisms

• Sweat, tears, and saliva all contain the enzyme lysozyme, which is capable of breaking down the cell walls of some bacteria

Lining of trachea: ciliated cells & mucus secreting cells

Nonspecific defense II• 2nd line of defense • Inflammation(Inflammatory response) characterized by

four symptoms—redness, swelling, pain, and heat; histamine released causes blood vessels in the injured area to dilate,(redness) which makes them more permeable to tissue fluid. Fluid that leaks from the vessels helps the body destroy toxic agents and restore homeostasis (swelling and pain,&heat)

Nonspecific defense V• After a few days, infected

tissue harbors a collection of live and dead white blood cells, multiplying and dead pathogens, and body fluids called pus.

• Pus formation usually continues until the

infection subsides.

• Eventually, the pus is cleared away by macrophages.

PusPhagocytes

Swelling

occurs

Tissue fluid moves

into injured area

Nonspecific defense III• 2nd line of defensePhagocytosis of

pathogens white blood cells that destroy pathogens by surrounding and engulfing them.

• Macrophages are white blood cells that provide the first defense against pathogens that have managed to enter the tissues.

Macrophage “eating” bacteria

Phagocytes

yeastmacrophage

macrophage

bacteriawhite blood cells that eat

Fever

• When a local response is not enough– full body response to infection– raises body temperature – higher temperature helps in defense• slows growth of germs• helps macrophages• speeds up repair of tissues

Nonspecific defense IV

• Phagocytosis of pathogens• If the infection is not stopped by the tissue

macrophages, another type of phagocyte, called a neutrophil is attracted to the site.

• If the infection is not stopped by tissue macrophages and neutrophils -

Monocytes

Nonspecific defense VI

• Protective proteins:• Interferons are proteins that protect cells

from viruses.

• Complement: help attract phagocytes to foreign cells and help destroy foreign cells

• Natural Killer cells:type of white blood cell that destroy the body's own infected cells, may attack cells that form tumors

The lymphatic system

• The lymphatic system becomes a crucial battleground during infection

• a network of lymphatic vessels and organs– It returns tissue fluid to the

circulatory system– It fights infections

• Lymph nodes are key sites for fighting infection– They are packed with

lymphocytes and macrophages

Acquired Immunity

• Defending against a specific pathogen by gradually building up a resistance to it

• This acquired immune response enables these white blood cells to inactivate or destroy the pathogen.

• Acquired immunity involves the production of two kinds of immune responses: antibody immunity and cellular immunity ~

• your 3rd line of defense

Acquired Immunity

• SPECIFIC IMMUNITY• IMMUNE RESPONSE a recognition system that distinguishes “self” from

“non-self”• responds to foreign molecules called antigens• Stimulates the body to make antibodies: specific defensive proteins which help to counter

antigens in various ways

How are invaders recognized?• Antigens– chemical name tags on the surface of

every cell• “self” vs. “invader”

disease-causingbacteria

disease-causingvirus

one of yourown cells

antigens say:“I belong here”

antigens say:“I am an invader”

antigens say:“I am an invader”

3rd line of defenseLymphocytes ~type of white blood cell that carry

out the immune response• Two kinds– B cells secrete antibodies

that attack antigens (antibody immunity)

– T cells attack cells infected with pathogens (cellular immunity)

B lymphocyte

B cells & antibodies• B cells– white blood cells that attack

invaders in blood– mature in Bone marrow

• Patrolling B cells – make antibodies against invader immediately

• Memory B cells– remembers invader– can make antibodies quickly the next time• protects you from getting disease more than once

• Proteins made by B cells that tag invaders in the blood so macrophages can eat them– tag says “this is an invader” gotcha!

• biological “handcuffs”– antibody attaches to antigen of invader

Antibodies

macrophageeating tagged invaders

invading germs tagged with antibodies

Y

Y

YY

YY

Y

B cells releasing antibodies

Y

YY

Y

Y

Y

Y

Y Y

Y

Y

Y

Y

Y

Antibody Immunity

• An antibody molecule has antigen-binding sites specific to the antigen

• Do not posses the power to destroy antigens directly, tag and mark them for destruction by a variety of mechanisms

B cells immune responseinvader(foreign antigen)

Y

Y

Y

Y

B cellsY

Y

Y

Y

Y

YY

Y

Y

Y

Y

Y

Y

Y

Y

YY

Y

Y

Y

Y

Y

Y

YY

Y

Y

Y

“reserves”

memory B cells

Y

Y

Y

Y

Y

YY

YY

YY

Y

Y

B cellsrelease antibodiespatrol bloodforever

recognition

10 to 17 days

YY

Y

Y

YY Y

YY

Y

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YYY

YYY

Y

Y

T cells• T cells mature in Thymus• Helper T cells – sound the alarm for rest

of immune system

• Killer T cells– destroy infected body cells

• Memory T cells– remembers invader & reacts against

it again quicklyWhere’s that?

Attack of the Killer T cells• Killer T cells destroy infected body cells– T cell binds to invaded cell– secretes perforating protein• punctures cell membrane of infected cell• cell bursts

Perforin puncturescell membrane

cell membrane

Killer T cell

cell membrane

invaded cell

vesicle

2006-2007

What if the attacker gets past the B cells in the blood &

infects some of your cells?You need trained assassins to kill

off these infected cells!

T

Attackof the Killer T cells!

Cellular Immunity

Pathogen

engulfed by

MacrophageDisplays antigens

on surface and

stimulates T cell

Helper T cell

Stimulates

Cytotoxic T cell

Attacks infected

cell

Cytotoxic T cell

Foreign

antigen

Infected cells

Perforin

Infected cell lyses

Immune responseinvader

invaders in blood invaders infect cells

B cells T cells

macrophages

helperT cells

patrollingB cells

memoryB cells

memoryT cells

killerT cells

YYY

Y

YY

Y

YantibodiesY

Y Y

skinskininvaders in body

YY

Y

Y

YY

Y

YantibodiesY

Y Y

Passive and Active Immunity

• Acquired immunity to a disease may be either passive or active.

Passive Immunity

Passive: short term, antibodies passed on, not stimulated by antigens,

acquired naturally by placenta or breast milk or

artificially acquired by a shot

Active Immunity

1. Active: long term, conferred by actual encounter with infection (naturally acquired) or vaccination *(artificially acquired)

* vaccine~ substance consisting of weakened, dead, ,or parts of pathogen or antigen that when injected , stimulates the immune system

23.3 Noninfectious disorders

Section objective:•Describe categories od noninfectious disease

Noninfectious disorders

Genetic disorders•Caused by the inheritance of genes that do not function properly• ex: sickle cell anemia, hemophilia, cystic fibrosis

Noninfectious disorders

• Degenerative diseases~ result of a part of the body wearing out ex: degenerative arthritis

• Metabolic diseases~ results in an error in a biochemical pathway

• Cancer~ abnormal cell growth

DISORDERS OF THE IMMUNE SYSTEM

• Allergies are overreactions to certain environmental antigens called

allergens : Ex. Animal dander, dust mites, pollen

release of histamine causes symptoms: sneezing, increased mucus production in the nasal passages, and redness.

Antihistamines can relieve symptoms

DISORDERS OF THE IMMUNE SYSTEM

• Autoimmune diseases

immune system also can mistakenly attack the body’s own tissues – Examples: Rheumatic

fever, Type I Diabetes, Multiple Sclerosis, Rheumatoid arthritis, Lupus

Rheumatoid arthritisRheumatoid arthritis

DISORDERS OF THE IMMUNE SYSTEM

• Immunodeficiency diseases– Immune components

are lacking, and infections recur

Ex: Acquired immune deficiency syndrome (AIDS)

SCIDS

HIV on a lymphocyte

AIDS

– HIV (Human Immunodeficiency Virus) the virus that causes AIDS

– HIV is transmitted mainly in blood and semen

– HIV kills helper T-cells and leads to AIDS

Attacking transplanted tissue.

• T cells and antibodies also can attack transplanted tissue, such as a transplanted kidney, that comes from a source outside the body.