ImmunitImmunityy

Chapter 48Chapter 48

April SikeApril Sike

AP Biology AP Biology

April, 2011April, 2011

SummarySummaryWe survive because we have evolved a We survive because we have evolved a

variety of defenses against constant variety of defenses against constant attack. The first line of defense attack. The first line of defense consists the mechanisms for consists the mechanisms for preventing bacteria from entering the preventing bacteria from entering the body. The second line of defense body. The second line of defense consists mechanisms for dealing with consists mechanisms for dealing with any foreign substances in the body. All any foreign substances in the body. All organisms have the mechanics to organisms have the mechanics to protect themselves from the protect themselves from the onslaught of smaller organisms and onslaught of smaller organisms and viruses.viruses.

Evolutionary Evolutionary developmentdevelopment

• InvertebratesInvertebrates

• VertebratesVertebrates

InvertebratesInvertebrates• In 1882 Elie Metchnikoff became the In 1882 Elie Metchnikoff became the

first to recognize that invertebrate first to recognize that invertebrate

animals have immune defenses.animals have immune defenses.

• The invertebrate immune response The invertebrate immune response

shares several elements with the shares several elements with the

vertebrate one.vertebrate one.

PhagocytesPhagocytes

• All animals have All animals have phagocyticphagocytic cellscells that that

attack invading microbes. attack invading microbes.

• These cells travel through the animal’s These cells travel through the animal’s

circulatory system.circulatory system.

• In animals that do not have a In animals that do not have a

circulatory system the phagocytic cells circulatory system the phagocytic cells

roam inside the mesoglea.roam inside the mesoglea.

Distinguishing Self from NonselfDistinguishing Self from Nonself• The ability to recognize the difference between cells The ability to recognize the difference between cells

of your own body and cells from another individual of your own body and cells from another individual

seems to have evolved early in the history of life.seems to have evolved early in the history of life.

• Sponges, thought to be the most ancient animals, Sponges, thought to be the most ancient animals,

attack tissues from other sponges just like insects attack tissues from other sponges just like insects

and starfish.and starfish.

• None of these invertebrates seem to show any None of these invertebrates seem to show any

evidence of having an immune system.evidence of having an immune system.

• Apparently the humoral immune defense did not Apparently the humoral immune defense did not

evolve until vertebrates.evolve until vertebrates.

LymphocytesLymphocytes

• LymphocyteLymphocyte – A type of white blood cell – A type of white blood cell responsible for the immune responses, two responsible for the immune responses, two classes; classes; B cells and T cells.B cells and T cells.

• Invertebrates do not have complementary proteins Invertebrates do not have complementary proteins or lymphocytes.or lymphocytes.

• But annelid earthworms and other invertebrates But annelid earthworms and other invertebrates do have lymphocyte-like cells that may be do have lymphocyte-like cells that may be evolutionary precursors of lymphocytes.evolutionary precursors of lymphocytes.

B and T cellsB and T cells• B cells:B cells: B cells respond to helper T B cells respond to helper T

cells by interleukin-1. B cells have cells by interleukin-1. B cells have receptor proteins on their surface, one receptor proteins on their surface, one type of receptor for each type of B cell.type of receptor for each type of B cell.

• T CellsT Cells: : protect the body from virus infection and cancer, by killing abnormal cells.

B Cells: B Cells: The Humoral Immune The Humoral Immune ResponseResponse

• In this response, the immune system In this response, the immune system

triggers specific B cells to make large triggers specific B cells to make large

amounts of their specific antibodies. amounts of their specific antibodies.

These antibodies can fight viruses and These antibodies can fight viruses and

stop infection.stop infection.

• http://bcs.whfreeman.com/thelifewire/http://bcs.whfreeman.com/thelifewire/content/chp18/1802004.htmlcontent/chp18/1802004.html

T Cells: T Cells: Cellular Immune Cellular Immune ResponseResponse

• Cells of this system kill cells of the body Cells of this system kill cells of the body

that are cancerous. This response relies on that are cancerous. This response relies on

the lethal cytotoxic T cells. They contain the lethal cytotoxic T cells. They contain

molecules, called perforin, that they release molecules, called perforin, that they release

into target cells. The perforin pokes holes into target cells. The perforin pokes holes

in the target cells and kills them.in the target cells and kills them.• http://bcs.whfreeman.com/thelifewire/http://bcs.whfreeman.com/thelifewire/

content/chp18/1802003.htmlcontent/chp18/1802003.html

• The earliest vertebrates, the jawless The earliest vertebrates, the jawless lampreys first evolved some 500 million lampreys first evolved some 500 million years ago.years ago.

• They have an immune system based onThey have an immune system based on

lymphocytes.lymphocytes.

• At this early stage of vertebrate evolution, At this early stage of vertebrate evolution, however, lampreys lack distinct however, lampreys lack distinct populations of B and T cells that are found populations of B and T cells that are found in all higher vertebrates.in all higher vertebrates.

VertebratesVertebrates

• The modern vertebrate immune system first The modern vertebrate immune system first

arose with the evolution of fish with jaws.arose with the evolution of fish with jaws.

• The oldest surviving group of jawed fishes are The oldest surviving group of jawed fishes are

the sharks, which evolved 450 million years the sharks, which evolved 450 million years

ago. By then the vertebrate immune defense ago. By then the vertebrate immune defense

had been fully evolved.had been fully evolved.

• Sharks have an immune response similar to Sharks have an immune response similar to

mammals, with a cellular response carried out mammals, with a cellular response carried out

by T cell lymphocytes and humoral response by T cell lymphocytes and humoral response

carried out by B cells.carried out by B cells.

NecessaryNecessary

• The Immune system is necessary for survival because The Immune system is necessary for survival because

without it organisms would not be able to protect without it organisms would not be able to protect

themselves against viruses or diseases. We would be themselves against viruses or diseases. We would be

subject to every infection and disease and not survive.subject to every infection and disease and not survive.

• There is no example in the world of an organisms There is no example in the world of an organisms

functioning without an immune system, but there are functioning without an immune system, but there are

examples of organisms being born without specific examples of organisms being born without specific

parts of their immune system, making them susceptible parts of their immune system, making them susceptible

to infection by certain types of virusesto infection by certain types of viruses..

Structures and functions of the Structures and functions of the systemsystem

• Skin: Skin: The first line of defenseThe first line of defense

• Cellular Counterattack: Cellular Counterattack: 22ndnd line of defense line of defense

• The Immune Response: The Immune Response: 33rdrd line of defense line of defense

Skin: 1Skin: 1stst line of defense line of defense• The largest organ of the vertebrate body, The largest organ of the vertebrate body,

provides nearly impenetrable barriers and provides nearly impenetrable barriers and reinforces defenses with surface chemical reinforces defenses with surface chemical weapons.weapons.

• Mucus membranes of the digestive, and Mucus membranes of the digestive, and reparatory help trap and get rid of reparatory help trap and get rid of microorganisms before they invade the microorganisms before they invade the body’s tissue.body’s tissue.

Cellular counterattack: 2Cellular counterattack: 2ndnd line of line of defensedefense

• MacrophagesMacrophages – big phygocytic cells that can – big phygocytic cells that can

digest invading bacteria.digest invading bacteria.

• Cellular and chemical defenses respond to Cellular and chemical defenses respond to

any microbial infection.any microbial infection.

• NeutrophilsNeutrophils (capable of engulfing (capable of engulfing

microorganisms and other foreign particles) microorganisms and other foreign particles)

kill cells of the body infected with viruses.kill cells of the body infected with viruses.

The Immune Response: 3The Immune Response: 3rdrd line line of defenseof defense

• The pathogen enters the body.The pathogen enters the body.

• Macrophages with antigen fragments displayed on Macrophages with antigen fragments displayed on their surfaces are called their surfaces are called antigen-presenting cellsantigen-presenting cells. . An antigen-presenting macrophage interacts with An antigen-presenting macrophage interacts with a T-helper cell that can recognize the same a T-helper cell that can recognize the same antigen.antigen.

• During the interaction, the macrophage releases a During the interaction, the macrophage releases a chemical alarm signal called interleukin-1, which chemical alarm signal called interleukin-1, which stimulates the T-helper cell to secrete interlukin-2. stimulates the T-helper cell to secrete interlukin-2.

The Immune response

1.) Damaged tissues release histamines, increasing blood flow to the area.

3.) Phagocytes engulf bacteria, dead cells, and cellular debris.

2.) Histamines cause capillaries to leak, releasing phagocytes and clotting factors into the wound.

4.) Platelets move out of the capillary to seal the wounded area.

Interdependence of this system Interdependence of this system with other body systemswith other body systems

The immune system works closely with theThe immune system works closely with the

circulatory systemcirculatory system for transportation needs by for transportation needs by

means of blood cells, allowing the immune cells tomeans of blood cells, allowing the immune cells to

travel throughout the body and survey the body fortravel throughout the body and survey the body for

infection. The infection. The nervous systemnervous system uses the brain to uses the brain to

help stimulate the defense mechanisms againsthelp stimulate the defense mechanisms against

infection, and the infection, and the skeletal systemskeletal system provides the provides the

blood cells that the immune system needs.blood cells that the immune system needs.

The immune System & The The immune System & The Lymph  SystemLymph  System

• Lymph organs include the bone marrow, lymph Lymph organs include the bone marrow, lymph

nodes, spleen, and thymus. Bone marrow contains nodes, spleen, and thymus. Bone marrow contains

tissues that produce lymphocytes. tissues that produce lymphocytes.

• B-cells mature in the bone marrow. B-cells mature in the bone marrow.

• T-cells mature in the thymus gland.T-cells mature in the thymus gland.

• Other blood cells like monocytes and leukocytes are Other blood cells like monocytes and leukocytes are

made in the bone marrow. made in the bone marrow.

• The thymus makes the hormone; The thymus makes the hormone; thymosinthymosin, that , that

causes T-cells to mature in the thymus.causes T-cells to mature in the thymus.

3 types of diseases or disorders 3 types of diseases or disorders of the systemof the system

• T Cell DestructionT Cell Destruction

• Antigen ShiftingAntigen Shifting

• Autoimmunity and AllergyAutoimmunity and Allergy

T Cell DestructionT Cell Destruction

• Many helper T Cells and inducer T cells Many helper T Cells and inducer T cells are CD4+ T cells. Therefore, any are CD4+ T cells. Therefore, any pathogen that inactivates CD4+ T cells pathogen that inactivates CD4+ T cells leave the immune system unable to mount leave the immune system unable to mount a response from any foreign antigen.a response from any foreign antigen.

Antigen ShiftingAntigen Shifting

• A pathogen may escape recognition by A pathogen may escape recognition by

the immune system if it changes its the immune system if it changes its

surface antigens. Such antigen shifting is surface antigens. Such antigen shifting is

an example of evolution by natural an example of evolution by natural

selection.selection.

Autoimmunity and AllergyAutoimmunity and Allergy• Autoimmunity diseases are produced by Autoimmunity diseases are produced by

failure of the immune system to failure of the immune system to recognize and tolerate self-antigens, and recognize and tolerate self-antigens, and can result from a variety of mechanisms.can result from a variety of mechanisms.

• Allergies can be divided into immediate Allergies can be divided into immediate hypersensitivity and delayed hypersensitivity and delayed hypersensitivity, both of which can cause hypersensitivity, both of which can cause the release of histamine.the release of histamine.

• In extreme cases, the widespread release In extreme cases, the widespread release of histamine can lead to anaphylactic of histamine can lead to anaphylactic shock.shock.