chapter 26: immunity and health how the body defends and maintains itself lecture by danielle...

Chapter 26: Immunity and Health

How the body defends and maintains itselfLecture by Danielle DuCharme, Waubonsee Community College

Learning Objectives

• Understand how the body protects you against disease-causing invaders.

• Describe how immunity develops after exposure to the pathogen.

• Show how disease results from the malfunction of the immune system.

26.1 Three lines of defense prevent and fight pathogen attacksMany of us to do not consider pathogens (disease-causing microorganisms) or their effects until we hear an illness is “going around.”

Example: H1N1

Microscopic Organisms

The vast majority of microscopic organisms found on everyday items will not cause disease, but some will.

The Immune SystemThe human immune system provides protection against an enormous variety of pathogens, including many bacteria, fungi, viruses and parasitic protists and worms.

Immune System Protection*

To accomplish this challenging protective task, there are three major divisions of the immune system:

1. Physical barriers2. Non-specific immunity 3. Specific immunity

The Three Divisions of the Immune System Are Collaborative

Take-Home Message 26.1

• The immune system protects us from a diverse group of pathogens.

• There are three collaborative divisions to the immune system: a physical barrier, non-specific immunity, and specific immunity.

Take-Home Message 26.1

• Physical immunity and non-specific immunity are the first lines of defense and, as non-specific systems, recognize pathogens only as “non-self.”

Take-Home Message 26.1

• The specific immunity line of defense recognizes individual species of pathogens and forms a memory of them.

26.2 External barriers prevent pathogens from entering your bodyYour body has ways to prevent pathogens from entering your body, tissues and cells.

The Integumentary System

The integumentary system is made up of skin, sweat glands, oil glands, hair and nails that protect you from mechanical stress caused by external forces such as pressure, sunlight, dehydration, and, of course, pathogens.

Toilet Seats—Hidden Danger?

The good news is that human pathogens cannot survive outside the body for very long.

And, pathogens need an access point.

Defense Mechanism

s

Skin Is Far More Active Than a Protective Wall

• Skin cells actively secrete chemicals that inhibit bacterial growth.

• A lysozyme is an enzyme that can kill bacteria by damaging cell walls.

The Respiratory Tract Is Protected by Mucus

In the respiratory tract, hair-like extensions of the epithelial cells, called cilia, continually move mucus-entrapped pathogens up and out of the lungs.

Protecting the Eyes

• Eyes produce tears that physically wash away microorganisms

• Tears also contain lysozyme and antiviral and antibacterial chemicals.

Protecting the Ears

• The physical properties of ear wax are effective at trapping microorganisms.

• The slight acidity and the lysozyme in ear wax also serve to inhibit the growth of some microorganisms that find their way into the ear canal.

Take-Home Message 26.2

• Skin, part of the integumentary system, is a physical barrier that prevents pathogens from entering the body’s cells.

Take-Home Message 26.2

• Cells that are not covered by skin but are exposed to the external environment are protected by defenses such as bacteria-destroying chemicals, acidic secretions, sticky mucus, and wax.

26.3 The non-specific division of the immune system recognizesand fights pathogens while signaling for additional defenses.

Your body will recognize a “security breach” and respond to prevent infection.

Responding to Pathogens

• Recognition• Call for “backup”

Cellular Communication

The chief way that cells of the immune system talk to one another is by secreting signaling proteins called cytokines.

Cytokines

Cytokines secreted by one immune cell can bind to receptors on other immune cells and signal them to respond in various ways.

– For example, to recruit more immune cells to the site of infection.

Interferon

• an important type of cytokine produced by cells infected by a virus

• alerts other cells to turn on protective measures that help them resist viruses

White Blood Cells

• specialized cells that play roles in both the specific and the non-specific divisions of the immune system

• made in the bone marrow and released into the bloodstream, where they patrol the body’s tissues and search for invaders.

White Blood Cells

Phagocytes

White blood cells that can engulf, ingest, kill, and break down foreign pathogens and particles.

Three Types of White Blood Cells

• neutrophils • macrophages • dendritic cells

All act as phagocytes, with the dendritic cells also having an important role in stimulating the specific immunity system.

Neutrophils

• circulate in the blood and exit blood vessels at sites of injury and infection in tissues

• ingest small organisms, primarily bacteria

• produce hydrogen peroxide and bleach

Pus

In the process of killing, neutrophils destroy themselves and become a major part of pus, the thick yellowish fluid we often notice at the site of infection.

Antiseptic

A solution used on a body surface to kill or discourage growth of microorganisms, such as rubbing alcohol or hydrogen peroxide.

Macrophages

• large white blood cells that reside in and patrol the tissues

• engulf and digest whole pathogens, as well as any debris that remains after the neutrophils have done their job

Dendritic Cells

• phagocytes that link the non-specific and specific divisions of the immune system by “presenting” the cells of the specific system with foreign matter

• migrate to the lymph nodes, which are populated by cells of the specific immunity system

Fourth Type of White Blood Cells

Natural killer (NK) cells are not phagocytes, but operate by killing body cells that have been infected by pathogens.

Natural Killer Cells

Natural killer (NK) cells, which are not phagocytes, provide the first line of resistance to viruses by poking holes in the membranes of virus-infected cells so as to kill the cells, and in doing so, killing the viruses inside the cells.

Complement Proteins

The nonspecific system can also quickly recognize and destroy invaders thanks to some circulating defensive proteins, collectively called complement proteins.

Take-Home Message 26.3

• Non-specific immunity provides defenses against pathogens by recognizing molecules on their cell surfaces.

• Immune cells communicate with each other via chemical signals called cytokines.

Take-Home Message 26.3

• Non-specific immunity cells that secrete cytokines can recruit other cells to the site of infection or warn them to protect themselves.

Take-Home Message 26.3

• White blood cells of the non-specific system include phagocytes—such as neutrophils and macrophages that ingest and kill pathogens, and macrophages and dendritic cells that display pathogens to cells of the specific immunity system—and natural killer cells, which kill virus-infected cells and cancer cells.

Take-Home Message 26.3

• Complement proteins also non-specifically recognize invaders and help to destroy them.

26.4 The non-specific system responds to infection with theinflammatory response and with fever.The inflammatory response is a combination of events that leads to recruitment of phagocytes and other immune cells to assist with pathogen destruction, followed by tissue healing.

Inflammatory Response

• Invading pathogens from the invading body and the skin surface are quickly engulfed by the macrophages that reside in all tissues.

• The macrophages then release cytokines to recruit more phagocytes and two other types of white blood cells, which initiate inflammation.

Basophils and Mast Cells Trigger Histamine Release

Basophils, which circulate in the blood, and mast cells, found in the tissues, trigger the inflammatory reaction by releasing histamine.

Histamine Reaction

• The increased blood supply at the site of injury causes the redness and heat associated with inflammation.

• The increased leakiness of the blood vessels makes it easier for neutrophils to exit the blood and enter tissue at the site of infection to begin destroying any invading pathogens.

Pain

• Macrophages and neutrophils then begin an immediate response to destroy pathogens and also release cytokines.

• Some of the cytokines released from macrophages, neutrophils, and mast cells can activate neurons and are therefore are the cause of pain.

Complement Proteins

Activated complement proteins at the site of infection cause mast cells to release histamine, and further amplify the inflammatory response by attracting additional phagocytes.

Scabs

• A scab temporarily forms to cover the wound, much like a natural Band-Aid, and prevents more pathogens from entering.

• At the end of the inflammatory process, collagen fibers are secreted by nearby cells to close the wound in a more stable fashion, and the scab falls off.

Fever

Some cytokines can cause a fever, an elevated body temperature, if their concentration is high enough.

Take-Home Message 26.4

• Inflammation is a major way in which pathogens are eliminated by the non-specific (innate) immunity system.

Take-Home Message 26.4

• The four recognizable signs of the inflammatory response (redness, heat, swelling, and pain) are related to the changes in blood vessels that enhance the recruitment of phagocytes and complement proteins to the site of inflammation.

Take-Home Message 26.4

• Fever-promoting cytokines cause the hypothalamus to set the body temperature higher, which may help the body fight an infection by stimulating the immune responses and inhibiting the growth of some pathogens.

26.5 The specific division of the immune system forms a memory of specific pathogens.

• the recognition is more specific• different types of cells and molecular

weapons are used• There is a trade-off between the speed

of the non-specific response and the slower, but much more precise, response of the specific immunity system.

Specific Immunity System

• The specific immunity system forms a memory, so the body’s response to a specific pathogen occurs more quickly in future encounters.

• The memory of the specific division of the immune system results in immunity, a state of long-term protection against a specific pathogen.

There are two ways to acquire immunity

• The first is to become sick with the disease.• The second is to be inoculated with a vaccine.

Vaccines

• A vaccine is a weakened or harmless form of a specific pathogen that is administered to an individual to induce immunity, without subjecting the individual to the disease.

• Vaccines trick the body into thinking it has the full-blown disease, and the body mounts a specific immunity response.

Antigens and Antibodies

• An antigen is any molecule that induces a specific immune response.

• The body responds to antigens by making antibodies, circulating proteins that recognize specific antigens.

Antibodies

• Provide protection by enhancing the non-specific system’s ability to recognize and destroy bacteria or viruses and the body cells they infect

Get A Flu Shot Every Year . . .

A Moving Target

• Just like the influenza virus, the rhinovirus (“nose virus”) continually changes.

• Each time you catch a cold, you are reacting to a different version of the same virus or an entirely new virus.

Take-Home Message 26.5

• Long-term protection from, or immunity to, a specific pathogen can form in two ways: exposure to the natural pathogen or exposure to an altered version of the pathogen in a vaccine.

Take-Home Message 26-5

• Antibodies are produced after exposure to an antigen. The specific immunity system is continually responding to numerous pathogens that can change over time.

26.6 Lymphocytes fight pathogens on two fronts

• Lymphocytes are the white blood cells responsible for the specific immunity response.

• These cells can be found circulating in the blood and lymphatic systems, and they reside in lymphatic organs such as the lymph nodes and spleen.

Antigen Receptors

Lymphocytes have antigen receptors, proteins on their plasma membranes that stick out from the cell surface and can bind to specificantigens—any one lymphocyte binding to just one type.

There Are Two Major Types of Lymphocytes

• B Cells and T Cells

• Both develop in the bone marrow.– T cells leave the

bone marrow and continue to mature in the thymus.

– B cells mature in the bone marrow.

Lymphocytes Fight Pathogens on Two Fronts

Humoral and cell-mediated immunity.

Humoral Immunity

• also referred to as antibody-mediated immunity

• protection against pathogens and toxins found in body fluids, such as blood and lymph

Cell-Mediated Immunity

• protection from pathogens located inside body cells

• carried out by T cells

Lymphocyte specificity

• Each lymphocyte has only one type of receptor that recognizes only one antigen, and it has many copies of this receptor on its surface.

• To defeat a specific pathogen, numerous identical lymphocytes (bearing the same antigen receptor) are needed.

Take-Home Message 26.6

• Two types of lymphocytes are associated with the specific immunity system: B cells and T cells.

• B cells are responsible for the humoral (antibody-mediated) response, and T cells for the cell-mediated response.

Take-Home Message 26.6

• Because of the diversity and specificity of lymphocyte receptors, almost any pathogen can be recognized by the body’s B and T cells.

26.7 Clonal selection helps in fighting infection now and later

When a lymphocyte does come into contact with the antigen specific to its receptor, a sequence of events begins—and it doesn’t end until the antigen is destroyed.

Clonal Selection• When a B or T cell binds to its

antigen, the cell and its descendants divide many times to create clones with the same antigen specificity.

• This process, known as clonal

selection, ensures that there are enough B and T cells to recognize and respond to a specific pathogen.

Recognize, Respond

and Remembe

r

Effector Cells

The responders, or effector cells, recognize an antigen and immediately take some action that leads to its destruction.

Plasma Cells

Plasma cells, derived from B cells, are the effector cells in the humoral response because they secrete antibodies.

Primary Response

• the immune system’s first interaction with a pathogen

Effector cells are not immediately available. Cells of the primary immune response must first be generated through clonal selection, which takes 2 weeks to produce effective numbers.

The Second Type of Lymphocytes

• produced through clonal selection, like effector cells

• remember antigens - if the body is infected with the same antigen in the future, it will be ready to attack

Secondary Response

• This is the creation of B and T effector cells.

• It occurs rapidly and produces a more intense response.

Take-Home Message 26.7

• When the body encounters a specific antigen, the lymphocytes recognizing this antigen divide to produce many cells through clonal selection.

Take-Home Message 26.7

• During a primary response, effector cells respond to and facilitate removal of the antigen.

• Memory cells produced during the primary response are ready to go through clonal selection if a secondary response is necessary.

26.8 The structure of antibodies reflects their

function• The diversity and

specificity of antibodies come from variations in a Y-shaped structure.

• Each antibody consists of four polypeptide chains joined together: two long (also called heavy) chains and two short (or light) chains

Variable Region

• The top of the “Y” is the region that varies from antibody to antibody.

• In the variable region, each antibody has a unique three-dimensional shape that dictates which specific antigen it will “fit.”

Constant Region

• There are only five variants for the lower part, the base of the “Y.”

• An enormous diversity of antibodies is needed to recognize a correspondingly enormous group of antigens that the immune system may encounter.

How Do Antibodies Work?

• They use the non-specific cells of the non-specific immune system (such as macrophages and neutrophils) to kill the pathogen.

• The antibodies act as beacons that make pathogens highly conspicuous to patrolling phagocytes.

Antibodies Act In Two Other Important Ways

1) They cause pathogens or antigens to clump together, making it easier for phagocytes to find and ingest them.

2) They coat the surfaces of pathogens and prevent them from binding to and entering body cells, thus blocking the infection from spreading.

Complement Proteins

• Antibodies indirectly lead to pathogen lysis through their recruitment of these complement proteins.

Passive ImmunityTransferring antibodies with a given specificity is termed passive immunity.– During pregnancy,

antibodies produced by the mother are transferred to the baby’s bloodstream and protect the baby for the first few months of life.

Take-Home Message 26.8

• Each antibody has a unique structure that recognizes a specific antigen.

• Plasma cells secrete high levels of antibodies into the blood and lymph.

Take-Home Message 26.8

• Antibodies are effective in helping to destroy pathogens and soluble antigens by enhancing ingestion by phagocytes, preventing more cell infection, and enhancing complement-driven lysis.

Take-Home Message 26.8

• Passive immunity is just short-term protection, because only antibodies are transferred, not the B cells that make the antibodies.

• What happens to all the body cells that already have viruses hiding inside them?

• It is the role of the T cell-mediated response to fight pathogens that are already inside cells.

26.9 Cytotoxic T cells and helper T cells serve different

functions.

There Are Two Major Types of T-Cells

1. Cytotoxic T cells - effectors of the cell mediated response; they directly kill cells infected with pathogens.

There are Two Major Types of T-Cells

2. Helper T cells - do not directly kill infected cells but, instead, stimulate other immune cells. – required in the stimulation of B cells to

produce antibodies and of cytotoxic T cells to kill infected cells

How Do Cytotoxic Effector Cells Fight the Internal

Pathogen?• They kill the

infected cell.• They use proteins

to destroy the cell membrane or promote apoptosis, or programmed cell death.

Take-Home Message 26.9

• Antibodies, produced by B cells, cannot destroy pathogens that are inside cells.

• The specialization of cytotoxic T cells is required to kill infected cells.

Take-Home Message 26.9

• Antigen-presenting cells display antigens to circulating helper T cells and cytotoxic T cells, to alert the specific immunity system to an infection.

• In turn, helper T cells produce cytokines that instruct cytotoxic T cells to mature and respond to the infection.

26.10 Autoimmune diseases occur when the body turns

against its own tissues

Autoimmunity occurs when an individual’s immune system responds inappropriately to the individual’s own cells and tissues as if they were pathogens, mistaking “self ” for “non-self.”

Autoantigens

Lymphocyte receptors wrongly recognize an individual’s own molecules or cellular structures as antigens, and the humoral and/or cell-mediated immune responses can be initiated by these autoantigens.

Multiple Sclerosis

In other disorders, the damage is spread throughout the body. – When the insulation

(myelin) that surrounds nerve fibers of the brain and spinal cord is under immune attack, the resulting disorder is called multiple sclerosis (MS).

Take-Home Message 26.10

• When lymphocytes bear receptors that inappropriately recognize structures of a person’s own body, autoimmunity develops.

Take-Home Message 26.10

• Autoimmune responses can do significant damage to specific organs or to tissues throughout the body, depending on where the antigens are located.

26.11 AIDS is an immune deficiency disease

• The human immunodeficiency virus (HIV), which causes AIDS (acquired immune deficiency syndrome), infects immune system cells, including helper T cells—cells that are crucial to survival.

• With AIDS, a deficiency of helper T cells leads to complete failure of the specific immunity response.

HIV/AIDS

• HIV infection occurs through contact with blood, semen, vaginal fluid, or breast milk from an infected person.

• Because individuals are contagious once they are infected, an initial lack of symptoms contributes to the spread of the disease.

HIV to AIDS*

• Occurs in three stages:– Acute phase• HIV infection

– Chronic phase• Person is infected, but not showing

symptoms

– Full-blown AIDS

Progression from HIV

infection to AIDS

HIV

• HIV is an RNA-containing virus that mutates rapidly.

• Even within a single host, the virus’s surface proteins can change with each new round of replication.

HIV Therapies

• Current therapies for HIV infection have been successful at increasing the length and quality of life for those infected.

• The regimen, called combination therapy, includes numerous drugs that affect HIV’s ability to replicate or infect new cells.

Resistance

• Drugs keep the virus number low and maintain a suitable number of helper T cells.

• HIV resistance to the drugs is a fear shared by both patients and clinicians.

Looking at a map depicting HIV/AIDS cases around the world, we can see just how widespread this virus is.

Take-Home Message 26.11

• AIDS is an immune system disease caused by the human immunodeficiency virus (HIV), which infects helper T cells—immune cells that are crucial to survival.

Take-Home Message 26.11

• As helper T cells are killed by the infection or by the body’s own cells in response to the infection, the deficiency of helper T cells leads to complete failure of the specific immunity response, resulting in illness and death from infections that a healthy immune system could defeat.

Take-Home Message 26.11

• There is currently no vaccine for HIV, because traditional vaccine methods do not work against this rapidly mutating virus, nor is there a cure for AIDS.

26.12 Allergies are an inappropriate immune response to a harmless

substance• The Centers for Disease Control and

Prevention (CDC) estimates that approximately 3 million children in the United States have food allergies.

• 90% are caused by just eight foods: peanuts, tree nuts, milk, eggs, fish, shellfish, soy, and wheat.

Allergies and Allergens

• Allergies are an inappropriate immune response to what should be a harmless substance.

• Allergens are antigens that causes an allergic response.

Allergens Introduce a

Humoral Response

Allergic Reactions

• Most allergic reactions occur in the digestive or respiratory tracts, because this is where the body first encounters an allergen that is eaten or inhaled.

Treatments

• Taking an antihistamine can alleviate some allergies, as these medicines block the inflammatory effects of histamine.

• Other medicines block mast cells from releasing histamine.

• Steroids block the production of cytokines from immune cells.

Anaphylactic Shock

• An individual with a severe allergic response may experience anaphylactic shock, a life-threatening allergic reaction that is systemic, meaning that it is not localized to the site of exposure.

Skin Allergy Testing

In this process, microscopic amounts of one or more potential allergens are injected under the skin.

Asthma is on the Rise

• Asthma results in an airway that is swollen and inflamed and leads to chest tightness, coughing, wheezing, and breathing difficulty.

• There are both genetic and environmental factors associated with asthma.

Take-Home Message 26.12

• In individuals who are sensitive, an allergen induces a humoral response in which one class of antibodies binds to and activates mast cells.

Take-Home Message 26.12

• A second exposure to the allergen leads to activated mast cells releasing histamine and cytokines, resulting in allergy-related symptoms.

• Swelling and inflammation can be localized or can be systemic and lead to anaphylactic shock.