Chapter 42: The Immune System

Immunology

is the study of internal defense systems in animals (including animals)

Internal Defense

refers to self-generated protection from an agent that can cause harm to the organism

Immunity

is the ability to recognize and destroy foreign or dangerous pathogens

The immune system must be able to recognize …. as a result of cell-surface proteins that are different from one organism to the next (even among the same species)

self vs non-self

An animal’s immune system recognizes its own cells as… and can identify those of other organisms as…

1) host and 2) foreign

Immune systems can only be effective if…

they react to and destroy invaders (non-self), while not destroying its own cells (self)

Antigens

identification molecules found on cell surface

Non-self-antigens should …. the immune system

activate

Self antigens should …. the immune system

not activate

All of our nucleated cells have a receptor called….that can communicate with cells of the immune system

major histocompatibility complex (MHC)

Lymphatic vessels

consists of an extensive network of vessels that conduct lymph (a clear fluid formed from interstitial fluid)

Lymphatic tissue

Can be distinct organs (like the spleen, tonsils, adenoids, appendix, and thymus), small nodes (lymph nodes) along the lymphatic vessels, or simple aggregates of immune cells (like those found in the intestines)

Two Immune Systems

Innate Immune System and Acquired/Adaptive Immune System

Innate Immune System

1) Innate immune components found throughout all of the animal kingdom and even in the plant kingdom

2) Nonspecific- provides immediate, general protection against pathogens, parasites, some toxins and drugs, and cancer cells

3) No memory

Skin

(physical barrier) this is an anatomical, physical feature that prevents penetration of many hazardous agents

Acquired/Adaptive Immune System

1) Found only in vertebrate animals

2) Highly specific

3)Has memory (gives us the ability to recover from an infection and then have protection when exposed again to the same pathogen)

Physiological Factors

(physical barrier) pH (e.g. acidic stomach) and body temperature can inhibit the growth of some pathological microbial species

Mucous Membranes

(physical barrier) the mucous that lines body cavities contains chemicals (e.g. lysozyme) that can attack pathogens

Phagocytic Cells

(physiological mechanisms) toxic substances can be neutralized and pathogenic microbes can be digested by a variety of cells, including macrophages, monocytes, and neutrophils

Inflammation

(physiological mechanisms) localized accumulation of phagocytic cells and vasodilation can lead to swelling, redness, and fever in response to an infectious agent

Non-phagocytic cells

(physiological mechanisms) these cells release signals to stimulate other components of the immune system

Plasma proteins

(physiological mechanisms) most of these proteins are made by the liver or released by immune cells. They assist the function of immune cells and circulate in the plasma (non-cellular) component of the blood

Blood is composed of a watery component known as

plasma

By spinning a blood sample in a centrifuge, you can easily separate the … from the plasma

cellular components

Smaller components like nutrients, gases, hormones, proteins, and waste are…

in solution, so they do not stretch

Non-cellular components of the innate immune system…

circulate throughout the body in the plasma

Cellular components of the innate immune system…

also circulate in the bloodstream and separate into the buffy coat when blood is centrifuged

Cells involved in the innate immune system are…

leukocytes (WBCs)

Five types of leukocytes

basophils, eosinophils, neutrophils, monocytes, and lymphocytes

All but the lymphocytes are made in the…

bone marrow

Leukocytes travel in the…

blood stream and then slip through the walls of the blood vessels at the site of infection and enter the tissues

Their first separation is on the presence or absence of (leukocytes)…

cytoplasmic granules

Neutrophils

are phagocytic cells that ingest bacteria and dead cells

Eosinophils

contain lysosomes with enzymes that degrade cell membranes of parasitic worms

Basophils

release histamine in injured tissues and in allergic responses; and heparin, an anticoagulant

Monocytes

are phagocytes that migrate from blood into tissues during an infection

Macrophages

(monocytes) that engulf bacteria, dead cells, and debris

Dendritic cells

(monocytes) that are important in activating the immune system

Lymphocytes (B and T cells)

fight infections; some produce antibodies, others directly attack invaders such as bacteria or viruses

Lymphocytes (B and T cells) are apart of….

adaptive immune system

Microbes have different…

cell surface markers (antigens) than our cells that bind to receptors on leukocytes

Phagocytic cells recognize…

these pathogen associated molecular patterns (PAMPs) and phagocytize the cells

These markers are not specific…

they are found on wide range of microbes

Immune cells communicate with each other by releasing signaling proteins called…

cytokines

Cytokines bind to…

membrane receptors on target cells and initiate a response to the specific pathogen

Depending on the specific cytokine released…

cells will activate different cellular responses

Cytokines regulate…

immune responses, as well as cell growth, repair, and cell activation

Examples of Cytokines

interferon and interleukins

Interleukins

used to signal between different leukocytes

Interferon

released by virally infected cells to warn uninfected cells

The goal of the inflammatory response…

is to recruit more of the innate immune system to the site of an infection

Mast cells release histamine that causes…

vasodilation (increased blood flow)

This increased plasma in the tissue is called…

edema and is responsible for the tissue swelling at the site

Neutrophils and monocytes consume invading bacteria by…

phagocytosis, while other immune cells signal to stimulate the immune response

Fever

a common clinical symptom of widespread inflammation, helps the body fight infection

Elevated body temperature increases…

phagocytosis and interferes with the growth and replication of microorganisms

Complement

consists of proteins present in plasma and other body fluids that are non-specific

Complement examples

Lyse, Coat, Attract, Bind to specific receptors

Lyse

viruses, bacteria, and other cells

Coat

pathogens so macrophages and neutrophils phagocytose them more easily

Attract

leukocytes to the infection site (chemotaxis)

Bind to specific receptors

on cells of the immune system, stimulating specific actions, such as secreting regulatory molecules and enhancing the inflammatory response

Characteristics of Innate Immunity

1) Innate immune system recognizes PAMPs found on wide variety of microbes and thus can mount a robust response against a wide variety of pathogens

2) Organisms are born with a complete innate immune system and are thus prepared to combat pathogens immediately

Good characteristics of Innate Immunity

1) Is always present and ready to respond rapidly to invading pathogens

2) In many ways, this is the generic first line of defense.

Bad characteristics of Innate Immunity

1) repeated exposure to the same hazardous agent does not affect the speed or strength of protection

Adaptive immune system is found only in…

vertebrate organisms

Adaptive immune system…

it is highly specific – responding to antigens present on the surface of a single target pathogen

Lymphocytes carry out the…

main activities of the adaptive immune system

There are two major classes…

B lymphocytes (aka B cells) and T lymphocytes (aka T cells)

B and T Lymphocytes have specific cell surface receptors called…

B cell receptor (BCR) and T cell receptor (TCR) that can distinguish between antigens found on different pathogens

Antigen binding of these receptors initiates…

signaling cascades that activate the specific responses of the B cells and T cells

T cells…

Mature in the thymus before colonizing immune tissues throughout the body

3 major populations of T cells

Th – helper T cells, Tc – cytotoxic T cell, Treg regulatory cells

Th – helper T cells

(CD4+ cells) secrete cytokines and boost the function of other cells in the immune system

Tc – cytotoxic T cell

(CD8+ cells) attack cells that are infected with viruses, damaged, or cancerous

Treg regulatory cells

help limit the immune system to prevent overreaction

Why is it called cell-mediated…

because T cells must be in direct contact with target cells

Macrophages are known as… because

1) Antigen Presenting Cells (APCs) 2) because they take debris from engulfed pathogens and “present” them on their cell surface bound to the MHC class II receptor

Antigens bound to MHC II activate

T cells whose TCR recognizes the antigen being presented by the APC

Once bound to the MHC/antigen complex…

Helper T cells will then release cytokines to up regulate B cells and other immune cells

It will also go through mitosis…

to make clones of itself, including memory cells that can be used in subsequent infections

Cytotoxic T cells will…

kill infected self cells or altered (tumor) self cells

if this was the source of the antigen

For instance, if a cell is infected with a virus…

it will present some of that virus on its MHC Class I. The T c cell will then force that self cell to go through apoptosis

B Cells

Mature in the bone marrow before colonizing lymphoid tissues throughout the body

Each B cell has a…

different B cell receptor (BCR) that can recognize a different antigen via its variable region

When an antigen binds the BCR in the presence of interleukins

from helper T cells…

the B cell will start secreting high amounts of a non-membrane bound form of the BCR known as an antibody

Antibodies then (B-cells)

circulate freely in the bloodstream (one of the body humors/fluids)

The initial activation of a B cell clone will…

induce it to undergo many rounds of cell division to make copies of itself (clonal expansion)

Plasma cells

these cells produce large amounts of antibodies

Memory cells

these cells will be stored in the body to respond more quickly to a subsequent infection

Each B cell secretes….

antibodies with a specific variable region that recognizes a specific antigen (epitope)

Neutralization

blocking viral binding sites, coating bacteria

Agglutination

sticking multiple pathogens to each other

Precipitation

causing small molecules (toxins) to fall out of solution

Opsonization

binding of antibodies to a pathogen increases the probability that a macrophage will engulf it

On first exposure to a pathogen, it can take several days to weeks to…

mount a full adaptive immune response, during which time the body is dependent solely on the innate immune system

All aspects of the adaptive immune system store…

memory cells to create a faster, more robust response to subsequent exposures

Vaccines are a way to give a… so that the body

1) non-pathogenic exposure 2) goes through the primary response in the absence of a real pathogen

The memory cells made by the adaptive immune system during the

vaccination can…

then mount a more robust secondary response upon exposure to the actual pathogen

Adaptive immune response characteristics

Highly specific antibodies made by B cells and T-cell Receptors (TCRs) made by T cells in coordination with Major Histocompatibility Complexes (MHC)