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Immune System

Protects from bacterial and viral pathogens, toxins, even cancerous cells


Immunity in Cellular Slime Molds

Composed of many individual amoeboid cells living in unison as a “slug”
Sentinel cells – circulate throughout the slug and engulf bacteria and toxins
Eventually remove themselves from the body of the slug


Immunity in Drosophila

Contain cellular receptors capable of recognizing common components of pathogenic microbes
Pathogen-associated molecular patterns (PAMPs)
Trigger an immune reaction
Receptors for PAMPs found in diverse organisms.
May have been one of earliest cellular receptors that evolved for pathogen recognition


innate immunity!

-Recognizes microbial invaders quickly, but shows no signs of an increased response upon repeated exposure
Both Immunity in Drosophila & Immunity in Cellular Slime Molds illustrate a type of defense


Adaptive immunity

Results in the production of receptors on surface of white blood cells that bind to a foreign antigen
Stimulates lymphocytes to increase in number, resulting in an increased response to specific antigens and immunological memory
Originally developed in an ancestor that gave rise to the jawed vertebrates
Precise mechanism causing adaptive immunity in ancestor not known



The capability of removing or killing foreign substances, pathogens, and cancer cells from the body.


Innate Defenses

Do not distinguish one type of threat from another
Are fully functional without previous exposure to invaders
Occur immediately or shortly after infection occurs


Types of innate immune defenses!

Physical and chemical barriers to entry
Inflammatory response
Phagocytes and natural killer cells
Protective proteins such as complement and interferons


Physical and Chemical Barriers

Skin and mucous membranes lining the respiratory, digestive, and urinary tracts
Cilia lining the respiratory tract sweep mucus and particles into the throat
Antimicrobial molecules in secretions of oil glands, mucous membranes, and the stomach


Examples of Antimicrobial molecules

Lysozyme, in mucus, an enzyme that lyses bacteria
Acidic pH of stomach kills microbes


Inflammatory Response

Localized tissue response to injury
Damaged cells and mast cells release histamine which causes capillaries to dilate and become more permeable.
Enlarged capillaries cause skin to redden.
Swelling stimulates free nerve endings, causing pain.
Neutrophils and monocytes migrate to the site of injury.


How do monocytes and neutrophils work in inflammatory response.

Monocytes differentiate into macrophages.
Macrophages release colony-stimulating factors, stimulating production and release of white blood cells.
Neutrophils, dendritic cells, and macrophages phagocytose pathogens



Maintenance of an elevated body temperature
In some instances, a fever may be beneficial.
It’s the body’s way of informing us that something is wrong.
Certain bacteria or viruses may not survive as well at higher temperatures.
Some immune mechanisms work better at higher body temperatures.



Leave the bloodstream and phagocytize bacteria
Release antimicrobial peptides and bacteria-digesting enzymes
Generate free radicals which kill engulfed bacteria



Phagocytic cells
Also mount an attack against parasites that are too large to be consumed via phagocytosis


Macrophages and dendritic cells

Engulf and destroy pathogens
Stimulate T cells in lymph nodes, which initiate adaptive immune responses


Natural killer (NK) cells

Large, granular lymphocytes
Kill virus-infected cells and cancer cells by cell-to-cell contact
Virus-infected cells, lacking a self molecule (MHC-1) may be recognized and killed.
Numbers don’t increase after stimulation, like lymphocytes.



A collection of plasma proteins that “complement” certain immune responses
Must be activated by pathogens


complements help destroy pathogens in three ways

Enhanced inflammation
Bind to pathogens coated with antibodies to ensure phagocytosis
Form a membrane attack complex that produces holes in the surface of some bacteria and viruses
--Fluids entering bacterial cell or virus cause bursting



Cytokines that affect the behavior of other cells
Produced by virus-infected cells
Bind to receptors of non-infected cells
Causes them to produce substances that interfere with viral replication
Used to treat certain cancers and viral infections, such as hepatitis C


Adaptive Immune Defenses

Also known as acquired immunity
Because adaptive defenses are not inborn
Take 5–7 days to become activated but last for years
Involve three steps


3 steps of adaptive immune defense!

Recognition of an antigen
Response to the antigen
Memory of the antigen



An antigen is any substance that stimulates the immune system to react.



Are capable of “recognizing” and binding to specific antigens
Have antigen receptors on their plasma membrane
The receptor protein’s shape allows it to combine with a specific antigen.
Pathogens, cancer cells, and transplanted tissues and organs bear antigens the immune system recognizes as nonself.


Adaptive immunity is primarily the result of

B cells and T cells


B cells

B-cell receptors bind directly to antigens.
B cells give rise to plasma cells.
Plasma cells produce and secrete antibodies.


T cells

T-cell receptors bind to antigens presented by antigen-presenting cells.
Helper T cells regulate specific immunity.
Cytotoxic T cells kill virus-infected cells and cancer cells.


Clonal selection theory

The antigen selects which lymphocyte will
Undergo clonal expansion
Produce more lymphocytes
Most of the cloned lymphocytes become plasma cells that produce specific antibodies.
Some of the cloned lymphocytes become memory B cells.
If the same antigen enters the system again, memory B cells quickly divide and give rise to more lymphocytes capable of quickly producing antibodies.


Antibodies (immunoglobulins)

Consist of two heavy and two light polypeptide chains in a Y shape
Both types of chains have variable and constant regions.
Neutralize pathogens by coating their antigens, preventing them from binding to receptors on cells
Attract white blood cells that move in for the kill
Immune complexes may be engulfed by neutrophils or macrophages or may activate the complement system.


Class is determined by the structure of the antibody’s constant region.!

IgG – Main type of antibody in circulation!
IgA – Main type secreted in milk, tears, and saliva
IgM – The first antibodies produced; also indicate infection
IgE – Bound to receptors on eosinophils and mast cells in tissues


Monoclonal Antibodies

Antibodies against a specific antigen
All of the same type
In vitro (outside the body in the laboratory) production of monoclonal antibodies
B cells are removed from an animal and exposed to a particular antigen.
The resulting plasma cells are fused with myeloma cells (malignant plasma cells that live and divide indefinitely).
The fused cells (hybridomas) secrete the monoclonal antibody


Medical Uses for Monoclonal Antibodies

To make quick and certain diagnoses of various conditions
Used to signify pregnancy by detecting a particular hormone (hCG) in the urine of a pregnant woman
Promise as potential drugs to help fight disease



a common virus that causes serious respiratory tract infections in very young children, is being treated with a monoclonal antibody drug.
Since the first therapeutic monoclonal antibody was approved by the FDA in 1986, over 20 are now available and hundreds more are being tested.


Adalimumab (Humira)!

binds to and inhibits tumor necrosis factor and is used to treat several autoimmune diseases.


T-Cells and Cell-Mediated Immunity

T-cells receptor (TCR) recognizes antigens displayed by antigen-presenting cells (APCs).
Antigen is first linked to a major histocompatibility complex (MHC) protein in the plasma membrane of the APC.
After the TCR binds to the antigen, the T cell undergoes clonal expansion.
After the immune response has been successful, most of the T cells undergo apoptosis.
Some T cells remain as memory T cells.


Cytotoxic T Cells

Destroy antigen-bearing cells
Contain storage vacuoles containing perforins and granzymes


Helper T Cells

Activate other T cells and B cells
Regulate immunity by secreting cytokines (signaling molecules)


Memory T cells

Persist after a successful immune response
Provide protection if the same antigen is encountered again


HIV Infections

The primary host for HIV is a helper T cell.
The host (helper T cell) produces viruses that go on to destroy more helper T cells.
At first an individual is able to stay ahead of the virus by producing enough helper T cells.
Gradually, the HIV count rises and the helper T-cell count drops.
Affected patients become susceptible to opportunistic infections.
Characteristic of an AIDS diagnosis



-Soluble protein that acts as a signaling molecule
-Cytokines called interleukins are produced by white blood cells.
--Stimulate other white blood cells
--Interleukins might awaken the immune system and lead to the destruction of the cancer.
---IL-2 is being used to treat some forms of melanoma and kidney cancer!!


Tumor necrosis factor (TNF) is a cytokine produced by macrophages (in cytokine)

Promotes the inflammatory response
Causes the death of cancer cells


Anti-TNF (in cytokine)

monoclonal antibodies are being developed as potential treatments for inflammatory diseases.


Active Immunity

It occurs when an individual produces his/her own immune response against an antigen.



It involves use of vaccines, substances that contain an antigen to which the immune system responds.
Pathogens or pathogen products treated to remove virulence are introduced to the patient via a vaccine.
It is dependent upon memory B cells and memory T cells capable of responding to lower doses of antigen


Passive Immunity

Occurs when an individual receives another person’s antibodies (immunoglobulins) or immune cells to combat a disease
Newborns are often passively immune since antibodies have crossed the placenta from the mother’s blood.
Breast-feeding prolongs natural, passive immunity.
– May be used to prevent illness in a patient who has
been exposed to certain infectious agents or toxins.
Examples: Rabies, tetanus, botulism, snake bites
– Cells of the immune system may be transferred to
a patient in the case of a bone marrow transplant.



They result in some degree of increased susceptibility to infection.
Primary immunodeficiencies are genetic, passed from parents to offspring.
Severe Combined Immune Deficiency (SCID)
Neither T nor B cells function
By about 3 months of age, when most of the antibodies an infant has obtained from the mother have been degraded, untreated SCID infants die.
Possible treatments include a bone marrow transplant.
X-Linked Agammaglobulinemia (XLA)
Caused by mutation in a gene on the X chromosome necessary for proper development of B cells



Hypersensitivities to substances that ordinarily would not harm the body


Immediate allergic response!

IgE antibodies!
Causes release of histamine, which brings about the symptoms of the allergy
Individuals with asthma have difficulty breathing and wheezing.
Anaphylactic shock – occurs after the allergen has entered the bloodstream.


Transplant Rejection

Antibodies and cytotoxic T cells cause destruction of transplanted foreign tissues in the body.
--Immune system is correctly distinguishing between self and nonself antigens.



It is the transplantation of animal tissues and organs into humans.
--Potential way to solve human donor organ shortage
--Genetic engineering makes animal organs less antigenic by removing MHC antigens.


Tissue Engineering

Production of human organs from stem cells may eliminate rejection problem.


Lymphatic System

Consists of lymphatic vessels and the lymphatic organs
Three main homeostatic functions:


Lymphatic System 3 main functions!

-Lymphatic capillaries take up and return excess fluid to the bloodstream.
-Lacteals absorb fats in the form of lipoproteins and transport them to the bloodstream.
-Lymphatic system produces, maintains, and distributes lymphocytes!!


Lymphocytes resist infection and disease by responding to

Invading pathogens such as bacteria or viruses
Abnormal body cells such as cancer cells
Foreign proteins such as toxins


Lymphatic Vessels

One-way system that begins with lymphatic capillaries
Tiny, closed-ended vessels found throughout the body
Take up excess tissue fluid (interstitial)
Lymph – fluid located within lymphatic capillaries
Lymph flows one way


Lymphoid (Lymphatic) Organs!

-Red Bone Marrow!
Site of origin for all types of blood cells
Site of maturation for B cells


Thymus Gland

Located between the trachea and the sternum in the upper thoracic cavity
Site of maturation for T cells
T cells migrate to thymus from red bone marrow.
T cells learn to recognize combinations of self and foreign molecules.
Mature T cells in bloodstream encounter foreign molecules or cells and proliferate and become activated.


Lymph Nodes

The capsule surrounds two distinct regions, cortex and medulla.
Macrophages concentrated in medulla cleanse lymph.
Macrophages “present” debris or pathogens to T cells in lymph node.
B and T cells in lymph nodes help destroy pathogens.
Lymph nodes are named for their location.



It is located in upper left side of the abdominal cavity just posterior to the stomach.
Macrophages remove old and defective blood cells.
Red pulp filters and cleanses blood.



Patches of lymphatic tissue are located in the pharynx.
They prevent entry of pathogens through the nose and mouth.


Peyer patches

Located in intestinal wall
Attached to cecum