Immune System

The Immune System is a complex set of cells, molecules, and tissues that allow for biological processes that protect and fight the host organism from invading foreign objects, rogue cells in the body, cancer cells, and other potentially harmful particles.

Several foreign objects such as virus, bacteria, parasites, and other objects can damage the body

Some things within the body itself will attack such as cancer and autoimmune disease

Overall the immune system has a large and challenging task of protection, detection, modification, and destruction of the above-mentioned issues and several more.

Organs involved in the Immune System


–  This organ probably has a large effect in control and message sending of the immune system
–  Stressors can cause reactions from the brain
–  Microglia cells are glial cells in the brain that can cause an inflammatory response and can activate a T-cell response


–  Cilia are tiny hair-like structures that protect the Respiratory System from foreign articles
–  Breathing is a large cause of foreign particles entering the system
–  Lung lining and protective cells are essential
–  Smoking can increase the chance of infection due to destruction of cilia and other bronchial tissues


–  Up to 20% of cells in the liver are immunological based cells
–  When compared to other cells – the liver has a larger amount of such cells
–  The first location of foreign articles from the GI tract coming in contact with the innate immune response
–  Kupffer cells are a type of Macrophages in the liver


–  Mesangial cells involved in the complement system


–  Without the spleen, you are at increased risk for infection
–  Although you can live without this organ
–  Synthesis of antibodies occurs in its white pulp
–  A very large reserve of cells for an immune response within the red pulp
–  Also stores a large number of Red blood cells

Lymph Nodes

–  A broad spectrum of organs
–  Several different cell types
–  Contain white blood cells to fight infection
–  Act like filters of the lymph system
–  Antibodies can be produced in these organs
–  Are found throughout the body


–  Contains plasma, red blood cells, white blood cells, platelets
–  Proteins, antigens, antibodies are transported
–  Foreign particles can be transported as well
–  Initiating factors for inflammation response

Bone Marrow

–  Most of the White Blood cells arise in the bone marrow
–  Hematopoiesis occurs which is the process of the formation of blood cellular components


–  Synovial A cells
–  Involved in some inflammatory conditions such as Rheumatoid Arthritis


1st line Defense

–  A good defense will protect the body from the majority of diseases and attacks on the body
–  Skin  –  a physical barrier that protects from entering the organism
–  Coughing  –  protects openings such as lungs and respiratory system
–  Sneezing  –  protects the opening of the nasal mucosa, esophagus, lungs, and respiratory system
–  Mucus  –  protects the gastrointestinal tract or digestive system
–  Tears  –  protects the eyes
–  Vaginal Secretions  – A chemical barrier
–  Acids in the stomach –  protects the digestive region
–  Good bacteria  [Commensal flora]  –  protects against serious bacteria in the digestive system
–  Other chemical defense

Inner body defense

Innate Immune System

–  Cellular defense
–  Starts by “pattern recognition receptors
–  Designed to recognize a “friendly” or “foe” – then cause a response to the “foe”
–  This also helps when a normal cell becomes damaged and begins a process of breakdown

1.)  Humoral and chemical barriers



–  This is a process that tells the surrounding tissue that something is going wrong.
–  Can be a response to damage or an immune process
–  An increase of blood flows to the particular area is observed

Symptoms of inflammation

–  Swelling
–  Redness
–  Pain
–  Increased blood flow to the area

Types of chemical molecules involved in immunity

–  Cytokines
–  Chemokine  [promote chemotaxis]
–  Eicosanoids
–  Interferons  [viral protection]
–  Leukotrines  [can attract leukocytes or white blood cells]
–  Prostaglandins  [can cause fever and increased size of blood vessels]
–  many others

2.)  Complement System

–  This is a complicated system that is involved in the immune system of an organism
–  Several different components are involved in this system.
–  This system is a cascade system that begins with a certain biochemical process that causes several subsequent reactions.
–  This system causes a foreign object to be identified as foreign and destroyed.

3.) Cellular barriers

–  Major player involved in this system is Leukocytes
–  Is an aspect of the “adaptive immune system.”
–  Leukocytes are also referred to as white blood cells.


Leukocytes can be divided into the following cells

–  Macrophages
–  Neutrophils
–  Dendrite cells
–  Mast Cells
–  Basophils
–  Eosinophils
–  Natural killer cells

*** These cells find and identify foreign objects in the body.


–  An important responsibility of cellular response.
–  Main players are Macrophages and Neutrophils
–  The action of these cells is to overtake and engulf foreign objects and other particles.
–  It is as if these particles “eat” and destroy these objects.
–  Following the overtaking of the object – the cells transform into a phagosome.
–  The phagosome is then combined with a cellular component called the lysosome.
–  Digestive enzymes cause the phagosome to become destroyed.

Adaptive Immune System

–  This system is designed to be less random as Innate immune system which attacks almost anything that is considered foreign or non-self.
–  In the adaptive system, a pathogen is identified and a memory is made of that pathogen.
–  A signature antigen is produced to a “non-self” – this is referred to as antigen presentation



–  These are a special group of leukocytes.
–  These cells arise from stem cells in the bone marrow.

Types of cells are:

1.)  B cells
2.)  T cells

B Cells

–  Also referred to as B lymphocyte
–  This type of cell allows for a humoral immune response
–  This response has involved antibodies and antigens
–  Antibodies bind to antigens on surfaces of invading microbes  (viruses and bacteria for example)
–  This “tags” the molecule which then allows them to be found and destroyed
–  B cells themselves, a primarily tasked to make the antibodies
–  A small number, following an infection or attack, will divide and become memory cells
–  These cells allow the memory of the infection and allow a preparedness for a potential future attack

T Cells

–  This type of cell allows for cell-mediated immunity
–  This type of cell is not involved with antibodies or complement
–  Activation of other cells is essential
–  Macrophages, natural killer cells, and release of cytokines are part of this system
–  T stands for thymus
–  Several functions of this cell exist
–  Helper T cells, Cytotoxic T cells, and others help prevent and destroy infected cells, cancer cells, and more.


Immune Memory

–  As the first attack finishes and the immune response has been fulfilled.
–  Certain Active Cells will help the body of the organism remember certain aspects of the attack.

For B cells

–  Certain memory B cells are formed from active B cells.
–  These cells will live for long periods of time
–  When a second exposure to a specific antigen occurs – these cells are ready
–  Antibody production to specific antigen can be quicker

For T cells

–  Certain memory T cells will remain long after an infection
–  Once a second exposure occurs then these cells will reproduce quickly
–  Two main types:  1.) Central memory Cells and 2.) Effector memory cells

Passive Memory

–  This type of memory occurs in newborns who have never been exposed to microbes and infections
–  The action of this system is borrowing antibodies but not producing the antibodies themselves
–  This will leave them very vulnerable to infection without outside help
–  Outside help comes from the mother
–  Antibody IgG is transported from mother to fetus prior to birth through the placenta
–  This allows the baby to have antibodies at the time of birth
–  Breast Milk or colostrum also contains antibodies that are transferred to the infant
–  Therefore this type of immunity is short-lived and may last a few days following birth to a few months

Destruction of Tumors

–  This is an important aspect of the immune system
–  Tumors often occur when normal cells become abnormal and overabundant
–  They release and express antigens that are abnormal when compared to normal cells of the same type
–  Some antigens come from viruses such as the human papillomavirus involved in cervical cancer
–  Enzymes may produce antigens and several other causes for abnormal antigen release
–  The immune response is often swift and efficient
–  Killer T cells and other specialized cells help fight against these cells
–  Some tumor cells evade detection of this system and go on to become a cancer
–  When cancers evade detection, immune response can be less effective or more difficult
–  Medications, chemotherapy, and radiation may be used to achieve a type of immune response.

Disorders of Human Immunity

–  The goal for the immune system is efficiency, specificity, control, adaptation, and ability
–  When the goal fails and failure of the defense system occurs
–  This failure can be divided into 3 main categories

1.)   Hypersensitivities
2.)   Immunodeficiencies
3.)   Autoimmunity


–  This an immune response that damages the host’s own cells and tissue.
–  Divided into 4 classes:   I, II, III, IV
–  Each class typically is a different action or causation
–  Type I  –  Associated with allergy –  anaphylactic reaction
.     Symptoms from discomfort to death
–  Type II –   Associated with antibodies from cells of the host rather than from a foreign invader
–  Type III   –   Associated with Immune Complex of antigens that trigger this type of response
–  Type IV   –   Associated with autoimmune and infectious disease


–  One or more aspects of the immune system become unresponsive and inactive
–  Immune system is less effective in adults and very young children
–  Other conditions can worsen the effects of the immune system including cancer, AIDS, Malnutrition, Obesity, Diabetes, and several other conditions.
–  Lack of vitamins and Iron can hurt immune response
–  Genetics may predispose an increased difficulty with immune response


–  This causes an overactive immune response
–  Dysfunction of the immune system can be severe
–  The immune system fails to determine the difference between “self” and “non-self“.
–  Part of the body, tissue, or cells can be attacked

History of Immunology

–  This science is vast and expansive
–  The earliest mention of immunity was in 430 BC by Thucydides who noticed that a plague in Athens who noticed that when someone recovered from the plague, they could then assist those recovering and had little concern of becoming affected again.
–  Louis Pasteur development of vaccine understand with the “germ theory of disease”
–  1891 – Robert Koch’s proofs that confirmed microbes can cause certain infections
–  1901 –  Walter Reed discovered the yellow virus
–  Additional understanding in immune has continued over the past century