The Immune System

ATS Unit 7

Learning Goals

• Discuss the functions of the immunes system. • Differentiate between mechanisms of specific

and nonspecific immunity. • Identify functions of various immune cells and

proteins. • Immune cells are produced by the bodies

lymphatic tissues.

Thoughts on Immunology

• This science is very new. – We are still earning the complexities of how

immune cells form, interact, and change throughout life.

– This stuff can be confusing. We will take it one step at a time. We will start simple and build up.

Functions of the Immune System

• The immune systems’ job is to protect the body against disease and damage from pathogens. – This includes microbial pathogens, allergens, toxic

chemicals, and malignant cells (cancer). – Functions are broken down into specific and

nonspecific defense. – Further broken down into cellular and humoral

immunity.

Specific vs. Nonspecific Immunity

Nonspecific• Does not require any

adaptation. • We are born with these

responses. • The defenses are general

(they can attack lots of different antigens).

• Act immediately, do not require time to develop.

Specific• We “learn” these defenses

via exposure to antigens. • The defenses are meant for

only one antigen. • Takes time to build up in

system, and may decrease over time with no repeat exposure.

THE NON SPECIFIC IMMUNE DEFENSES

Key Points

• NONSPECIFIC defenses are defenses that are general (not aimed at specific factors). – This includes defense in the skin, mucous

membranes, respiratory, digestive, urinary and reproductive tracts to prevent disease.

– Also include the inflammatory response and nonspecific cells that attack antigens.

The Innate Response System

• The nonspecific defenses are known as this because they do not take any adaptations or “learning” to act.

• Can respond to antigens without knowing what exactly they are.

• Two “lines” of Defense

1st Line Defense

• These are our Barriers which are always active. – Skin– Chemical Barriers (stomach acid, skin oil, mucous

in respiratory system, urinary tract, digestive system, etc.

– Sneezing, coughing

2nd Lines of Defense

• Two parts: – Inflammatory Response (the “battlefield”)• An nonspecific response to injury or antigen. • Causes a tissue response, brings in reinforcements to

deal with antigens. – Phagocytes• Cells that “eat” antigens – recognizes lots of different

types of foreign particles and organisms. • Basically attacks anything they can identify as shady or

out of place.

Inflammatory Response

• This is mediated by both special immune cells located in the tissues, and by elements in the blood.

• Inflammation is a natural response to injury and/or irritation.

• Regulated by: – Certain types of white blood cells– Chemicals such as histamines

Inflammatory Response

Signs• Redness near the injury• Swelling (edema) via

vasodilation and increased permeability.

• Increased blood flow• Increased presence of

immune cells. • Pain

Functions• The increased circulation

allows the important protective cells to reach the site of injury.

• Swelling and pain help to protect the injury.

Inflammatory Response

Special Cells in the Nonspecific Defenses

• Phagocytes – “eat” or destroy pathogens and dead cells– Macrophages move in and out of the blood stream to eat up

harmful cells. – Neutrophils dump chemicals onto harmful cells to dissolve

them. • Basophils and Eosinophils – release chemicals called

histamines and other toxins to destroy pathogens (can also harm body’s own tissue).

• Natural Killer Cells – kill body’s cells that have been compromised, whether by mutation or by viral infection.

SPECIFIC IMMUNITY

Key Points

• Again, these types od defenses must be “learned” throughout life.

• They respond to “specific” antigens. • Body develops memory after initial exposure

to react in future encounters.

Immunoglobulin (Antibodies)

• There are 5 types: IgG, IgA, IgM, IgD, IgE• Each responds to a different type of antigen. • These do not kill microbes or remove them,

they just mark them. • IgG is the most abundant, is found in blood and

lymph and is active against most microbes. • IgE is active in response to allergens. .

Antigen-Antibody Reactions

• Antigens are proteins that attach themselves to antigens.

• By doing so, they may mark the pathogen for disposal, or just prevent it from binding with other body cells.

Cells of Specific Immunity

• These are produced in Lymphatic Tissue (more on that later). – Most functions are regulated by two types of cells. • B Lymphocytes• T Lymphocytes (Helper, Killer, and Suppressor)

– Other cells include macrophages and plasma cells that are activated by action in the B and T cells.

First Steps Toward Adaptive Immunity

• Initially, triggered by a response from the nonspecific system, which initially marks the antigen as “foreign and dangerous”: – Nonspecific responses, such as phagocytes, attack

and kill antigens. – In the meantime, Helper T Lymphocytes release

chemicals to stimulate the formation of specific antibodies.

Lymphocyte Action

T Lymphocytes• T for Thymus• Stimulates creation of:

– Killer T Cells – kill marked pathogens.

– Memory T Cells – hang out in the body, ready to recognize the infection again.

B Lymphocytes• B for Bone Marrow• Stimulates the creation of:

– Plasma Cells – secrete antibodies against the specific antigen. (remember antibodies mark the antigen for destroying)

– Memory B Cells - hang out in the body, ready to recognize the infection again.

Subsequent Encounters with Known Pathogens

• Initial immunity takes several days to develop (why we get sick)

• After that, the T and B lymphocytes that serve as memory cells quickly respond and create lots of antibodies and killer T cells to get rid of the antigen.

Acquiring Immunity

Active• Our bodies go though the

whole process of lymphocyte stimulation, antibody production, etc.

• It is typically long lasting. • We get in naturally from

actual illness/infection. • We can get it artificially via

vaccines.

Passive• Immunity we borrow from others. • Our bodies do not develop

memory cells in this situation. • We only get the antibodies to

fight the present infection. • We get this naturally via our

mother’s placental blood before birth and breast milk in infancy.

• We get this passively via injected antitoxins or immunoglobulin infusions.

Autoimmunity

• Sometimes, mechanisms in the body can become confused and attack cells that are not foreign or pathogenic. – We call the autoimmunity. Diseases in this class

include lupus, Type 1 diabetes, Crohn’s Disease, MS and many more.

– It may cause the body to attack one type of tissue or several.

– Treatments focus on decreasing the body’s immune response.

Hypersensitivity

• Sometimes, the immune system over-reacts to a substance that is not harmful or disease causing. Commonly, we call this an allergy. – Antibodies are made in large quantities against non-

harmful substances. – Can create local or systemic immune responses including

the inflammatory response, up to a anaphylaxis. – Common allergies include plant pollen, animal dander, and

foods such as peanuts. – We can treat these reaction with medications that block

histamines and other elements of the immune system.

LYMPHATIC SYSTEM

The Lymphatic System

• Series of vessels and nodes throughout the body.

• Functions: – Return fluids to the circulatory system that have

escaped. – Filters fluid for waste and monitors for pathogens. – Helps with absorption of fats/fat soluble vitamins. – Creates Lymphocytes in response to disease.

(Specific immunity)

Lymph Vessels

• These run along the same pathways as the circulatory system. – Fluids in these vessels more very slowly. – Vessles have valves. – Fluid in vessels is called lymph. – Along the lines of lymph vessels, there are lymph

nodes.

Lymph Nodes

• These are oval shapes structures located all through out the body, and especially near the roots of the limbs and in the neck. – If infection is present in the fluid that is filtered in

the node, the immune response begins. – Lymph nodes contain macrophages and create

lymphcytes with help fight disease. – If they become overwhelmed with pathogens,

they will become inflamed.

Tonsils

• Tonsils are like open lymph nodes. – They serve as gate keepers in the respiratory and

digestive tracts. – They catch pathogens and hold them so that they

can be attacked by immune cells. – Research shows that people who have their tonsils

removed due to issues in early life have higher rates of respiratory illness later in life.

Other Lymph Structures

• The Spleen: – Helps to recycle and store red blood cells, as well

as serves to filter blood and make monocytes and lymphocytes,

• Thymus: – Coverts immature lymphocytes to killer T Cells– Most active in early life when immune system is

still developing.