THE HUMAN IMMUNE SYSTEM

FIRST LINE OF NONSPECIFIC DEFENSE

Pathogens are blocked from entering the body Skin Mucus membranes (release lysozyme) Cilia in respiratory system Stomach acid

SECOND LINE OF NONSPECIFIC DEFENSE

Inflammatory response Histamine triggers vasodilation, thus bringing

about more phagocytes

Secreted by basophils and mast cells in connective tissue

Histamine also causes sneezing, coughing, redness, itchy eyes and runny nose

SECOND LINE OF NONSPECIFIC DEFENSE

ProstaglandinsLipid compound promoting blood flow

ChemokinesAttract phagocytes to targeted area

PyrogensIncrease body temperatureSpeeds up immune systemDifficult for microbes to function

SECOND LINE OF NONSPECIFIC DEFENSE

Phagocytes ingest invading microbes Neutrophils engulf microbes and die within a

few days Monocytes transform into macrophages

(“giant eaters”) Use pseudopods to engulf large numbers of microbes

SECOND LINE OF NONSPECIFIC DEFENSE

Complement Group of 30 or more proteins that lyse or burst

invading cells

Interferons Block against cell-to-cell recognition of viruses

Natural killer cells Destroy virus-infected and cancer cells

SPECIFIC DEFENSE MECHANISMS

Third line of defense (specific) Uses B lymphocytes and T lymphocytes, both

made in the bone marrow Circulate in blood, lymph and lymphatic tissue

Spleen, lymph nodes and tonsils Both recognize specific antigens which cause the

production of antibodies

B LYMPHOCYTES

Fight disease in a humoral response (produce antibodies)

Each B lymphocyte secretes 2,000 antibodies per second over 4 -5 day life span

Become stimulated by T lymphocytes or viruses

T LYMPHOCYTES

Mature in thymus gland Fight pathogens through cell-mediated

response Stimulated by body cells that have been infected

with bacteria, viruses and parasites Cytoxic T cells and helper T cells are two

types of T lymphocytes

T LYMPHOCYTES

Cytoxic T (Tc) cells Kill body cells infected with viruses or other

pathogens and cancer cells Contain antigen receptors on their cell surface

that bind to protein fragments displayed by Class I Major Histocompatibility Complex molecules

When the Tc cell binds to this class I MHC molecule, a CD8 protein from the Tc cell holds to the two together until the Tc cell is activated

T LYMPHOCYTES

Once activated, the Tc cell differentiates into plasma and memory cells

These cells attack and kill cells by releasing perforin, a protein that forms pores in a cell’s membrane and causes the cell to burst

T LYMPHOCYTES

Helper T (Th) cells Announce to immune system that foreign

antigens are in the body Have receptors that bind to protein fragments

from Class II MHC molecules When a Th cell binds to a class II MHC molecule,a

CD4 protein holds the two cells together until the Th cell is activated

T LYMPHOCYTES

Th cells also differentiate into plasma and memory cells, like Tc cells

Th cells stimulate Tc cells by releasing the cytokines, which are interleukin-1 and interleukin-2

MAJOR HISTOCOMPATIBILITY COMPLEX MOLECULES

Also known as human leukocyte antigens (HLA)

They are cell surface markers that identify the cells as self

Class I MHC molecules are found on almost every body cell

Class II MHC molecules are found on specialized cells, like macrophages, B cells and activated T cells

CLONAL SELECTION

Helps develop immunity Antigenic molecules bind to specific B or T

lymphocytes Once a lymphocyte is selected, it clones

thousands of copies of itself in lymphatic tissue and differentiates into plasma cells and memory cells

CLONAL SELECTION

Plasma cells are short-lived Fight antigen immediately through primary immune

response (10 – 17 days) Memory cells are long lived cells bearing

receptors specific to the same antigen as the plasma cells Stay in blood in small numbers forever If body is attacked in the future by the same antigen,

memory cells rapidly reactivate

CLONAL SELECTION

This response is called the secondary immune response (takes 2 – 7 days)

This immunological memory is the mechanism that prevents you from getting any specific viral infection, like chicken pox, more than once

MACROPHAGES ACTIVATE HELPER T CELLS AND THE IMMUNE SYSTEM

Macrophages, (antigen-presenting cells) engulfs a bacterium and presents a fragment of it to the cell surface by an MHC II molecule

A specific Th cell is activated by binding to the MHC-antigen complex

Activated Th cell clones itself and secretes cytokines, which stimulate Th cells, B cells and Tc cells

ANTIBODIES

Also called immunoglobins Globular proteins shaped like the letter Y Consists of four constant regions (C) and four

variable regions (V) The tips of the Y have specific shapes and are

the binding sites for different antigens Five classes of immunoglobins are IgM, IgA, IgD,

IgE and IgG

ANTIBODIES

Destroy free-floating antigens Neutralize antigens by causing them to

clump, forming an antigen-antibody complex Complex is phagocytosed by macrophages

Also destroy antigens through complement fixation Activate a group of proteins to assist in lysing the

cell

ANTIBODIES

Made prior to exposure to antigenic agents When exposed to antigens, antibodies are

chosen by clonal selection from a limitless variety Many genes code for various regions Variety in antibodies is unlimited

PASSIVE IMMUNITY

Temporary Antibodies are transferred from another

person Pass through placenta to fetus or breast milk to

baby

ACTIVE IMMUNITY

Permanent Individual makes his or her own antibodies

after being ill or being given a vaccination Contains dead or weakened pathogens Stimulates a full immune response

BLOOD GROUPS AND TRANSFUSION

ABO antibodies circulate in the plasma and bind with ABO antigens in the event of an improper transfusion The danger in a transfusion is if the

recipient has antibodies to the donor’s antigens

Before a transfusion, a cross-match is done Two samples of donor and recipient blood are

mixed

BLOOD GROUPS AND TRANSFUSION

Blood Type Antigens Present on the Surface of the

Red Blood Cells

Antibodies Present

Circulating in the Plasma

A A B

B B A

O None A and B

AB A and B None

BLOOD GROUPS AND TRANSFUSION

Blood type O is the universal donor because it has no blood antigens to be clumped by the recipient’s blood

Blood type AB is known as the universal recipient because there are no antibodies to clump the donor’s blood

RH FACTOR

Another antigen located on the surface of red blood cells

85% of people have the antigen and are Rh+

15% are Rh-

AIDS

Acquired immune deficiency disease Highly susceptible to colds, infections and

cancers that thrive on collapsed immune systems

HIV (human immuno-deficiency virus) causes aids and attacks cells that bear CD4 molecules, mainly helper T cells

Retrovirus

POSITIVE FEEDBACK

Enhances already existing process Can be seen in helper T cells When a Th cell is activated, it releases

interleukin-I and interleukin-II IL-I enhances the activity of the already

activated Th cells, stimulating more of them until they are activated at a maximum

ALLERGIES

Hypersensitive immune responses to allergens

Involve the release of histamine, an anti-inflammatory agent

Involves redness, runny nose and itchy eyes Some acute allergic reactions can result in a

life-threatening response called anaphlyactic shock, which can result in immediate death (peanuts)

ANTIBIOTICS

Medicines that kill bacteria or fungi Administered after a person is sick Passive immunity

AUTOIMMUNE DISEASES

Multiple sclerosis, lupus, arthritis, juvenile diabetes

Caused by immune system mistake Cannot properly distinguish between self and

nonself With multiple sclerosis, the immune system

attacks the myelin sheath of neurons in the CNS

MONOCLONAL ANTIBODIES

Antibodies produced by a single B cell selected for a specific antigen

Important in research and in the treatment and diagnosis of diseases