ImmunityImmunity

Immunity is the Immunity is the protection against protection against disease provided by the disease provided by the bodybody’’s defence or s defence or immune system.immune system.

Immune ResponseImmune Response

not one single mechanism not one single mechanism Innate immunityInnate immunity, which does not require , which does not require

previous exposure to the invading previous exposure to the invading microbe, microbe,

Acquired immunityAcquired immunity, where the immune , where the immune system "remembers" how to deal with a system "remembers" how to deal with a microbe that it has dealt with before. microbe that it has dealt with before.

The key to a healthy immune system is its remarkable ability to distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “nonself.”

Antigen - a chemical feature (a a chemical feature (a protein) which is unique to any given protein) which is unique to any given type of invading organism. type of invading organism.

When it wrongly identifies self as nonself it causes an autoimmune disease such as rheumatoid arthritis or systemic lupus erythematosus.

PhagocytesPhagocytes

Produced by bone marrowProduced by bone marrow ScavengersScavengers Non-specificNon-specific Two types:Two types:

Neutrophils – small, short-livedNeutrophils – small, short-lived Macrophages – large, long-livedMacrophages – large, long-lived

Mode of actionMode of action

engulf pathogen and create enzymes to engulf pathogen and create enzymes to neutralize it neutralize it

This process is called This process is called phagocytosisphagocytosis, , literally "eating cells." literally "eating cells."

Macrophages use phagocytosis to collect Macrophages use phagocytosis to collect antigens which they present to helper T-antigens which they present to helper T-cells, alerting the T-cells to the fact that cells, alerting the T-cells to the fact that there is a foreign invader in the body, and there is a foreign invader in the body, and triggering an immune response. triggering an immune response.

LymphocytesLymphocytes

Made in bone marrow before birthMade in bone marrow before birth Stored in lymphoid systemStored in lymphoid system SpecificSpecific Secrete antibodiesSecrete antibodies Two groups:Two groups:

T lymphocytesT lymphocytes B lymphocytes B lymphocytes

T lymphocytesT lymphocytes Mature in thymus glandMature in thymus gland Specific surface receptors called Specific surface receptors called

T cell receptors and glycoprotein T cell receptors and glycoprotein receptors called CD receptors.receptors called CD receptors.

T CellsT Cells provide  provide Cell Mediated Cell Mediated ImmunityImmunity

T cells have several functions. They T cells have several functions. They can be:-can be:- Helper T cellsHelper T cells, which control other , which control other

cells, such as B cells or cells, such as B cells or Macrophages, directing them to Macrophages, directing them to carry out their task.carry out their task.

Suppressor T cellsSuppressor T cells, which dampen , which dampen down the immune response when it down the immune response when it is no longer needed.is no longer needed.

Cytotoxic T cellsCytotoxic T cells, which destroy , which destroy host cells that have become infected host cells that have become infected with the invading organism. (Killer T)with the invading organism. (Killer T)

B LymphocytesB Lymphocytes

Mature in bone marrowMature in bone marrow Each one has a specific receptor Each one has a specific receptor 10 million different variants10 million different variants These code for the different These code for the different

antibodiesantibodies

Mode of actionMode of action B CellsB Cells provide  provide "Humoral "Humoral

Immunity"Immunity".. Each B cell secretes a unique Each B cell secretes a unique

antibody, which acts against a antibody, which acts against a particular particular antigenantigen. .

When B cells meet an invading When B cells meet an invading organism for which they have the organism for which they have the antibody, they do one of two things.antibody, they do one of two things. They may turn into They may turn into antibody antibody

factoriesfactories and start manufacturing  and start manufacturing as many copies of their antibody as as many copies of their antibody as they can.they can.

They may clone themselves They may clone themselves increasing the numbers increasing the numbers of of antibody factoriesantibody factories, ,

Memory CellsMemory Cells

When B cells and T cells are activated When B cells and T cells are activated some will become some will become memory cellsmemory cells. .

Upon interaction with a previously Upon interaction with a previously encountered antigen, the appropriate encountered antigen, the appropriate memory cells are selected and activated. memory cells are selected and activated.

The second and subsequent exposures to The second and subsequent exposures to an antigen produce a stronger and faster an antigen produce a stronger and faster immune response. immune response.

AntibodiesAntibodies Each antibody consists of four Each antibody consists of four

polypeptides– two heavy chains and two polypeptides– two heavy chains and two light chains joined to form a "Y" shaped light chains joined to form a "Y" shaped molecule.molecule.

The amino acid sequence in the tips of the The amino acid sequence in the tips of the "Y" varies greatly among different "Y" varies greatly among different antibodies. antibodies.

This variable region, composed of 110-130 This variable region, composed of 110-130 amino acids, give the antibody its amino acids, give the antibody its specificity for binding to the antigen. specificity for binding to the antigen.

The constant region determines the The constant region determines the mechanism used to destroy the antigen. mechanism used to destroy the antigen. 

Active ImmunityActive Immunity

Naturally acquired active immunity occurs Naturally acquired active immunity occurs when the person is exposed to a live when the person is exposed to a live pathogen, develops the disease, and pathogen, develops the disease, and becomes immune as a result of the primary becomes immune as a result of the primary immune response.immune response.

Artificially acquired active immunity can be Artificially acquired active immunity can be induced by a vaccine, a substance that induced by a vaccine, a substance that contains the antigen. contains the antigen.

A vaccine stimulates a primary response A vaccine stimulates a primary response against the antigen without causing against the antigen without causing symptoms of the disease symptoms of the disease

Passive ImmunityPassive Immunity Passive memory is usually short-term, Passive memory is usually short-term,

lasting between a few days and several lasting between a few days and several months. months.

Newborn infants have had no prior Newborn infants have had no prior exposure to microbes and are particularly exposure to microbes and are particularly vulnerable to infection. At birth, human vulnerable to infection. At birth, human babies have high levels of antibodies, with babies have high levels of antibodies, with the same range of antigens as their mother. the same range of antigens as their mother.

This is passive immunity because the fetus This is passive immunity because the fetus does not actually make any memory cells does not actually make any memory cells or antibodies, it only borrows them. or antibodies, it only borrows them.

Short-term passive immunity can also be Short-term passive immunity can also be transferred artificially from one individual to transferred artificially from one individual to another via antibody-rich serum.another via antibody-rich serum.

VaccinationVaccination

Immunization or vaccination is the deliberate Immunization or vaccination is the deliberate induction of an immune response.induction of an immune response.

Immunizations are successful because they utilize Immunizations are successful because they utilize the immune system's natural specificity as well as the immune system's natural specificity as well as its inducibility.its inducibility.

An antigen, derived from a disease-causing An antigen, derived from a disease-causing organism, is injected and it stimulates the immune organism, is injected and it stimulates the immune system to develop protective immunity against that system to develop protective immunity against that organism, but the antigen does not organism, but the antigen does not itselfitself cause the  cause the pathogenic effects of that organism. pathogenic effects of that organism.

Most viral vaccines are based on Most viral vaccines are based on live attenuated viruses, while many bacterial live attenuated viruses, while many bacterial vaccines are based on avarious components of vaccines are based on avarious components of microorganisms, including microorganisms, including harmless chemical components.harmless chemical components.

Disease Eradication

Smallpox was eradicated in 1980 because:Virus did not mutate, so one vaccine always worked.Easy to identify infected peopleDoes not linger in the body to reinfect later.Vaccine could be freeze dried for use in the tropics (did not need to be refrigerated).

Other diseases are no so easy to readicate, such as…..

CholeraMalariaSickle-Cell anaemiaTBMeasles

Chart on page 232 explains why.

Monoclonal antibodiesMonoclonal antibodies

Identical antibodies produced to be effective Identical antibodies produced to be effective against a single, specific antigen.against a single, specific antigen.

Problem with producing them – B Problem with producing them – B lymphocytes that produce antibodies don’t lymphocytes that produce antibodies don’t divide, and B lymphocytes that divide divide, and B lymphocytes that divide (making plasma cells) don’t produce (making plasma cells) don’t produce antibodies!antibodies!

HAT medium is hypoxanthine aminopterin thymidine. Only hybridomas survive. Myeloma and normal cells die.

Plasma cells are fused with cancerous Plasma cells are fused with cancerous cells which go on dividing indefinitely.cells which go on dividing indefinitely.

This formed a hybridoma which divides This formed a hybridoma which divides and secretes antibodies.and secretes antibodies.

Using monoclonal AntibodiesUsing monoclonal Antibodies

1. Pregnancy Tests1. Pregnancy Tests The monoclonal antibodies are made that bind The monoclonal antibodies are made that bind

with the human hormone human chorionic with the human hormone human chorionic gonadotrophin (hCG), which is produced in gonadotrophin (hCG), which is produced in pregnancy.pregnancy.

The antibody is attached to a dipstick.The antibody is attached to a dipstick. The dipstick is dipped into a urine sample.The dipstick is dipped into a urine sample. Any hCG in the urine will bind to the antibody Any hCG in the urine will bind to the antibody

and will be carried up the stick with the urine.and will be carried up the stick with the urine.

Another antibody is made which will bind Another antibody is made which will bind with the hCG-antibody complex.with the hCG-antibody complex.

This is placed further up the stick and This is placed further up the stick and immobilised.immobilised.

As the hCG-antibody reaches the As the hCG-antibody reaches the immobilised antibody it binds and a pink immobilised antibody it binds and a pink colour forms. (or blue, depending on the colour forms. (or blue, depending on the brand)brand)

To check whether the stick is working, another chemical is attached to it that will change colour even if there is no hGC present.

One band: Negative, as there was no hCG.Two bands: Positive, as some of the mouse antibody has hCG bound to it.

Monoclonal antibodies in diagnosis Monoclonal antibodies in diagnosis and treatmentand treatment

Diagnosis.Diagnosis.

Blood clots:Fibrin (protein found in blood Blood clots:Fibrin (protein found in blood clots) injected into a mouse, and clots) injected into a mouse, and monoclonal antibodies against fibrin are monoclonal antibodies against fibrin are produced as previously discribed.produced as previously discribed.

The antibodies are labelled with a The antibodies are labelled with a radioactive chemical so that they can be radioactive chemical so that they can be traced.traced.

The monoclonal antibodies are then injected into the patient, and bind to the fibrin in their blood clots.

The radiation then shows the doctors where the blood clots are.

Cancer cells can be tracked down in a similar way to identify the location of a tumour.

Treatment:Monoclonal antibodies are made to be bind on to cancer cells. An anti-cancer drug is then joined to them.

These “magic-bullets” are then injected into a patient, and the anti-cancer drug is taken to the cancer cell by the monoclonal antibody, and the cancer cell is destroyed.