ADAPTIVE IMMUNITYADAPTIVE IMMUNITY

*To adapt means to become suitable, *To adapt means to become suitable, and adaptive immunity can become and adaptive immunity can become “suitable” for and respond to almost “suitable” for and respond to almost any foreign antigen.any foreign antigen. *Adaptive immunity is: *Adaptive immunity is: -specific-specific-and is carried out by lymphocytes and -and is carried out by lymphocytes and macrophages.macrophages.*The majority of lymphocytes are *The majority of lymphocytes are -T cells -T cells andand -- B cellsB cells..

T CellsT Cells

In the embryo, In the embryo, T cellsT cells are produced are produced in the bone marrow and thymus.in the bone marrow and thymus.

They must pass through the thymus, They must pass through the thymus, where the thymic hormones bring where the thymic hormones bring about their maturation. about their maturation.

The T cells then migrate to the The T cells then migrate to the spleen, lymph nodes, and lymph spleen, lymph nodes, and lymph nodules, where they are found after nodules, where they are found after birth.birth.

B CellsB Cells

Produced in the embryonic bone Produced in the embryonic bone marrow, then migrate directly to the marrow, then migrate directly to the spleen and lymph nodes and nodules. spleen and lymph nodes and nodules.

* When activated some B cells will * When activated some B cells will divide many times and become divide many times and become plasma cells that produce antibodies plasma cells that produce antibodies to a specific antigen.to a specific antigen.

*The mechanisms of immunity that *The mechanisms of immunity that involve T cells and B cells involve T cells and B cells are specificare specific

macrophagemacrophage

. A macrophage has receptor sites . A macrophage has receptor sites for foreign chemicals such as for foreign chemicals such as those of bacterial cell walls or those of bacterial cell walls or flagella, and may phagocytize just flagella, and may phagocytize just about any foreign material it about any foreign material it comes acrosscomes across

steps of destruction of a pathogensteps of destruction of a pathogen

1- recognition of its antigens as foreign.1- recognition of its antigens as foreign. The foreign antigen is first phagocytized by a The foreign antigen is first phagocytized by a

macrophagemacrophage, and parts of it are “presented” on , and parts of it are “presented” on the macrophage’s cell membrane. the macrophage’s cell membrane.

If a specialized group of T lymphocytes ( called If a specialized group of T lymphocytes ( called helper T cellshelper T cells ) )encounters this macrophage, it encounters this macrophage, it become sensitized to that antigen and initiates become sensitized to that antigen and initiates both mechanisms of adaptive immunityboth mechanisms of adaptive immunity

Mechanisms of adaptive immunityMechanisms of adaptive immunity

1-1-cell-mediatedcell-mediated immunity immunity which involves:which involves:

--T cellsT cells

-and -and macrophages macrophages 2-2-antibody-mediated antibody-mediated immunity immunity (or (or

humoral immunityhumoral immunity), which involves:), which involves: - T cells,- T cells, - B cells,- B cells, -and macrophages-and macrophages

Cell-Mediated ImmunityCell-Mediated Immunity

No antibodies,No antibodies, effective against intracellular pathogens (such effective against intracellular pathogens (such

as viruses), fungi, malignant cells, and grafts of as viruses), fungi, malignant cells, and grafts of foreign tissue. foreign tissue.

After recognition of the foreign antigen by After recognition of the foreign antigen by macrophages and helper T cells, these activated macrophages and helper T cells, these activated T cells, which are antigen specific, divide many T cells, which are antigen specific, divide many times to formtimes to form

memory T cellsmemory T cells and and Cytotoxic Cytotoxic ( (killerkiller) ) T cells T cells

Cell-Mediated ImmunityCell-Mediated Immunity (cont.) (cont.) The The memory T cellsmemory T cells will remember the specific will remember the specific

foreign antigen and rapidly become active if it foreign antigen and rapidly become active if it enters the body again.enters the body again.

Cytotoxic T cellsCytotoxic T cells are able to : are able to : 1- chemically destroy foreign antigens by disrupting 1- chemically destroy foreign antigens by disrupting

cell membranes as destruction of cells infected with cell membranes as destruction of cells infected with viruses viruses

2- produce cytokines, which are chemicals that 2- produce cytokines, which are chemicals that attract macrophages to the area to phagocytize the attract macrophages to the area to phagocytize the foreign antigen and cellular debris.foreign antigen and cellular debris.

3-produce(with helper T) feedback chemicals to limit 3-produce(with helper T) feedback chemicals to limit the immune response once the foreign antigen has the immune response once the foreign antigen has been destroyed ( been destroyed ( T suppressorT suppressor). ).

Antibody-Mediated ImmunityAntibody-Mediated Immunity First step is recognition of the foreignFirst step is recognition of the foreign antigen, this time by antigen, this time by B cellsB cells as well as by as well as by macrophagesmacrophages and and helper Thelper T cells. cells. The sensitized helper T cell presents the foreign The sensitized helper T cell presents the foreign

antigen to B cells, which divide many times, and antigen to B cells, which divide many times, and two types of cells are formed:two types of cells are formed:

1- 1- memory B cellsmemory B cells, which will remember the , which will remember the specific antigen specific antigen

2-2-plasma cellplasma cell that produce antibodiesthat produce antibodies specific for this one foreign antigen.specific for this one foreign antigen.

AntibodiesAntibodies, , immune globulins immune globulins ((IgIg) or) orggamma globulinsamma globulins,,

*are proteins shaped somewhat like*are proteins shaped somewhat likethe letter Y.the letter Y.

* Antibodies do not themselves destroy foreign* Antibodies do not themselves destroy foreignantigens, but rather become attached to such antigensantigens, but rather become attached to such antigensto “label” them for destructionto “label” them for destruction. .

*Each antibody produced is specific for only one antigen *Each antibody produced is specific for only one antigen forming forming antigen antibodyantigen antibody complex labelled for complex labelled for phagocytosis or fixation by complementphagocytosis or fixation by complement

*millions of different antigen-specific antibodies can be *millions of different antigen-specific antibodies can be produced.produced.

CLASSES OF ANTIBODIESCLASSES OF ANTIBODIES

Cell-mediated

Antibody-mediated

Antibody Responses and Functions

1. On the first exposure to a foreign antigen, antibodies are produced slowly and in small amounts, and the person may develop clinical disease.

2. On the second exposure, the memory cells initiate rapid production of large amounts of antibodies, and a second case of the disease may be prevented.

This is the basis for the protection given by vaccines, which take the place of the first exposure.

3. Antibodies cause agglutination (clumping) of bacterial cells; clumped cells are easier for macrophages to phagocytize

4. Antibodies neutralize viruses by bonding to them and preventing their entry into cells.

5. Antibodies neutralize bacterial toxins by bonding to them and changing their shape so become not harmful and easily phagocytized

TYPES OF IMMUNITY

Genetic immunity is conferred by our DNA, and

acquired immunity is developed or

acquired by - natural or - artificial means.

Genetic immunity

Genetic immunity does not involve antibodies or the immune system; it is the result of our genetic makeup.

some pathogens cause disease in certain host species but not in others.

Dogs and cats, for example, have genetic immunity to the measles virus, which is a pathogen only for people

Acquired immunity

Acquired immunity does involve antibodies.

1-Passive immunity means that the antibodies are from another source,

2-active immunity means that the individual produces his or her own antibodies

naturally acquired passive immunity

1-placental transmission of antibodies (IgG) from maternal blood to fetal circulation. The baby will then be born temporarily immune to the diseases the mother is immune to.

2-breast-feeding, breast milk also contains maternal antibodies (IgA).

Artificially acquired passive immunity

is obtained-the injection of immune globulins (gamma globulins or preformed antibodies) after presumed exposure to a particular pathogen. Such immune globulins are available for German measles, hepatitis A and B ,tetanus and botulism (anti-toxins), and rabies-it is only for weeks or months

Active immunity Active immunity is the production of one’s own antibodies and may be stimulated by natural or

artificial means.

-Naturally acquired active immunity means that a person has recovered from a disease and

now has antibodies and memory cells specific for that pathogen.

-Artificially acquired active immunity is the result of a vaccine that has stimulated production of antibodies and memory cells

TYPES OF IMMUNITY

VACCINES

-

The purpose of vaccines is to prevent disease. A vaccine contains an antigen that the immune system will respond to, just as it would to the actual pathogen. - The types of vaccine antigens are a killed or weakened (attenuated) pathogen, part of a pathogen such as a bacterial capsule, or an inactivatedbacterial toxin called a toxoid

allergy

An allergy is a hypersensitivity to a particular foreign antigen, called an allergen.

-Allergens include plant pollens, foods, chemicals in cosmetics, antibiotics such as penicillin, dust, and mold spores.

-Such allergens are themselves harmless as most people, for example, can inhale pollen, eat peanuts, or take penicillin with no ill effects.

AGING AND THELYMPHATIC SYSTEM

Elderly people are more likely than younger ones to develop:

-infections as influenza and to what

are called secondary infections, such as pneumonia

-Autoimmune disorders as rheumatoid arthritis

-cancer is also higher