UNIT IMMUNE RESPONSE:Specific and Nonspecific Body Defenses

The host-parasite relationship may result in an episode of disease.

In this case, the body will mount two general forms of defenses: nonspecific defenses and specific defense centered In the Immune system.

THE FATE OF INFECTING ORGANISMS: Several possible fates await organisms that

cause infections. This is a matter of practical interest, because

the transmission of the diseases to other individuals depends upon the escape of the organisms from theinfected one.

1. Some are destroyed by host tissue. Infections are not accomplished without resistance

on the part of the host because the host-parasite relationship Isn 't a natural one.

Fortunately, the capacity of hosts to destroy parasites is so great that the great majority of foreign living agents which manage to reachliving tissues and fluids, of the body are rapidly and completely destroyed...ongoing all time, (exception: Trypanosoma pg 302 add)

2. Some are eliminated in the secretion and excretion of the host. Elimination in this manner varies with the

disease. The longer the organism lasts, the more likely

the host is to eliminate large numbers of numbers of infected agents.

Elimination can be through: pus, abscess , bursts, droplet in cough or sneeze,

feces

3. If the disease proves fatal to host, many of the infecting organisms are destroyed with the body.

Death of the host form the infection always traps a large number of the infecting organisms.

4. In some instances the organisms and the host

reach an impasse, Where:

the organism is unable to cause serious damage to the host, and yet the host is unable to eliminate the organism...can occur throughout the organisms life span. Ex tuberculosis, typhoid fever

NONSPECIFIC MECHANISMS OF DEFENSE: The objectives of these mechanisms are to

prevent microorganisms from gaining a foothold in the body and to destroy them if they penetrate to the deeper tissues.

1. Mechanical barrier: first line of defense for the body, and are normally part of the body's anatomy and physiology.

a. skin: outermost layer of skin consist of compacted, cemented cellsimpregnated with the insoluble protein keratin

b. mucous membranes: line urinary, respiratory, and digestive tracts

c. nasal hairs: trap particles in the respiratory tract.

d. cilia: on the cells sweep and trap particles in respiratory tract, andcoughing ejects the material.

2. Chemical defenses The secretions and lubricating glands such

as the tears and saliva which contain the enzyme lysozyme (breaks down peptidoglycan cell wall of gram positive bacteria)

3. Genetic barrier: hereditary characteristics. Ex humans do not

suffer canine distemper because humans lack the appropriate receptor sites for the virus that causes the disease.

4. Inflammation: Nonspecific response to any trauma

occurring to tissues. Includes: heat, swelling, redness and pain. In some types of inflammation, phagocytes

accumulate in the whitish mass of cells,bacteria, and debris called pus

5. FEVER Is initiated by circulating substances called

pyrogens, which affect the brain's hypothalamus and cause the hypothalamus to raise the temperature. ..is believed to retard the growth of temperature sensitive microorganisms.

6. Phagocytes engulf and destroy the microorganism of

disease. Ex neutrophils and monocytes

7. Complement system a series of proteins that circulate in the

blood and encourage phagocytosis. Many immune reactions stimulate this

system to go into action.

SPECIFIC DEFENSES: (THE IMMUNE SYSTEM) Center around the immune system The immune system enables the body to

recognize a foreign agent as nonself, which is something other than a person's own substances (self).

The immune system takes a specific action for neutralizing, killing, and eliminating that agent.

These actions involve nonspecific resistance as well. On occasion, the immune system activity may lead to

tissue damage as seen in allergic disorders and hypersensitivities.

The system is based on its ability to distinguish characteristic proteins or protein-linked components associated with alien substances.

There are 2 main branches of the immune system:

1. . Antibody-mediated immunity (humoral immunity)

2. Cell-mediated immunity

ANTIBODY-MEDIATED (HUMORAL) IMMUNITY (AMI): Involves antibodies that are found in the blood

plasma and lymph. Antibodies are produced by B cells in response to a

specific antigen. Antibodies primarily defend as against bacteria,

viruses, and toxins in body fluids. On exposure to antigenic determinants in lymphatic

organs, B-lymphocytes are activated and differentiated to form plasma cells.

Plasma cells are specialized, differentiated cells that synthesize and secrete antibodies specific for an antigen.

CELL-MEDIATED IMMUNITY (CMI): Depends on T cells and does not involve

antibody production. Primarily a response to intracellular viruses,

multicellular parasites, transplanted tissue, and cancer cells.

ANTIGENS AND ANTIBODIES: Antigen: a chemical substance that causes the body to

produce specific antibodies which the antigen can then combine with.

As a rule, antigens are foreign substances, not part of the body's chemistry (most are proteins)

Antibody: a protein produced by B-lymphocytes in response to the presence of an antigen and is capable of combining specifically with the antigen (antibodies have at least 2 antigen-binding sites)

Antibodies react with antigens to form antigen-antibody complexes,which neutralize toxins, inactivate viruses or lyse cells.

ANTIGENS: Immune responses are directed at a series of foreign

substances known as antigens, also referred to as immunosens.

Most antigens are high molecular weight substances, but low molecular weight substances (called hapten) will also act as antigens if they bind to proteins in the body.

The uptake and processing of antigens by macrophages in the tissue is an initial, critical step in most immune responses.

TYPES OF ANTIGENS:Certain types of antigens are distinctive:

a. Autoantisens: are a person's own self antigens.

b. Alloantisens: antigens found in different members of the same species. Ex RBCs antigens A and B

c. Heterophile antisnes: identical antigens found in the cells of different species.

d. Somatic antigens: antigens found on the body cell

e. Capsular antigens: antigens in the bacterial capsule

f. Flagellar antigens: found on an organisms flasella

g. Exotoxins: protein substances that are also antigens.

CLASSES OF ANTIBODIES:Are produced by the plasma cells.=> Five classes:

1. IgM: major component of the primary antibody response in adult humans and is the first antibody to appear in the immune reaction. It cannot diffuse through cell membranes and is found almost exclusively in the blood.

IgG: most common in the bloodstream and is found in many secretions, such as spinal, synovial, lymph fluids, provides natural type of passive immunity.

IgD: extemely small quantities in the serum. Found at the surface of -lymphocytes and believed to be an antigen receptor at this location.

IgE: Occurs in minute concentrations in the serum and is important in hypersensitivity reactions, especially anaphylatic reactions

IgA: found in external secretions such as those at the mucosal surfaces of the respiratory, gastrointestinal, and urogenital tracts. Is present in saliva, bile and urine and is transferred in breast milk.

The reaction of antibodies with antigens helps neutralize the antigen and restrict the spread of infection.

Certain antibodies react with the bacterial surface, while others react with the flagella, pili, or capsules.

These reactions encourage phagocytosis. When antibodies react with a virus, the viruses

cannot attach to the host cells and replicate.

CELLS OF THE IMMUNE SYSTEM: Lymphocytes of the lymphatic system are

derived from stem cells of the bone marrow. These undifferentiated precursors cells

proliferate throughout life and replenish the mature cells of the immune system.

TYPES OF IMMUNITY:

An individual's genetically predetermined resistance to certain diseases is called innate resistance.

Individual resistance is affected by sex, age, nutritional status, and general health.

An individual may develop or acquire immunity after birth.

Immunity is the ability of the body to specifically counteract foreign organisms or substances.

=> TYPES a. Acquired immunity is specific resistance to

infection developed during the life of the individual. Results from the production of antibodies.

b. Naturally Acquired Active Immunity: results from infection and may be long lasting.

c. Naturally Acquired Passive Immunity: antibodies transferred from mother to fetus. Lasts up to a few months

Naturally acquired Active immunity