Microbio: Chs. 15-16 The Human Immune System

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Immunity

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the ability to specifically counteract foreign organisms or substances.

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Antigens

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(Ag) chemical substances that cause the body to produce specific antibodies or sensitized T-cells.

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Antibodies

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(Ab) proteins produced by B-cells in response to the presence of an antigen.
- produced by B cells to recognize, bind with, inactivate, and destroy specific microbes. After their production, these Abs remain in blood plasma, lymph,a nd other body secretions where they protect against the specific pathogens that stimulated their production.

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B-cells and T-cells

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specialized lymphocytes that play a key role in the immune response.

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Acquired Immunity

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Specific resistance to infection developed during the life of an individual.

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Two Basic Types of Acquired Immunity

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-- naturally acquired immunity
-- artificially acquired immunity

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Naturally Acquired Immunity

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- naturally acquired ACTIVE immunity:
- immunity resulting from infection
- may be long lasting

- naturally acquired PASSIVE immunity
- Ab's transferred from mother to developing fetus
- Ab's transferred to a newborn in colostrum
- may last for up to several months.

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Artificially Acquired Immunity

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- artificially acquired ACTIVE immunity
- immunity resulting from vaccination
- may be long lasting
- artificially acquired PASSIVE immunity
- humoral Ab's acquired by injection

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Duality of the Immune System

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1. Humoral Immunity
2. Cell-Mediated Immunity

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Humoral Immunity

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- in HI, a person is immune to a particular pathogen because of the presence of specific protective antibodies that are efective against that pathogen.
- Abs produced by B-cells in response to a specific antigen
- defend against bacteria, viruses and toxins
- HI is found in body fluids (Abs)

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Cell-Mediated Immunity (CMI)

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- due to certain types of lymphocytes.
- depends on T-cells
- does not depend on Ab production
- a response to intracellular bacteria and viruses as well as multicellular parasites, transplanted tissue, and cancer cells.

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Antigen

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- chemical substance that causes the body to produce specific Abs or sensitized T-cells.
- an antibody-generating substance
- most Ags are components of invading microorganisms.

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Chemical Composition of Antigens

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- proteins (most common)
- lipoproteins
- glycoproteins
- nucleoproteins
- large polysaccharides (mw>10,000)

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Antigenic Determinants (Epitopes)

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- specific regions on the surface of an Ag that combines with specific Ab.
- a bacterial cell has many molecules on its surface capable of stimulating the production of Abs; these molecules are called ADs.
- Abs recognize and react with ADs; specific Abs attach to specific ADs

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Hapten

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- small molecular weight substance that cannot cause Ab formation unless combined with a carrier molecule.
- a small molecule may act as an Ag only if it is coupled with a large carrier molecule such as a protein.