Specific Defense Mechanisms – The Immune System
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Transcript of Specific Defense Mechanisms – The Immune System
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Specific Defense Mechanisms Specific Defense Mechanisms – The Immune System– The Immune System
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The Immune System The Immune System – 3– 3rdrd Line of Defense Line of Defense
Antigen specific – recognizes and acts against particular foreign substances
Systemic – not restricted to the initial infection site
Has memory – recognizes and mounts a stronger attack on previously encountered pathogens
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Types of ImmunityTypes of Immunity1. Humoral immunity
Antibody-mediated immunity
Cells produce chemicals for defense
2. Cellular immunity Cell-mediated
immunity Cells target virus
infected cells
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Antigens (Nonself)Antigens (Nonself) Any substance capable of exciting the
immune system and provoking an immune response
Examples of common antigens- Foreign proteins- Nucleic acids- Large carbohydrates- Some lipids- Pollen grains- Microorganisms
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Self-AntigensSelf-Antigens
Human cells have many surface proteins
Our immune cells do not attack our own proteins
Our cells in another person’s body can trigger an immune response because they are foreign
- Restricts donors for transplants
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AllergiesAllergies
Many small molecules (called haptens or incomplete antigens) are not antigenic, but link up with our own proteins
The immune system may recognize and respond to a protein-hapten combination
The immune response is harmful rather than protective because it attacks our own cells
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Cells of the Immune SystemCells of the Immune SystemLymphocytes
Originate from hemocytoblasts in the red bone marrow
B lymphocytes become immunocompetent in the bone marrow
T lymphocytes become immunocompetent in the thymus
Macrophages Arise from monocytes Become widely distributed in lymphoid organs
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Activation of LymphocytesActivation of Lymphocytes
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Humoral Humoral (Antibody-Mediated)(Antibody-Mediated) Immune ResponseImmune Response B cells w/ specific receptors bind to specific antigen Binding activates the B-cell to undergo clonal selection Many clones are produced (1° humoral response)
Most B cells become plasma cells
- Produce antibodies to destroy antigens
- Activity lasts for four or five days Some B cells become memory cells (2° humoral response)
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Humoral Immune ResponseHumoral Immune Response
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Secondary ResponseSecondary Response
Memory cells are long-lived
A second exposure causes a rapid response
The secondary response is stronger, faster & longer lasting
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Active ImmunityActive Immunity
Your B cells encounter antigens and produce antibodies
Active immunity can be naturally or artificially acquired
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Passive ImmunityPassive Immunity
Antibodies are obtained from someone else- mother to fetus
(placenta or milk)- Injection of immune
serum or gamma globulin
Immunological memory does not occur
Protection provided by “borrowed antibodies”
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Monoclonal AntibodiesMonoclonal Antibodies Antibodies prepared for clinical testing
or diagnostic services Produced from descendents of a single
cell line Examples of uses for monoclonal
antibodies- Diagnosis of pregnancy- Treatment after exposure to hepatitis and
rabies
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Antibodies (Immunoglobulins) (Igs)Antibodies (Immunoglobulins) (Igs) Soluble proteins secreted by B cells
(plasma cells) Carried in blood plasma Capable of binding specifically to an
antigen
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Antibody StructureAntibody Structure Four amino acid
chains linked by disulfide bonds
Two identical amino acid chains are linked to form a heavy chain
The other two identical chains are light chains
Specific antigen-binding sites are present
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Antibody ClassesAntibody Classes
Antibodies of each class have slightly different roles
Five major immunoglobulin classes IgM – can fix complement IgA – found mainly in mucus IgD – important in activation of B cell IgG – can cross the placental barrier IgE – involved in allergies
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Antibody FunctionAntibody Function
Antibodies inactivate antigens in a number of ways Complement fixation Neutralization Agglutination Precipitation
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Antibody FunctionAntibody Function
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Cellular Cellular (Cell-Mediated)(Cell-Mediated) Immune Response Immune Response
Antigens must be presented by macrophages to an immunocompetent T cell (antigen presentation)
T cells must recognize nonself and self (double recognition)
After antigen binding, clones form as with B cells, but different classes of cells are produced
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Cellular Cellular (Cell-Mediated)(Cell-Mediated) Immune Response Immune Response
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T Cell ClonesT Cell ClonesCytotoxic (Killer) T cells
Specialize in killing infected cells Insert a toxic chemical (perforin)
Helper T cells Recruit other cells to fight the invaders Interact directly with B cells
Suppressor T cells Release chemicals to stop T and B cells Stop the immune response to prevent
uncontrolled activity
A few members of each clone are memory cells