b and t lymphocytes mediaters of adaptive immune response dr.mohammed sharique ahmed quadri...
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B AND T LYMPHOCYTES MEDIATERS OF ADAPTIVE IMMUNE
RESPONSE
Dr.Mohammed Sharique Ahmed QuadriAssistant professor Physiology
Al Maarefa College
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Objectives
• Describe the different types of lymphocytes
• Discuss the formation and preprocessing of the different types of lymphocytes
• Define clonal selection theory
• Explain the concept of humoral(antibody mediated ) immunity .
• Describe mechanism of action of antibodies
• Emphasis the importance of memory cell ( primary and secondary response)
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Immunity
• Body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells
• Immune system activities– Defends against invading pathogens– Removes “worn-out” cells and tissue damaged by
trauma • Identify and destroy abnormal or mutant cells• Immune surveillance
– Identifies and destroys abnormal or mutant cells that have originated in the body
– Mounts inappropriate immune responses that lead either to allergies or to autoimmune diseases
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Leukocytes • Effectors of the immune system• 5 Types
– Neutrophils• Highly mobile phagocytes that engulf and destroy unwanted materials
– Eosinophils• Secrete chemicals that fight parasites • Involved in allergic reactions
– Basophils• Release histamine and heparin• Involved in allergic reactions
– Monocytes • Transformed into macrophages (tissue-bound phagocytic specialists)
– Lymphocytes • Β lymphocytes (β cells)
– Transformed into plasma cells that secrete antibodies• T lymphocytes (T cells)
– Responsible for cell-mediated immunity
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Lymphocytes
• Mainly produced from lymphoid colonies in lymphoid tissues
• Lymphoid tissues– Tissues that produce, store, or
process lymphocytes– Include
• Bone marrow
• Lymph nodes
• Spleen
• Thymus
• Tonsils
• Adenoids
• Appendix
• Peyer’s patches (GAIT)
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IMMUNITY
• Mechanism by which the body is able to resist or overcome disease causing micro-organisms.
Broadly there are 2 types -
• I. Innate/Non-specific/Natural Immunity
• II. Acquired /Specific/Adaptive Immunity
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I. Innate/Non-specific/Natural Immunity.
Provides first line of defense against infections.
• Intact skin & mucous membranes.• Secretions such as tears, saliva, HCl acid.• Phagocytes & Natural Killer Cells. • Complement system,(a group of 20 proteins
activated by immune complexes)
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Immune Responses
• Innate immune system
– Nonspecific
– Responses work immediately when body is exposed to threatening agent
– Nonselectively defend against foreign invaders
– First line of defense
– Rapid but limited responses
– Neutrophils, macrophages, several plasma proteins are important in innate defense
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Immune Responses
• Adaptive or acquired immune system
– Specifically targets foreign material to which body has already been exposed
– Body has taken time to prepare to attack
– Ultimate weapon against most pathogens
– Responses are mediated by β and T lymphocytes
– Formation of memory cells allows system to react more swiftly against specific invaders in the future
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Adaptive Immunity
• 2 classes of adaptive immunity
– Antibody-mediated or humoral immunity• Involves production of antibodies by B lymphocyte
derivatives known as plasma cells
– Cell-mediated immunity• Involves production of activated T lymphocytes
– Directly attack unwanted cells
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Adaptive ImmunityOrigins of β and T Cells
After early childhood most new lymphocytes are derived from peripheral lymphocyte colonies rather than from bone marrow
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Lymphocytes
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Adaptive Immunity
• Antigen
– Large, foreign, unique molecule
– Induces an immune response against itself
– In general, the more complex a molecule is, the greater its antigenicity
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β Lymphocytes: Antibody-Mediated Immunity
• Each lymphocyte has surface receptors for binding with one particular type of possible antigens- named as BCRs- B-cell receptors
• These are eyes of adaptive immune system
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T-Dependent and T-independent Antigen
• Binding with Antigens stimulate B cells to convert into plasma cells that produce antibodies
• T-independent: after binding with polysaccharide antigen B cells are activated without assistance from T- helper cells
• T-dependent: polypeptide antigen cannot stimulate B cells without the help of T- helper cells
The majority of antigens to which B cell respond are T-dependent
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β Lymphocytes: Antibody-Mediated Immunity
• On binding with processed and presented antigen
– Most B cells differentiate into active plasma cells
– Other B cells become dormant memory cells
• A mature plasma cell then produces antibodies rapidly (2000 antibodies/sec)
• All antibodies eventually enter blood where they are known as gamma globulins or immunoglobulin's
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B -Lymphocytes
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Plasma Cells• Antibody (Immunoglobulin) subclasses
– IgM• Serves as the β cell surface receptor for antigen attachment• Secreted in early stages of plasma cell response
– IgG• Most abundant immunoglobulin in blood• Produced in large amounts when body is exposed to same antigen
– IgE• Helps protect against parasitic worms• Antibody mediator for common allergic responses
– IgA• Found in secretions of digestive, respiratory, and genitourinary
systems; also in milk and tears
– IgD• Present on surface of many β cells• Function is uncertain
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Antibodies• Y-shaped molecules• Composed of 4 interlinked
polypeptide chains– Two long, heavy chains– Two short, light chains
• Properties of tail portion determine functional properties of the antibody( what it will do after binding with antigen)
• Identical antigen-binding fragments (Fab) at tip of each arm (unique for each different antibody)
• Tail (constant region) regions within each subclass are identical
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Mechanism of Action of Antibodies
• Can physically hinder antigens
– By neutralization, they prevent harmful chemicals from interacting with susceptible cells
– Can bind to foreign cells by agglutination
• Enhance activity of other defense systems by
– Activating complement system
– Enhancing phagocytosis
– Stimulating natural killer (K) cells
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Mechanism of Action of Antibodies
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Mechanism of Action of Antibodies
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Immune Complex Disease• Occurs when overzealous antigen-antibody response
causes damage to normal and invading foreign cell
• Antigen-antibody complex normally form in response to foreign invasion and are removed by phagocytic cells
• If large numbers of these complexes are continuously produced, phagocytes can’t clear away all immune complexes formed
– Antigen-antibody complexes not removed continue to activate complement system
– Excessive activated complement damage normal cells
• Can occur in bacterial, viral, or parasitic infections
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Clonal Selection Theory(how matching B cell responds to its antigen)
• During fetal life B cells are genetically preprogrammed to produce antibody against particular antigen , before ever being exposed to it.
• All offspring of particular b lymphocyte form family of identical cells, on exposure to specific antigen . i.e. ( clonal expansion ).
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Clonal Selection Theory(how matching B cell responds to its antigen)
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– Memory cells• Small percentage of β lymphocytes become
memory cells• Remain dormant• Upon re exposure to same antigen, they are
more ready for immediate action than the original lymphocytes of the clone
• Secondary response is quicker, more potent, and longer-lasting
– Can be induced by disease or vaccination
Formation of memory cell can occurs through the person either actually having disease or being vaccinated
Primary and Secondary Response
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Primary and Secondary Immune Responses
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Active and Passive Immunity
• Active immunity
– “self-generated”
– Results from exposure to an antigen
• Passive immunity
– “borrowed immunity”
– Results from transfer of preformed antibodies
– Can provide immediate protection
– Example of passive immunity is transfer of IgG antibodies from mother to fetus
– Tetanus toxins, anti snake venom, rabies virus
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References
• Human physiology by Lauralee Sherwood, seventh edition
• Text book physiology by Guyton &Hall,11th edition• Text book of physiology by Linda .s contanzo,third edition