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INTRODUCTION TO IMMUNOLOGY (CONSEQUENCES OF ANTIGEN-ANTIBODY BINDING…
INTRODUCTION TO IMMUNOLOGY
ANTIBODY
Proteins that recognize and bind to a particular antigen with very high specificity.
Made in response to exposure to the antigen.
Most are bivalent.
Belong to a group of serum proteins called immunoglobulins (Igs).
Ig A
Localized protection of mucosal surfaces. Provides immunity to infant digestive tract.
Ig D
In serum function is unknown. On B cell surface, initiate immune response.
Ig M
First antibodies produced during an infection. Effective against microbes and agglutinating antigens.
Ig E
Allergic reactions. Possibly lysis of worms.
Ig G
Enhances phagocytosis, neutralizes toxins and viruses, protects fetus and newborn.
Immunology
Study of our protection from foreign macromolecules or invading organisms and our responses to them.
IMMUNITY
Adaptive Immunity
Natural
Active
Passive
Artificial
Active
Passive
Innate Immunity
Innate Immunity
react only to microbes,consists of cellular and biochemical defence mechanisms and respond rapidly to infections.
Determinates of Innate Immunity
Species and strains
Age
Hormonal Influences
Nutrition
Cells of Innate Immune system:
Phagocytes
Neutrophils
Eosinophils
Basophils
Mast cells
Responses
Mediated (initiated) by phagocytes, NK cells and soluble proteins
Phagocytes
-Cells specialized in the process of phagocytosis
-Macrophages
-Neutrophils
Phagocytosis
Capture, engulfment and breakdown of bacterial pathogen
Inflammatory response
ADAPTIVE IMMUNITY
immunity develops as a response to infection and is adaptive to the infection
+Specificity for distinct molecules.
+Able to remember and respond more vigorously .
Humoral (antibody mediated) Immunity
Involves production of antibodies against foreign antigens.
Antibodies are produced by B cells.
Antibodies are found in extracellular fluids.
APOPTOSIS
Programmed cell death.
To prevent spread of the infection.
CLONAL SELECTION
B cells (and T cells) that encounter stimulating antigen will proliferate into a large group of cells.
CLONAL DELETION
B and T cells that react against self antigens appear to be destroyed during fetal development.
ANTIGENS
Most are proteins or large polysaccharides from a foreign organism.
Microbes
Capsules, cell walls, toxins, viral capsids, flagella
Nonmicrobes
Pollen, egg white , red blood cell surface molecules, serum proteins,
EPITOPE
Small part of an antigen that interacts with an antibody.Each epitope is recognized by a different antibody.
CONSEQUENCES OF ANTIGEN-ANTIBODY BINDING
Hemagglutination
Agglutination of red blood cells. Used to determine ABO blood types and to detect influenza and measles viruses.
Opsonization
Antigen (microbe) is covered with antibodies that enhances its ingestion and lysis by phagocytic cells.
Agglutination
Antibodies cause antigens (microbes) to clump together.
IgM (decavalent) is more effective that IgG (bivalent).
Antibody-dependent cell-mediated cytotoxicity
Used to destroy large organisms (e.g.: worms). Target organism is coated with antibodies and bombarded with chemicals from nonspecific immune cells.
Neutralization
IgG inactivates viruses by binding to their surface and neutralize toxins by blocking their active sites.
Complement Activation
Both IgG and IgM trigger the complement system which results in cell lysis and inflammation.
Relationship Between Cell-Mediated and Humoral Immunity
Antibody Production
T-Dependent Antigens:
Antibody production requires assistance from T helper cells.
A macrophage cells ingest antigen and presents it to TH cell
T-Independent Antigens:
Antibody production does not require assistance from T cells.
Antigens are mainly polysaccharides or lipopolysaccharides with repeating subunits (bacterial capsules).
Weaker immune response than for T-dependent antigens.
Antibody Dependent Cell Mediated Cytotoxicity
Target cell is covered with antibodies, leaving Fc portion sticking outwards.
Natural killer and other nonspecific cells that have receptors for Fc region are stimulated to kill targeted cells.
Target organism is lysed by substances secreted by attacking cells.
Used to destroy large organisms that cannot be phagocytosed.
CELL MEDIATED IMMUNITY
Involves specialized set of lymphocytes called T cells that recognize foreign antigens on the surface of cells, organisms, or tissues.
Defence against bacteria and viruses that are inside host cells and are inaccessible to antibodies,fungi,cancer cells and transplanted tissue.
T cells
Originate from stem cells in bone marrow followed by migration to thymus gland.
Maturation takes place in thymus gland followed by migration to secondary lymphoid tissue.
Helper T cells
Central role in immune response.
Most are CD4+
Recognize antigen on the surface of antigen presenting cells (e.g.: macrophage).
Activate macrophagesInduce formation of cytotoxic T cells
Stimulate B cells to produce antibodies.
Cytotoxic T cells
Destroy target cells.
Most are CD4 negative (CD4 -).
Recognize antigens on the surface of all cells:
Kill host cells that are infected with viruses or bacteria.
Recognize and kill cancer cells
Recognize and destroy transplanted tissue.
Release protein called perforin which forms a pore in target cell, causing lysis of infected cells.
Undergo apoptosis when stimulating antigen is gone.
