IMMUNITY PDF

# IMMUNITY ## Definition It is the capability of our body to fight almost all types of organisms or toxins that tend to damage the tissues and organs. ## Types of Immunity - **Non specific (innate) immunity** - results from general biological processes - Does not depend on Ag invasion - **S...

# IMMUNITY ## Definition It is the capability of our body to fight almost all types of organisms or toxins that tend to damage the tissues and organs. ## Types of Immunity - **Non specific (innate) immunity** - results from general biological processes - Does not depend on Ag invasion - **Specific (acquired) immunity** - Develop specifically against the Ag after it invades the body. ## Basic Classification of Immunity - **Non specific (innate) immunity** - **Specific (acquired) adaptive immunity** - **Humoral immunity** - **Cellular immunity** ## Antibodies - Gamma globulins secreted by plasma cell in lymphoid tissue. Called (Ig) - Each Ab is specific to certain Ag. - Types: 5 types - **Immunoglobulin G (IgG)** - The smallest MW. - Highest concentration 75%. - Cross the placenta, passive immunity. - Rh antibodies are IgG. - **Immunoglobulin M (IgM)** - The largest MW. - Can not pass placenta. ## NON SPECIFIC IMMUNITY - Skin barrier resist invasion. - Acidity of stomach. - Phagocytic cells. - Substances in the blood such as: - Lysozymes. - Basic polypeptides. - Natural killer cells (non T non B lymphocytes). - Complement complex. ## Mechanism of action of Antibodies - **Igs** - **Direct action:** - Directly attack the invader. - Mechanisms: - Agglutination (agglutinins). - Precipitation (precipitins). - Neutralization (antitoxin). - Lysis (lysins). - **Indirect action** - By activation the complement system and then attack the Ag through: - Agglutination. - Opsonization. - Neutralization. - Lysis. - Chemotaxis. - Inflammation. - **Immunoglobulin A (IgA)** - Acts as topical local immune system, called secretary Ig, or cytophilic Ig - **Immunoglobulin D (IgD)** - Acts as Ag receptors on the surface of lymphocytes. - **Immunoglobulin E (IgE)** - Usually attached to the basophil and mast cell surfaces +++their secretions. e.g. histamine. ## Diagram of an Antibody - The diagram shows an antibody with two "arms". - Each arm has a variable region at the top, which binds to a specific antigen. - The rest of the "arm" has a constant region. - The two arms are connected by a hinge region. - The antibody also has two light chains and two heavy chains. ## Diagram of different types of antibodies - The diagram shows the 5 types of antibodies. - **IgG** is the most common type of antibody. - **IgM** is the largest antibody and is the first antibody produced during an infection. - **IgA** is found in saliva, tears, and mucus and helps to protect the body from infection. - **IgE** is involved in allergic reactions. - **IgD** is found on the surface of B cells and helps to activate them. # SPECIFIC (ACQUIRED) ADAPTIVE IMMUNITY - Basic Types Of Acquired Immunity are humoral and cellular immunity. - Both Types are initiated by invasion of Antigens (invasion by a foreign organism or toxin). - The body must have some mechanism for recognizing this invasion. - Because Each toxin or organism always contains one or more specific chemical components (proteins or large polysaccharide) that are different from all other compounds. - Lymphocytes are responsible for acquired immunity. - Lymphocytes that are capable of forming one specific antibody or specific T cell are called a clone of lymphocytes. ## Diagram of B lymphocyte activation - The diagram shows how a B lymphocyte is activated by an antigen. - The antigen binds to the B cell receptor, which activates the B cell. - The activated B cell then proliferates and differentiates into plasma cells and memory B cells. - Plasma cells produce antibodies that target the antigen. - Memory B cells can quickly respond to future infections with the same antigen. ## Diagram of the mechanisms of antibody action - **Precipitation**: Makes soluble antigens insoluble, aiding elimination. - **Agglutination**: Links cell-bound antigens together, causing clumping. - **Neutralisation**: Masks dangerous parts of pathogen (eg. exotoxins, etc.). - **Inflammation**: Triggers histamine release, increasing immune mobility. - **Complement**: Complement protein perforates the cell membrane (cell lysis). ## Composition of antibodies - **IgG, IgA, IgD and IgE are Y shaped.** - Y shaped Igs consist of 4 polypeptide chain 2 light chains, - and 2 heavy chain connected by disulphide bonds. - The Ag binding site lies between heavy and light chains. - **IgM consist of 5 units (pentamer) it has 10 Ag binding sites.** ## Humoral immunity (antibody mediated immunity) - Definition: It is immunity mediated by circulating Abs. - Mechanism of humoral immunity: - Activation of B lymphocytes(specific B lymphocyte clone). - Formation of plasma cell and Abs. - Formation of memory cell enhances AB Response to Subsequent Antigen Exposure. - Inhibition of AB production by suppressor cells. ## Mechanism for activating a clone of lymphocytes - Each B lymphocyte, has on its cell surface membrane about 100,000 antibody molecules that will react highly specifically with only one type of antigen - Each T lymphocyte has on its cell surface membrane proteins (surface receptor proteins or T-cell markers) that are highly specific for one specified antigen. ## The Complement System - A system of about 20 proteins. - They are 11 proteins designated C1 - C9, B, and D. - When activated lead to production of complement products result in many effects. # Specific acquired immunity - Humoral immunity # CELL MEDIATED IMMUNITY - Definition: It is immunity mediated by T lymphocytes - Mechanism of cell mediated immunity: - Activation of T lymphocytes as b lymphocytes - Formation of effector T cells (Activated) - Cytotoxic T. cell - Helper T cell - Suppressor T cell - Formation of memory cells - Suppression of the effector T cells by ## Humoral Immune Response - **Primary response** - Initial encounter with antigen. - B lymphoblasts proliferate to form a clone. - Antigen binding to a receptor on a specific B lymphocyte (B lymphocytes with non-complementary receptors remain inactive). - Plasma cells secrete antibody molecules. - **Secondary response** - Can be years later. - Clone of cells identical to ancestral cells. - Plasma cells secrete antibody molecules. - Memory B cells. - Subsequent challenge by same antigen. ## Diagram of the humoral and cellular response - The diagram shows the humoral and cellular response to a foreign body. - The humoral response involves B cells producing antibodies that target the foreign body. - The cellular response involves T cells directly attacking the foreign body. ## Types of Activated Effectors T cells - **Cytotoxic T cells killer cells** - Directly kill the pathogens, viral infected cell, cancer cells, and transplanted cells through release hole forming protein (perforin) - make holes in their surfaces and allow ISF entering the cell leading to its rupture- - Also release cytotoxic substances into the cells. - **Suppressor T cells inhibit B and other T lymphocytes. So prevent excessive stimulation of immune response.**