What is Immunity and Types of Immunity?
Immunity is the ability to resist a particular infection or toxin by the action (releasing) specific antibodies or sensitized white blood cells. Immunity is defensive mechanism. It is divided into two types.
- Non specific defence mechanism: It is most effective on invaders. Example for this mechanism is skin. The protection provided by the skin from various microbes and dust particles. Another examples is Mucus secreted by mucus membrane traps microbes and other foreign materials.
- Specific defence mechanism: In this mechanism body identifies the substance and generates a specific response to particular substance. These substances are called as Antigens ( bacteria, cancer cell etc….).
Types of Immunity
Majorly two types of Immunity one is the Inborn, and the other is Non-specific or later Acquired in life and specific Immunity.
- Innate Immunity – The Immunity attained by birth through their Maternal and Paternal genetic nature is known as Innate Immunity. This is Non-specific. Human body contains different physical and chemical barriers to protect against infectious agents. Skin contains sweat and sebaceous glands and their secretions will protect us by killing harmful agents. Mucous, lachrymal secretions, complement system, Cytokines etc., protects us from infectious foreign cells. Inflammation is best kind of Innate Immunity.
- Acquired / Adaptive Immunity – The Immunity attained by the body after birth, in response to fight against infections or disease causing pathogens is called Acquired Immunity. This in-turn is classified into two types. A) Natural Immunity with Active and Passive Immunity and B) Artificial Immunity with Active and Passive Immunity.
- Natural Active Immunity – It is attained naturally against the antigens either by producing antibodies from B-lymphocytes or direct killing by T-lymphocytes.
- Natural Passive Immunity – It is attained, when the Antibodies passes from Mother to fetus via placenta or to infants through milk.
- Artificial Active Immunity – It is attained, by introducing vaccines, the biological inactivated toxins or toxoids.
- Artificial Passive Immunity – It is attained, by injecting preformed antibodies artificially into the serum.
Types of Immune responses
Based on the type of cells involved, the Immune responses are of two types.
- Cell mediated Immune response – The Immune response mediated by the T-Cytotoxic cells with the help of T-Helper cells is known as Cell mediated Immune response. It does not involve the antibody production, but involves the activation of phagocytes and release of cytokines.
- Humoral mediated Immune response – The immune response mediated by the the cells of humors or body fluids. These are macro-molecules found in extracellular fluids. Exactly to say, it is mediated by Antibodies produced by plasma cells of B-lymphocytes and act against antigens producing Antigen-Antibody reactions.
Structure of Antigen
The substance that induces specific Immune response and interacts with the products formed is known as an Immunogen. It is protein in nature and its Epitopes(binding site of Ab) are the antigenic determinants. Haptens becomes immunogenic or antigenic, only when attached to a large protein carrier.
Structure of Antibody
- The Globular plama protein components released by the plama cells of B-lymphocytes to produce an Immune response are known as Immunoglobulins or Antibodies.
- They contain four polypeptides, two Heavy chains and two Light chains joined together forming a Y-shaped structure.
- Two fragments Fab and Fc are present in which the fragment antigen-binding (Fab) specifically helpful in recognizing and attachment of antigen to the antibody.
- The crystallisable fragment (Fc) region interacts with other elements of immune system.
- It also contains one constant and one variable domain from each heavy and light chain of antibody.
- The region of antibody which binds to the epitope of antigen is called Paratope and it will be present at the variable region of antigen binding site.
Types of Antigen-Antibody Reactions
The Antigens ad Antibodies specifically interact with each other and produces Humoral or Antibody mediated Immune response. These reactions used to detect the infectious disease causing agents. Antigen binds covalently to the antibody specific site. Different types of Ag-Ab reactions are,
- Antibody-mediated cytotoxicity
- The Complement activation membrane Attack complex.