AN INTRODUCTION TO IMMUNITY

 

Everyone in this world has a self-defense system in their body which acts as the immune system and it actually protects our body from different diseases. Immunity can be defined as “the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells”. Some certain cells and organs are responsible for our immunity in the body. Let’s divide the immunity properly.

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Infection occurs when a pathogen invades body cells and starts reproduction. The infection will usually lead to an immune response. If the response is quick and effective, the infection will be eliminated so quickly that the disease will not occur. We can define infection as the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. Sometimes infections lead to disease. The disease can occur when immunity is low or impaired or the virulence of the pathogen is high. Depending upon the infection, the disease symptoms vary greatly. Fever is a common response to infection. Inflammation/swelling is caused by an increase in fluid in the infected area. It is a sign that WBC is on the attack and releasing substances involved in the immune response. Vaccination works to stimulate a specific immune response that will create a specific memory B-cell and T-cell against certain pathogens. These memory cells present in the body can lead to a quick and effective response by which the body can lead to a quick and effective response by which the body can encounter the pathogenic organism.

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Immunity is of 2 types, innate immunity & acquired immunity. Innate immunity is the type of immunity that is inborn immunity or native immunity. Acquired immunity is the type of immunity that is acquired during a lifetime from different incidents.

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body. This immunity is commonly found in invertebrates. It not only activates the complement cascade to identify the microbes, and promotes the clearance of antibody complexes or dead cells but also, activates the adaptive immune system through a process called antigen presentation. The defense mechanisms of innate immunity include sweat, desquamation, flushing, peristalsis, gastric acid, digestive enzyme, thiocyanate, mucus, saliva, lysozyme, tears, etc.

The adaptive immune system also referred to as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminates pathogens by preventing their growth. In contrast to the innate immune system, the acquired immune system is exceptionally explicit to a specific microorganism. The cells that carry out the acquired immune response are white blood cells known as lymphocytes. The acquired immune system is one of the two main immunity strategies that are found in vertebrates. Acquired immunity is further divided into 2 types and they are active immunity, which is generated during interaction with diseases, and passive immunity that develops when an antibody is received from someone.

Both active and passive immunity is divided into Natural and Artificial immunity. Here they are.

1.       Active Natural Immunity: when antibodies are generated after contact with some disease

2.       Active Artificial Immunity: when antibodies are generated after vaccination

3.       Passive Natural Immunity: the immunity received from the mother

4.       Passive Artificial Immunity: the immunity developed by the antibody globule injection

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Some other types of immunity are

·   Humoral immunity: Humoral immunity or humoural immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humor or body fluids.

·   Cell-mediated immunity: Cell-mediated immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

·       Local immunity: The local immunity usually applies at the site of entry of pathogenic microorganisms. In the case of poliomyelitis and influenza, systemic immunizations with killed viruses elicit humoral antibody responses that neutralize the virus as they enter the bloodstream. Natural infection or administration of live oral polio vaccine provides local immunity to gut mucosa and nasal mucosa.

·   Herd immunity: Herd immunity refers to the collective resistance to the disease displayed by the community in its environmental setting. Certain factors like vaccination effects, the carrier plays an important role in herd immunity. When herd immunity is low, there are a large number of susceptible persons in the community and epidemics occur in the introduction to certain pathogens.

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