Immunity

IMMUNITY

The body’s ability to safeguard itself from pathogens is known as immunity. Our bodies come into contact with many pathogens on a daily basis, yet only a small number of them cause illness. The body can produce antibodies to fight these pathogens and shield the body from illnesses, which is why we refer to this defense mechanism as Immunity.

Immunity is of two types-

Innate Immunity or Natural or Non-specific Immunity

Acquired Immunity or Adaptive Immunity

Innate Immunity

Innate immunity is a type of immunity that is present in an organism from birth and activates promptly when a pathogen attacks. It consists of natural defensive systems such as neutrophils, natural killer cells, salivary enzymes, and undamaged skin. Prior to exposure to pathogens or antigens, this immunity generates a first defense against diseases at birth. The body creates antibodies on its own to provide long-term immunity because it lacks many natural defences against pathogens. Our body has few natural barriers to prevent the entry of pathogens. There are four types of natural barriers which are given below:

Physical barriers: These include skin, body hair, cilia, eyelashes, respiratory tract, and gastrointestinal tract that forms the first line of defense against pathogens. The skin provides fair or dark complexions and acts as a physical barrier, while the mucus coating in the nose and ear traps pathogens before they enter.

Physiological barriers: The stomach uses hydrochloric acid to break down food molecules, killing most germs that enter the body before further processing. Saliva in the mouth and tears in the eyes also have antibiotic properties, preventing pathogen growth even when exposed to them all day.

Cellular barriers: Certain pathogens are able to penetrate our bodies despite the physiological and physical barriers. Leukocytes (WBC), neutrophils, lymphocytes, basophils, eosinophils, and monocytes are the cells that make up this barrier. The blood and tissues contain all of these cells.

Cytokine barriers: Our body’s cells are more intelligent than we realize. When a virus invades a cell in human body, for example, the cell automatically releases

proteins known as interferons, which wrap the infected cell and shield the surrounding cells from infection.

Acquired Immunity

Acquired immunity is pathogen-specific and memory- based, resulting in a low-intensity primary response when the body encounters a pathogen for the first time. This response intensifies with subsequent encounters due to the body’s memory of the first encounter. Primary and secondary immune responses are facilitated by B-lymphocytes and T-lymphocytes, with B-lymphocytes producing antibodies to fight pathogens. T-cells, also known as T-helper cells, assist B cells in producing antibodies,thereby forming the basis of T-helper immunity.

Antibodies, such as IgA, IgM, IgE, and IgG, are produced in the body and are found in the blood. This humoral immune response is one of two types of acquired immune responses:antibody-mediated and cell-mediated immunity (CMI). T-lymphocytes mediate CMI, which helps them kill their own infected cells, preventing the spread of the infection.

How do B cells know which cells are body’s own cells and which are pathogens?

B cells use a receptor to identify foreign-originating proteins attached to cell membranes, determining the cell’s response. These proteins, known as Anti-Body Generating Proteins or Antigens, help B cells decide whether to produce antibodies, as they determine if the cell is foreign-originating and determine the cell’s response.

Active and Passive Immunity

Active immunity is the production of antibodies in the host body when exposed to antigens, such as living or dead microbes or proteins. This type of immunity is slow and takes time to fully respond. Passive immunity involves directly giving ready-made antibodies to protect the body against foreign agents. Mother’s milk, colostrum secreted during lactation, and the placenta during pregnancy are examples of passive immunity. Injecting microbes during immunization or gaining access to the body during natural infection induces active immunity.

Auto Immunity

Auto means ‘self’ and memory-based acquired immunity evolved in higher vertebrates to differentiate foreign organisms from self-cells. Higher vertebrates can distinguish foreign molecules and organisms, which is a focus of

experimental immunology. However, sometimes, due to genetic or unknown reasons, the body attacks self-cells, resulting in damage and an auto-immune disease, such as Rheumatoid arthritis, which affects many people in society.