Question

Describe the different types of immunity.

Answer 1

There are two types of immunity i.e. Innate or Inborn (inherited) immunity and Acquired or Adaptive immunity.

i. Innate immunity or Inborn Immunity:

Innate immunity is the resistance to infections that an individual possesses genetically.

It is the natural (inborn) defense system of the body.
It is not affected by prior contact with microorganisms or immunization.
It is non-specific when it indicates a degree of resistance to infection in general.
Innate immunity comprises the various types of barriers that prevent the entry of foreign agents into the body.

a. Epithelial surface: The intact skin and mucous membranes (secrete mucously) covering the body, protects against invasion by a microorganism(s).
Healthy skin possesses bactericidal activity due to the presence of high concentrations of salt in drying sweat. Sebaceous secretions and a long chain of fatty acids have bactericidal and fungicidal properties.
The mucosa of the respiratory tract has several innate mechanisms of defense.

The nose prevents the entry of microorganisms to a large extent, the inhaled particles being arrested through the hair at or near the nasal orifices.
Those foreign particles that pass the nasal orifices are held by the mucus lining the epithelium and are swept back to the pharynx where they tend to swallow or coughed out.
The cough reflex is an important defense mechanism of the respiratory tract. The mouth is constantly bathed in saliva which has an inhibitory effect on microorganisms. The acidity of gastric secretions in the stomach destroys micro-organisms.
The flushing action of urine eliminates bacteria from the urethra.
Spermine and zinc present in semen are antibacterial.

b. Antimicrobial substances in blood and tissues:

The complement system contains more than 30 serum proteins, circulating in the blood in an inactive state. The presence of microbial pathogens activates the ‘Complement cascade’ to eliminate pathogens. The interferons are a class of cytokines (soluble proteins) released by viral cells infected with viruses and certain white blood cells to stimulate other cells to protect themselves from viral infection.

c. Cellular factors in innate immunity:

Natural defense against the invasion of blood and tissues by microorganisms and other foreign particles is mediated to a large extent by phagocytic cells which ingest and destroy them. Phagocytic cells are grouped as macrophages and macrophages. These cells remove foreign particles that enter the body. A class of lymphocytes called Natural killer (NK) cells is important in non-specific defense against viral infections and tumors.

d. Fever:

An increase in body temperature following the infection is a natural defense mechanism. It helps to accelerate the physiological processes to destroy the invading pathogens. Fever stimulates the production of interferons and helps in recovery from viral infections.

e. Acute-phase proteins (APPs):

Infection on injury leads to a sudden increase in the concentration of certain plasma proteins, collectively called acute-phase proteins. These include C Reactive Protein (CRP), Mannose-binding protein, Alpha-1-acid glycoprotein, Serum Amyloid P, etc. APPs are believed to enhance host resistance, prevent tissue injury, and promote the repair of inflammatory lesions.

ii. Acquired immunity:

The resistance that an individual acquires during life is known as Acquired immunity or Adaptive or Specific immunity. It involves the formation of antibodies in the body, which neutralize the antigens.

Acquired immunity is of two types Active and Passive.

a. Active immunity:

It is the resistance developed by individuals as a result of an antigenic stimulus (exposure to antigen).

It also is known as “Adaptive immunity”. Active immunity may be natural or artificial.

1. Natural Acquired Active immunity: Immunity acquired due to infection is called natural active immunity. It is developed after the entry of pathogens into the body. It is long-lasting immunity. e.g. Person who has recovered from an attack of measles develops naturally acquired active immunity to measles, for a lifetime.
2. Artificial Acquired Active immunity: It is the resistance induced by vaccines. The vaccine is introduced into the body to stimulate the formation of antibodies by the immune system. e.g. Polio vaccine, BCG vaccine, etc. such immunity may be temporary or permanent.

b. Passive immunity: Passive immunity is acquired when ready-made antibodies are received by the body cells. i.e. Body cells do not take any active part in the production of immunity. Passive immunity can be acquired either naturally or artificially.

1. Natural Acquired Passive immunity: Before birth maternal antibodies are transferred from mother to fetus through the placenta. After birth, antibodies are transferred from mother to infant through colostrum (first milk of mother) and continue throughout the period of breastfeeding. The antibodies received by the baby from the mother remain in the body for a short time. Therefore, naturally acquired passive immunity is short-lived.
2. Artificially Acquired Passive immunity: This immunity is developed by injecting previously prepared antibodies using serum from humans or animals. e.g. Antibodies obtained from hyperimmunized horses are injected into humans against rabies pathogens. It is short-lived.