• Immunity is the process of recognization, elimination, neutralization or destruction of foreign substance from the body which may be beneficial or harmful for the host.
  • The term immunity refers to all the mechanisms used by the body to resist against environment agent that are foreign to it.
  • Immunity is defined as all those physiologic mechanisms that endow the animal with the capacity to recognize materials as foreign to itself and then to neutralize, eliminate or metabolize them. Although the usual outcome of immune response is beneficial, it may cause harmful or detrimental effects such as autoimmunity and hypersensitivity.

Beneficial effect of immunity:

  1. Clinical & subclinical infection produces specific immunity. When an individual suffers from measles, small pox, chicken pox, he or she develops lifelong immunity against these viruses.
  2. Vaccination produces specific immunity artificially e.g. DPT vaccination prevents Diphtheria, pertussis & Tetanus.

Harmful effect of immunity

  1. Hypersensitivity stares like asthma, rheumatic fever, glomerulonephritis, etc.
  2. Autoimmune diseases like rheumatoid arthritis, SLE, Autoimmune hemolytic anemia, etc.

Classification of immunity:

  1. Innate immunity:

Innate immunity (also called natural or native immunity) refers to defense mechanisms that are present even before exposure to the antigen. It is non-specific.

  1. Acquired immunity:

Acquired immunity (also called adaptive or specific immunity) refers to the defense mechanisms that develop after exposure to an antigen, improves upon repeated exposure, and is specific.

  1. Active immunity: it is that type of acquired immunity which immunocompetent cells of the body participate actively. It is of two types-
  2. Natural immunity: active immunity which develops after clinical& subclinical infection is called natural active immunity.
  3. Artificial immunity: Active immunity which develops after vaccination is celled active immunity e.g. DPT vaccine produces immunity against diphtheria, pertussis & tetanus.

2. passive immunity: it is that type of acquired immunity where performed antibody is introduced into a host to produce a specific immunity. It is of two types-

a. Nature immunity: the immunity caused by passing lgG antibody from mother to fetus during pregnancy through a placental route & lgA antibody from mother to newborn during breast milk is celled nature passive immunity: these antibodies offer immunity for 6 months birth.

b. Artificial immunity: Administration of antibodies performed in another host produces artificial passive immunity e .g. ATS (anti-tetanus serum), ADS (anti- diphtheria serum) TIG (tetanus immunoglobulin) produce artificial passive immunity.

According to type of cell involved: Active immunity is divided into 2 types-

  1. Cell mediated immunity (CMI): T cell participates in CMI
  2. Humoral immunity (HI): B-cell participates in HI and produces antibody.

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