Immunity

Immunity-

Immunity is defined as the capacity of the body to resist pathogenic agents. It is the ability of body to resist the entry of different types of foreign bodies like bacteria, virus, toxic substances, etc

Immunity is of two types-

  1. Innate immunity. or Native Immunity.
  2. Acquired immunityor Adaptive  Immunity.

1. Innate immunity-

Innate immunity is the inborn capacity of the body to resist pathogens. By chance, if the organisms enter the body, innate immunity eliminates them before the development of any disease. It is otherwise called the Natural or Non-specific immunity.

This type of immunity represents the first line of defence against any type of pathogens. Therefore, it is also called non-specific immunity.

2. Acquired immunity-

Acquired immunity is the resistance developed in the body against any specific foreign body like bacteria, viruses, toxins, vaccines or transplanted tissues. So, this type of immunity is also known as specific immunity.

It is the most powerful immune mechanism that protects the body from the invading organisms or toxic substances. Lymphocytes are responsible for acquired immunity.

Types of Acquired Immunity Two types of acquired immunity develop in the body-

  1. Cellular immunity
  2. Humoral immunity.

Lymphocytes are responsible for the development of these two types of immunity.

The two categories are-

  • T lymphocytes or T cells, which are responsible for the development of cellular immunity
  • B lymphocytes or B cells, which are responsible for humoral immunity.

 Characteristics

  • Antigen specificity- Immune system or antibodies can distinguish among antigens, even between two proteins that differ in only one amino acid.
  • Diversity- Immune system is capable of generating large antibody diversity in its recognition molecules.
  • Immunologic memory- Immune system exhibits memory on second encounter of same antigen by generating a secondary response which is more specific m quick.
  • Self/non-self recognition- Does not react with body’s own molecule but effectively eliminates foreign antigens.

Acquired Immunity Types

1. Acquired Active immunity- 

  • Also known as adaptive immunity.
  • Resistance developed by an individual as a result of an antigenic stimulus.
  • Used for prophylaxis to increase body resistance.

Two types-

A. Natural active immunity-

  •  Results from either a clinical or an inapparent infection by a microbe.
  • Usually long lasting.
  • E.g., person recovering from chicken pox and measles develop natural active immunity.

NOTE- premunition: “special type of immunity seen in syphilis”.

B. Artificial active immunity

  • Resistance induced by vaccination.
  • Vaccines- preparations of live or killed microorganisms and their products (antigens or toxoids)

 Bacterial vaccines-

  • Live or attenuated- BCG for tuberculosis
  • Killed- Cholera vaccine
  • Subunit- Typhoid Vi antigen
  • Bacterial products- Tetanus toxoids

Viral Vaccines-

  • Live or attenuated-oral polio vacine-Sabin
  • Killed-injectable polio vaccine-Salk
  • Subunit-Hepatitis B Vaccine

2. Acquired passive Immunity

  •  Resistance transmitted passively to a receipent in a readymade form.(receipent’s immune system plays no active role)
  •  Used for treatment of acute infection.

2 Types-

A. Natural passive immunity-Resistance passively transferred from mother to foetus or infant, through placenta(transplacentally) and through milk(colostrum).

B. Artificial passive immunity-Resistance passively transferred to a recipient by administration of antibodies.

Agents used-

  • Hyperimmune sera of animal
  • Convalescent sera
  • Pooled human gamma globulin

“These are used for prophylaxis and therapy”.

Active Immunity Passive Immunity
Produced actively by host’s immune system Received passively,no active participation of host’s immune system
Induced by infection or by immunogens Conferred by administration of readymade antibodies
Long-lasting & effective protection Short-term & less effective protection
Immunity effective only after lag period(time required for generation of antibodies.) Immediate immunity
Immunological memory present   No memory
Booster effect on subsequent dose Subsequent dose less effective
Negative phase may occur No negative phase
Not applicable in immunodefficient, Applicable in immunodefficient

 

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