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What is the difference between innate and acquired immunity?

Class 12 BiologyNCERT chapter: Human Health and Diseaseइसे हिंदी में पढ़ें

Exam-ready answer

Innate immunity is non-specific defence present at birth; it acts through physical, physiological, cellular and cytokine barriers against any foreign agent. Acquired immunity is pathogen-specific, develops after meeting a pathogen and is characterised by memory: the first encounter gives a low-intensity primary response, and a later encounter gives a highly intensified secondary response.

Explanation

Innate immunity is inborn and does not depend on which microbe attacks. It has four kinds of barriers. Physical barriers are the skin and the mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts, which traps microbes. Physiological barriers are acid in the stomach, saliva in the mouth and tears from the eyes, which all prevent microbial growth.

Cellular barriers are leukocytes such as polymorpho-nuclear leukocytes (neutrophils), monocytes and natural killer lymphocytes in the blood, and macrophages in tissues; they phagocytose and destroy microbes. Cytokine barriers are proteins called interferons, secreted by virus-infected cells, which protect non-infected cells from further viral infection. These defences act in the same way every time; they do not become stronger on a second exposure.

Acquired immunity is carried out by two types of lymphocytes. B-lymphocytes produce antibodies into the blood, giving the humoral immune response. T-lymphocytes help B-cells and mediate cell-mediated immunity, which is responsible for graft rejection. Memory cells formed during the first exposure give a faster and stronger secondary, or anamnestic, response. Acquired immunity can be active, after infection or vaccination, or passive, when ready-made antibodies are given.

Points to remember

  1. Innate immunity: non-specific type of defence present at the time of birth.
  2. Four barriers of innate immunity: physical, physiological, cellular and cytokine barriers.
  3. Acquired immunity: pathogen-specific and characterised by memory.
  4. Primary response on first encounter is of low intensity; secondary (anamnestic) response is highly intensified.
  5. B-lymphocytes produce antibodies (humoral immunity); T-lymphocytes mediate cell-mediated immunity (CMI).

Exam tip

Answer in a two-column table with at least four points: specific or non-specific, present at birth or developed later, presence of memory, and the barriers or cells involved.

Questions students also ask

What is the structure of an antibody?
Each antibody molecule has four peptide chains, two small light chains and two longer heavy chains, so it is represented as H2L2. Different types of antibodies include IgA, IgM, IgE and IgG. They are produced by B-lymphocytes in response to pathogens.
What is the difference between active and passive immunity?
In active immunity the body makes its own antibodies after meeting an antigen, through infection or vaccination; it is slow but long-lasting. In passive immunity ready-made antibodies are given, such as IgA in colostrum fed to a newborn; it acts quickly but does not last long.
Why does a second infection by the same pathogen often cause milder illness?
During the first infection, memory B- and T-cells are formed. On a second exposure to the same pathogen, these cells produce a quick and highly intensified secondary response, so the pathogen is often destroyed before it can cause much illness.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.