Immunity And Human Immune System- Class 12 Biology

The science dealing with the various phenomena of immunity, induced sensitivity and allergy is called immunology.

Types of Immunity:

There is two major types of immunity: innate and acquired immunity.

(A) Innate or Natural or Nonspecific Immunity (L. innatus = inborn)

Innate immunity is inherited by an organism from the parents and protects it from birth throughout life. Innate or nonspecific immunity lacks specific responses to specific invaders. This type of immunity is provided by various barriers present in our body. Innate immunity consists of four types of barriers— physical, physiological, cellular and cytokine barriers.

(B) Acquired Immunity (= Adaptive or Specific Immunity)

The immunity that an individual acquires after the birth is called acquired or adaptive or specific immunity. It is specific and mediated by antibodies or lymphocytes or both which make the antigen harmless.

It not only relieves the victim of the infectious disease but also prevents its further attack in future. The memory cells formed by В cells and T cells are the basis of acquired immunity. Thus acquired immunity consists of specialized В and T lymphocytes and Antibodies.

Characteristics of Acquired Immunity:

(i) Specificity:

It is the ability to differentiate between various foreign molecules (foreign antigens).

(ii) Diversity:

It can recognize a vast variety of foreign molecules (foreign antigens).

(iii) Discrimination between Self and Non-self:

It can recognize and respond to foreign molecules (non-self) and can avoid responding to those molecules that are present in the body (self) of the animal.

(iv) Memory:

When the immune system encounters a specific foreign agent, (e.g., a microbe) for the first time, it generates an immune response and eliminates the invader. This is called the first encounter. The immune system retains the memory of the first encounter. As a result, a second encounter occurs more quickly and stronger than the first encounter.

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