Immunization

Immunization is defined as the method of preparing the body to fight against a specific disease. It is a technique used to induce the immune resistance of the body to a specific disease. It is done by subjecting the individual to an antigen in order to produce antibodies against that antigen

PASSIVE IMMUNITY

Passive immunity or immunization is produced without challenging the immune system of the body. This is done bу administration of serum or gamma globulins form a person who is already immunized (affected by the disease) to a non-immune person. Passive immunity can bе acquired either naturally (immunoglobulins G can pass through placenta) or artificially (sera).

ACTIVE IMMUNITY

Active immunity or immunization is acquired by activating immune system of the body. The body develops resis­tance against disease by producing antibodies following the exposure to antigens. Active immunity can be acquired either naturally or artificially.

Active Natural Immunity

Naturally, acquired active immunity involves activation of immune system in the body to produce antibodies. It is achieved in both clinical and subclinical infections.

Clinical infection: During the disease, the plasma cells produce immunoglobulins to destroy the invading anti­gens. Later, due to the activity of memory cells, body retains the ability to produce the antibodies against the specific antigens invaded previously.

Subclinical infection: Some times the disease may not be severe to develop any manifestations. However, it causes the activation of В lymphocytes resulting in produc­tion of antibodies.

Active Artificial Immunity

This type of immunization is achieved by administration of vaccines or toxoids. Vaccines consist of dead pathogens or live but attenuated (artificially weakened) organisms. The toxoids consist of microbial components or toxins secreted by the pathogens.

CYTOKINES

Cytokines are the hormone like small proteins acting as intercellular messengers by binding to specific receptors of target cells. These non-antibody proteins are secreted by white blood cells and some other types of cells. Their major function is the activation and regulation of general immune system of the body.

Depending upon the source of secretion and effects, the cytokines are classified into five types.

1. Interleukins

2. Interferons

3. Colony stimulating factors

4. Tumor necrosis factors and

5. Chemokines

1. Interleukins

The polypeptide cytokines produced mostly by the leukocytes and exerting the effects on other leukocytes are known as interleukins (IL). These cytokines are secreted by helper T cells, other T cells, В cells, monocytes and macrophages. The actions of interleukins are:

• Activation of T cells, macrophages and NK cells

• Promotion of growth of hemopoietic cells and В cells

• Acceleration of inflammatory response by activat­ing eosinophils and

• Chemotaxis of neutrophils, basophils and T cells

So far, about 16 types of interleukins are identified. IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, and IL-8 play important role in the process of immunity. Recently IL-12 (otherwise called natural killer cell stimulatory factor) and IL-II also considered as an important cytokines.