HUMAN DEFENSE MECHANISM -THE IMMUNE SYSTEM (RESISTANCE TO DISEASE)

           The human beings are surrounded by innumerable harmful agents viz. UV rays in sunlight, chemicals, toxins and various pollutants in our environment, including pathogens. But, despite these deterrants it is a miracle that they still remain healthy. (well, most of the time!). This might be due to the fact that they ate thick skinned (literally) and have a strong defense system.

Resistance

        The human body is armed with a defense system to ward off the damage or disease. This is known as resistance, which is of two general types:

(a) Non-specific (Innate) defenses and (b) Specific resistance.

(a)Non-specific defenses show the following characteristics:

1. It forms the first line of defense.
2. It is present at birth.
3. It shows immediate response.
4. It provides general protection against a wide range of pathogens.
5. The protection is provided by various barriers, such as (i) mechanical (skin,mucocus membrane, hair, tears, saliva, urine, etc.) and (ii) chemical barriers viz. sebum-the acidic film on the skin, lysozyme in tears, saliva, etc., gastric juice (acid) which destroys bacteria and most toxins in the stomach.

(b) Specific resistance or Acquired Immunity or Adaptive Immunity:

This type immunity is characterized by the following features:

•  It develops on contact with a specific invader.
• It shows slow response.
• It involves activation of specific lymphocytes to combat on individual specific pathogen viz. bacteria, virus, toxins, etc.
• It displays two properties: (i) specificity for particular foreign molecules -the antigens, and (ii) memory for most previously encountered antigens.

 Acquired Immunity in turn is of two types:

 (1) In humoral immunity, the body develops circulating  Immunoglobulins orAntibodies which attack and invade the foreign agents. It is directed against extra cellular antigens.

(2) Cell -Mediated Immunity is carried out by specialized cells called 'T' lymphocytes and marcrophages with cyto-toxic properties ("cyto" cell and "toxic" = harmful). It is directed against intra-cellular pathogens viz. viruses, some cancer cells tissue transplants.

The 2011 Nobel Prize for Physiology or Medicine was awarded to Bruce Beulter and jules Hoffmannn jointly for their discoveries concerning the activation of innate immunity & the other hair to Ralph Steinman for the discovery of the dendritic cell and its role in adaptive immunity.