Complement System

Living organisms are surrounded by numerous types of bacteria, fungi, and viruses etc. which can intrude into the body and cause damage. These invaders are called antigens (or pathogens-disease causing antigens). A living body has its own defense mechanism to prevent the invasion of these pathogens. This defense mechanism comprises of various cells, tissues and chemical substances and is termed as Immune system. The study of immune system is called Immunology. Immune system is mainly of two types: Innate (non-specific) Immunity and Acquired (Specific) Immunity.

Innate Immunity

All those defense mechanisms with which n individual is born, constitute the innate immunity. These mechanisms are:

• Anatomical barrier.
  It blocks the entry of foreign bodies with mucous membrane, skin etc.
• Physiological barrier
  Itstops the growth of pathogen with body temperature, secretions etc.
• Phagocytic barrier
  Phagocytes are blood cells which engulf and destroy the foreign body.
• Inflammatory barrier
  It prevents the infection at the site of infection locally.

Acquired Immunity

Immunity acquired after birth. It can recognize and eliminate specific infection.

Complement System

In vertebrates, another effective defense mechanism exists, which is called complement system. It is a part of both innate and acquired immune systems. It consists of a group of proteins that circulate freely in blood plasma. In time of infection by a pathogen, these proteins aggregate and form a membrane attack complex. It enters into the pathogenic cell and makes it swell and burst. Thus the pathogen is destroyed. Some complement proteins coat the pathogen, which then is attacked by phagocytes and get destroyed. The complement systems carry on mainly the defense following functions.

• trigger inflammation
• attract phagocytes to the infection site
• promote the attachment of antigens to phagocytes
• cause bursting out (lysis) of pathogen
• remove harmful immune complexes from the body