Cancer and the Immune System: The Human Immune Defense System

Cancer and the Immune System: The Human Immune Defense System

 

THE HUMAN IMMUNE DEFENSE SYSTEM

The environment in which we live contains a wide range of organisms called pathogens that view the human body as a rather juicy target to invade and live off till death do us apart. The job of the mammalian immune system is to defend the body against these pathogens, which include bacteria, viruses, fungi and parasitic worms. This task is so complex that mammals have evolved a very sophisticated network of defense units that recognize and attack such a diverse array of potential enemies. The immune system is characterized by three universal features, which are namely specificity, diversity, and memory. We say the immune system is specific because it only reacts against certain specific molecular targets called antigens. It is very important that the immune system is able to select what it reacts to because this prevents it from attacking components of our own body: a phenomenon called autoimmunity. The immune system is described as diverse because it has the remarkable ability to react specifically to any molecule in the universe. At the end of a successful immune reaction, the immune system assigns a unique group of immune cells, called memory cells, the task of remembering the particular enemy encountered (virus, bacterium, tumor cell, etc). In this way, there will be immune combat units ready to attack and kill off the fresh invaders very swiftly if they are encountered in the future. The defense system of the human body consists of surface barriers such as skin, internal barriers such as mucus, and special groups of cells, chemicals, and hormones that act in concert to keep the body free of pathogenic invaders. In broad terms, the immune system is divided into two branches called the innate and adaptive defense systems. In evolutionary terms, the innate branch predates the adaptive branch by about 500 million years. In the next three sections, the reader will be introduced to both the innate and adaptive immune systems. These sections will also examine how the two systems communicate effectively to bring about a coordinated defense of their host organisms.

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