The book How the Immune System Works (How It Works) (2nd Edition) by Lauren M. Sompayrac gives you information how our Immune system works. You may read on this book the functions and structures of the Immune System. Some chapters of this book will state that the immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune

response, the immune system attack organisms and substances that invade our systems and cause disease. The immune system is made up of a network of cells, tissues, and organs that work together to defend the body.

The cells that are part of this defense system are white blood cells, or also known as leukocytes. These leukocytes come in two basic types that seek and destroy the organisms or substances that cause disease. They are also produced or stored in many locations throughout the body that include spleen, thymus, and bone marrow because of this; they are called the lymphoid organs. There are also bundle of lymphoid tissue throughout the body, mostly in the form of lymph nodes that house the leukocytes. These cells circulate through the body between the organs and nodes by means of the lymphatic vessels. They can also circulate through the blood vessels. In this way, the immune system works in a corresponding manner to ensure the body for germs or substances that might cause problems.

The two basic types of leukocytes are:

• Phagocytes, cells that chew up invading organisms.
• Lymphocytes, cells that allow the body to remember and distinguish previous invaders and help the body destroy them.

Few different cells are considered phagocytes. The most common type is the neutrophil, which typically fights bacteria. For an instance, if the doctor worried about a bacterial infection, he might order a blood test to find out if a patient has an increased number of neutrophils triggered by the infection.

Other types of phagocytes have their own functions to ensure that the body response well to a specific type of invader. There are two types of lymphocytes: the B-lymphocytes and the T lymphocytes. These lymphocytes start out in the bone marrow and also stay there and mature into B cells. Moreover, they leave for the thymus gland, where they mature into T cells .B lymphocytes and T lymphocytes have separate jobs to do:

• B-lymphocytes are like the body's military intelligence system, looking for their targets and sending defenses to lock onto them.
• T cells are similar to the soldiers, destroying the invaders that the intelligence system has identified.

In other chapter of this book you will find how these b-lymphocytes and T lymphocytes works. You will discover that the antigens are foreign substances that invade the body. When an antigen is identified, several types of cells work together to recognize and respond to it. These cells trigger the B-lymphocytes to produce antibodies and specialized proteins that lock onto specific antigens. Antibodies and antigens fit together same as a key and a lock. When the B-lymphocytes have produced antibodies, these antibodies keep on existing in a person's body, so that if the same antigen is presented to the immune system again, the antibodies are already there to do their job. That’s why if someone gets sick with a certain disease, like chickenpox, that person normally doesn't get sick from it again. This is also the reason why we use immunizations to prevent getting certain diseases.

The immunization introduces the body to the antigen in such a way that the person doesn’t make sick. However; it does allow the body to produce antibodies that will then keep that person from future attack by the germ or substance that produces that specific disease. Although antibodies can recognize an antigen and lock onto it, they are not capable of destroying it without the help of the T cells.

The T cells are part of the system that eliminates antigens that have been marked by antibodies or cells that have been infected or somehow changed. T cells that are called “killer cells”. They are also involved in helping indicate other cells (like phagocytes) to do their jobs.

Antibodies can also reduce the effect of toxins like poisonous or damaging substances produced by different organisms. Last but not least; antibodies can trigger a group of proteins called complement that are also part of the immune system. This complement assists in killing bacteria, viruses, or infected cells.

All of these specialized cells and parts of the immune system give the body protection against disease. This protection is known as immunity. As you continue to read this book, you will learn how and what immunity is. It will give you comprehensive details about human immune system and its physiological functions.