Veterinary IMMUNE SYSTEM (Animals)

   IMMUNE SYSTEM                        

    (Animals)

Definition

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 attacks organisms & substances that invade body systems and cause disease.

The immune system is made up of s network of cells, tissues, and organs that work together to protect the body. The cells involved are white blood cells, or leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substences.

Leukocytes are produced or stored in many locations in body, including the thymus, spleen, and bone marrow. For this reason, they are called the lymphoid organs. There are also clumps of lymphoid tissue throughout the body, primarily  as lymph nodes, that house the leukocytes.

The leukocytes circulate through the body between the organs and nodes via lymphatic vessels and blood vessels. In this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might cause problems.

Types

Two basic types of leukocytes

ð       Phagocytes, cells that chew up invading organisms

ð       Lymphocytes, cells that allow the body to remember and recognize previous invaders and help the body destroy them.

A number of different cells are considered phagocytes. The most common type is the neutrophil, which primarily fights bacteria, If doctors are worried about a bacterial infection, they might order a blood test to see if a patient has an increased number of neutrophils triggered by the infection. Other types of phagocytes have their own jobs to make sure that the body responds appropriately to a specific type of invaders.

Two types of lymphocytes

1.    B  lymphocytes

2.    T  lymphocytes

Lymphocytes start out in the bone marrow and either stay there and mature in to B cells, or they leave for the thymus gland, where they mature in to T cells. B lymphocytes and T lymphocytes have separate functions.

                               B lymphocytes are like the body`s military intelligence system, seeking out their targets and sending defenses to lock on to them.

                              T cells are like the soldiers,  destroying the invaders that the intelligence system has identified.

Functions

When antigens are detected, several types of cells work together to recognize them and respond. these cells trigger the B lymphocytes to produce antibodies, specialized proteins that lock on to specific antigens.

Once produced, these antibodies continue to exist in a persons`s body, so that if the same antigen is presented to the immune system again, the antibodies are already to do their job. So if someone gets sick with a certain disease, like chickenpox, that persons typically doesn`t get sick from it again. This is also how immunizations prevent certain diseases. An immunization introduces the body to an antigen in a way that doesn`t make someone sick, but does allow the body to produce antibodies that will then protect the persons from future attack by the germ or substance that produces antibodies that will then protect the person from future attack by the germ or substances that produces that particular disease. Although antibodies can recognize an antigen and lock on to it, they are not capable of destroying it without help. That`s the job of the T cells, which are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed. T cells also are involved in helping signal other cells to do their jobs.

Antibodies also can neutralize toxin produced by different organisms. Lastly, antibodies can activated a group of proteins called complement, that are also part of the immune system. Compliment assists in killing bacteria, viruses, or infected cells. All of these specialized cells and parts of the immune system offer the body protection against disease. This protection is called immunity.