Structure and Function of the Immune System in Dogs

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Below is information about the structure and function of the canine immune system. We will tell you what the immune system is, where it is located, how the immune system works as well as common diseases that affect the immune system in dogs. 

What Is the Immune System in Dogs?

The immune system is a complex network of specialized cells and organs designed to defend a dog’s body against bacteria, viruses, toxins, parasites and any foreign material that invade the dog’s body. Millions of different types of immune cells pass information back and forth, which results in a protective system that is always ready to produce an immune response that is fast and effective. The immune system is also a component of the lymphatic system.

Where Is the Dog’s Immune System Located?

The organs of the immune system are located throughout the dog’s body. They are called lymphoid organs because they are frequently the site of growth, development and deployment of lymphocytes – white blood cells that are key operatives of the immune system.

Important components of the immune system are concentrated in the blood, thymus, lymph nodes, bone marrow, spleen, lungs, liver and intestines. When an infection starts in a location that has only a few components of the immune system, such as the skin, signals are sent throughout the body to call in large numbers of immune cells to the site of the infection.

What Is the General Structure of the Immune System?

The organs of the immune system are connected with one another and with other organs of the body by a network of lymphatic vessels similar to blood vessels. Immune cells, proteins, and sometimes foreign particles are carried through these vessels in lymph, a clear fluid that bathes the body’s tissues. Various components of the immune system are also linked by the circulatory system.

The major components of the immune system include:

  • Lymph nodes. These are small bean-shaped structures lying along the course of lymphatic vessels in particular sites such as the neck, armpit and groin. They filter and trap antigens (the portion of a virus or bacteria that causes an immune response) that arrive at the lymph nodes from the lymphatic vessels and the blood stream.
  • Cells of the lymphocyte portion of the immune system. These cells may be divided into T cells and B cells. T-lymphocytes are initially processed by the thymus gland and are responsible for cellular immunity (the recruitment of other white blood cells to combat infection). B-lymphocytes receive their name from the Bursa of Fabricius, the area in the intestine of birds where these lymphocytes are initially processed. This Bursa does not exist in animals, and most B cells arise in the bone marrow of animals. B-lymphocytes are responsible for making antibodies that are proteins used to fight infections and foreign material. Both of these cells are widely dispersed in the body.
  • The spleen. This organ is located in the upper left quadrant of the abdomen. It filters and traps antigens directly from the blood stream.
  • Bone marrow. Marrow consists of connective tissue, the cells of which form a delicate meshwork within the marrow cavity. The marrow cavity is located in the center of several bones in the body, particularly the long bones. The bone marrow is the site of production of many white blood cells.
  • The thymus. This gland is located in the front part of the chest, just in front of the heart. It is largest in the young animal when the development of the immune system is at its most active, and it shrinks in size as the animal matures.
  • Leukocytes or white blood cells. A variety of white blood cells exist, and each has a special function in the immune system. Some are designed to react primarily to bacteria and inflammation, others react more to parasites and foreign material, and others assist the lymphocytes in producing antibodies.
  • Antibodies. Antibodies are specialized serum proteins produced by B cells in response to antigens. Antibodies are also called immunoglobulins. The body produces several classes or types of immunoglobulins.
  • What Are the Functions of the Canine Immune System?

  • Recognition of foreign substances. Foreign substances that invade the body are called antigens. The immune system has the ability to distinguish between “self” cells (cells of its own body) or “nonself” substances (foreign substances). Every cell in the body carries a molecule that identifies it as “self,” so that the immune system does not attack its own tissues.
  • Protection. Adequate functioning of the immune system provides protection from infectious diseases or other invaders. Antigens may be microorganisms that cause infectious diseases, chemical substances, drugs, certain proteins, transplanted tissues or organs donated from another individual . The immune system may protect the individual from the development of cancer.
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