Structure and Function of the Immune System in Cats

Structure and Function of the Immune System in Cats

By: Virginia Wells

What Are the Common Diseases of the Immune System?

Disorders of the immune system fall into three major categories: immune deficiencies, immune-mediated diseases, and cancer of the immune system.

  • Immune deficiencies may be inherited and congenital or may be acquired at some time during life. Congenital immune deficiencies usually reflect abnormal function of one or more white blood cells, the inability to produce normal numbers of white blood cells, or an inability to produce antibodies. Congenital under development of the thymus is also possible. Acquired immune deficiencies may develop in association with other systemic diseases, such as sugar diabetes; infection with the feline leukemia virus, feline immunodeficiency virus, or feline infectious peritonitis virus; and cancer.


  • Immune-mediated diseases include any disorder in which the immune reaction mounted by the body is harmful to the body, or when the immune reaction is mistakenly directed against parts of the body's own organs. Examples of immune-mediated diseases include allergic reactions to food, drugs, vaccines, insect bites; anaphylaxis, a life-threatening allergic immune reaction; atopy or allergic skin disease from inhaled allergens; allergic bronchitis (feline asthma); immune-mediated hemolytic anemia where the body attacks its own red blood cells (rare in cats and often associated with certain infections); lymphocytic plasmacytic pododermatitis, an immune disease of the tissues of the foot; pemphigus complex, which is a group of immune-mediated diseases of the skin and mucous membranes characterized by blisters and ulcerations; and immune-mediated polyarthritis, an inflammatory joint disease.

  • Cancer of the immune system usually involves the over production of immune cells, and may result in the over production of immunoglobulins. Cancer of the immune system may arise as a solid tumor or a circulating leukemia of white blood cells, or as a tumor of the thymus, spleen, lymph nodes or bone marrow.

    What Types of Diagnostic Tests Are Used to Evaluate the Immune System?

  • Complete blood count, with differentiation of the types of white blood cells present in the blood.

  • A chemistry profile and a urinalysis

  • Bone marrow aspirate or biopsy and cytology

  • Fine needle aspirate and cytology of any abnormal lymph nodes, spleen or thymus

  • Chest X-rays to evaluate the size of the thymus

  • Abdominal X-rays and ultrasonography to evaluate the spleen and other abdominal organs

  • Specialized immune function tests, such as a Coombs test, measurement and classification of immunoglobulins in the blood, antinuclear antibody (ANA) assay, a lupus cell assay, lymphocyte transformation test, neutrophil function test

  • Removal and biopsy of abnormal immune tissues

  • Serologic tests that detect infectious diseases that can affect the immune system, particularly the feline viral diseases

  • Intradermal and serum allergy testing

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