Abnormalities in a Cat's Immune System with Cookies Title

Photo Credit: Anssi Koskinen

A cat’s immune system is usually very good at keeping illness at bay. With the huge number of germs that a cat runs into every day, it is amazing that they aren’t sick all of the time. They walk around in the dirtiest areas of our homes and eat creepy crawlers that make it inside! Still, as amazing as a cat’s immune system is, there are times when it falters. Understanding what is going on when that happens could help you to help your cat.

A Quick Review

This is the second in a 3 part series about a cat’s immune system. Please read part 1, A Cat’s Immune System Explained with Cookies, before reading this post. It is quite entertaining and it will make this post make a lot more sense!

A cat’s immune system is supposed to keep that cat’s body free from harmful invaders. Those invaders could be bacteria, fungus, viruses, pollen, or anything foreign from the body. On the inside of the body, the immune system is comprised of a set of specialized white blood cells. Some of these white blood cells are the phagocytes that eat all intruders indiscriminately. Others are lymphocytes like B-cells and T-cells that are “trained” to identify and remember specific invaders and use tactics that are specific to that invader.  The B-cells and T-cells can tell the difference between invaders by the antigens found on the outside of invader. Antigens are small molecular structures on the outside of all cells.

In the examples used in the previous post, all living cells were represented by cookies. The sprinkles, chocolate chips, nuts, frosting, etc were the antigens on the outside of the cookie that helped to identify it. The phagocytes were represented by the Cookie Monster from Sesame Street. Finally, the T-cells and B-cells were represented by Sesame Street’s Martians.

Immune System 2 - Cat's Immune System Cast

You may remember some of these guys from the first post about the cat’s immune system.

A Case of Mistaken Identity

Foreign bodies, like viruses and bacteria, are not the only cells that have antigens. The cell’s of the cat’s own body also have a very specific set of antigens. If a cat’s immune system is functioning properly, then all of the phagocytes and the T-cells and B-cells can recognize the body’s own cells and won’t bother them. However, there are cases in which the T-cells and B-cells get confused and begin identifying the cat’s body’s cells as potentially threatening invaders.

In some cases, medications or diseases, like cancer, are the culprits behind the confusion in the T-cells and B-cells. These can change the shape of the antigens attached the cat’s body’s cells. An example of this is Autoimmune Hemolytic Anemia, in which a change has occurred in the red blood cells. This change causes the red blood cells to be mistaken as invaders by B-cells and T-cells.

Another way that the T-cells and B-cells become confused is when they are improperly “educated” in the lymph nodes. Errors in genetics could be the reason this improper education. The receptor that the T-cell or B-cell uses to identify a specific antigen simply isn’t the correct shape for  that antigen. Instead, the receptor fits on antigens that cover the cells of the cat’s own body.

Other examples of autoimmune disorders in cats include:

Immune System 2 - Autoimmune Reaction comic

Autoimmune reactions look something like this.

Making Mountains Out of Mole Hills

Not all foreign bodies are truly harmful to the body.  Particles of dust or pollen, for example, are not infectious agents looking to take over your cat’s body. However, occasionally the cat’s immune system will overreact to a stimulus, like pollen as if it were a very dangerous strain of bacteria or  virus. When this happens, it is called a hypersensitivity. Allergies are a common form of hypersensitivity.

There are 4 different types of hypersensitivity:

  • Type I (Immediate) – Rapid and severe reactions ( like anaphylaxis) occur when the stimulus is present.
  • Type II (Antibody Mediated) – T-cells and B-cells are creating antibodies against the body’s own cells.
  • Type III (Immune Complex Mediated) – Antibodies created by the T-cells and B-cells bind together with the antigens of the foreign object creating immune complexes. If these immune complexes are not properly  swept away, they can build up in the cat’s organs. Large amounts of these immune complexes lodged in organs can stop the organs from functioning properly.
  • Type IV (Delayed) – A reaction to the stimulus does not occur for more than 24 hours following contact with the stimulus.
Immune System 2 - Hypersensitivity comic

A cartoon example of Hypersensitivity Type I. There is a huge over reaction to some kind of stimulus.

When a cat’s immune system becomes weak.

Keeping a cat healthy is hard work! A cat’s immune system is always fighting microscopic invaders. There are times when the cat’s immune system struggles to keep up. Reasons a cat’s immune system is working at a subpar level can include:

  • Genetic factors that affect the creation or lifespan of immune system cells.
  • Immune suppressing medications.
  • The cat is not receiving enough of certain nutrients in their diet, such as Vitamin A, Vitamin E, Selenium, protein, or calories.
  • The cat has become infected with an illness like FIP, FeLV, or FIV.
Immune System 2 - Immunodeficiency comic

When the cat’s immune system is suppressed, it will have difficulty keeping up with all of the foreign invaders.

Have you ever known a kitty whose immune system had any of these abnormalities?

Sources and Digging Deeper

Hypersensitivity (Acute Allergic) Reactions in Cats: An Abnormal Immune Reaction – Drs. Foster & Smith

Weak Immune System Due to Hereditary Disorder in Cats – Web MD

Immune Deficiency Diseases in Cats  – Merck Manual

Autoimmune Skin Disease in Cats – VCA Animal Hospitals