The key responsibility of white blood cells, also known as leukocytes, is to protect the body from infection. White blood cells formed in the bone marrow take two forms: phagocytes and lymphocytes.
Phagocytes take their name from the Greek word ‘phagein’, which means ‘to devour’. They are cells that exist in the tissues and bloodstream, attacking and consuming alien particles, cellular waste, and bacteria. They serve a critical function in protecting the body against harmful microorganisms, surrounding them and killing them. They come in two forms; granulocytes and monocytes.
Granulocytes defend the body from parasites, fungi and bacteria, with certain granulocytes in charge of handling allergic reactions. Neutrophils form the majority of white blood cells, and are also at the forefront of the defence against bacterial infection. There are also eosinophils and basophils that defend against parasites and respond to allergies.
Monocytes move from the blood to the tissues where they enlarge (become macrophages), consuming alien substances and cell waste.
Just like red blood cells, the manufacture and quantity of phagocytes is strictly controlled by chemicals called interleukins. These chemical messengers trigger the white blood cells to fight infection. While red blood cells stay within the blood system, phagocytes just use the circulatory system as a roadway to access the tissues. The number of phagocytes in the blood is a good indicator of the health status of the body. The neutrophile count goes up when infection is present somewhere in the body. Irregular reactions like a decrease in white blood cells result in poor resistance to bacterial attack. In the end, elements responsible for phagocyte production may turn cancerous, causing myelogenous leukaemia.
These are white blood cells that generate antibodies for attacking harmful organisms, while also removing foreign tissues or cancer cells. The development of lymphocytes in mammals starts in the bone marrow, destined to become either T cells or B cells. The lymphocytes that are meant to defend cells from disease are taken to the thymus, an organ found at the base of the neck, where they are acted upon by hormone to become T cells. These T cells perfrom many functions, particularly fending off viral attacks and cancers. Most T cells stay within the circulatory system, but there are some that stay in the spleen and lymph nodes. B cells perform the function of generating antibodies that mark foreign organisms and substances, making it easy for macrophages to identify and consume them. Low lymphocyte levels make the dog immune-deficient and prone to a host of infections.
Another name given to antibody molecules is immunoglobulin. These are classified according to their respective functions. One category is usually located in the lungs and intestines; another is produced when foreign substances are detected; a third is dominant in the bloodstream; and the final one deals with allergic responses.
Lymphocytes are designed to respond in a particularly way when they detect danger. However, there are times when their response does harm instead of good. One such case is where antibodies are produced to fight the body’s own cells e.g. red blood cells. Another case is inappropriate reaction to allergies. Exposure to allergens might cause the immune system to react in either a mild or life-threatening manner.
In some animals, an elevation in the lymphocyte count could be a response to production of epinephrine, also known as adrenaline. A drop in the number of lymphocytes could be a result of corticosteroid hormones, which are secreted during stressful situations. Vaccinations may also trigger the production of unusual lymphocytes.
Malignant cancerous cells coming from the lymph nodes (lymphoma) or lymphoid leukaemia could also result.