You and your dog have lymphocytes, a type of white blood cell that plays an important role in your immune systems. If your veterinarian tests your pup's blood and finds an abnormal level of lymphocytes, an active infection or some other type of health issue may be at hand.
White Blood Cells
Fido's blood contains both red blood cells and white blood cells, which perform important functions in his body. The white blood cells, also referred to as leukocytes, are a vital part of his immune system, constantly monitoring his body for signs of bacteria, viruses, fungi and parasites. All of Fido's white blood cells are either granulocytes or agranulocytes, according to PetEducation.com. Lymphocytes and monocytes are agranulocytes, while neutrophils, basophils and eosinophils are granulocytes. Your pup's body produces lymphocytes in what is called his lymphoid tissue, which includes his lymph nodes and spleen. Overall, canines have fewer lymphocytes in circulation than neutrophils, according to author and veterinarian Susan M. Cotter in "Hematology."
Lymphocytes Fighting Invaders
While some leukocytes get rid of invading organisms in your pup's body by digesting them, others, including lymphocytes, help the body fight off these invaders in other ways. Your pup has two types of lymphocytes, namely T cells and B cells, according to the petMD website. Both B and T cells work together, sharing the information they discover about infectious microorganisms to coordinate attacks on them. B cells gather information about potential threats to the body and use them to produce protein molecules called antibodies. These antibodies attach onto any invading microorganisms and mark them as dangerous. T cells then use this information to activate other types of cells, like neutrophils, to physically attack and destroy the marked invading organisms.
The Body's Memory System
Once your pup's lymphocytes produce antibodies against a particular disease-causing agent, called an antigen, those antibodies stay in his body. If the antigen appears again, Fido can fight it off immediately, thus giving him immunity against it. This is why immunizations are important for protecting your dog against potentially deadly and contagious diseases like rabies, distemper, parvovirus and canine hepatitis. When your pup is immunized against disease by your vet, the vaccinations won't actually make Fido sick but will trigger his lymphocytes to produce antibodies against the weakened or dead antigens contained in the vaccine. This provides him with immunity against the diseases they cause.
Unusual Lymphocyte Levels
One of the main ways your vet will check for any diseases in Fido is by performing a routine complete blood count. She'll take your pup's blood and check the level of white blood cells in it. While the test will not specifically test for lymphocyte levels, the total number of white blood cells can give her an idea of whether an infection is present in his body. If Fido's white blood cell count is unusual, your vet may order more detailed blood tests, such as a CBC with differential test, to check for the specific levels of lymphocytes in his blood. A decreased level of the cells can indicate an active infection, while an elevated level could indicate a chronic infection, autoimmune disease or leukemia.