White blood cells make up our defense against foreign organisms and inner diseases, including autoimmune disease and cancer. They are produced by the bone marrow and have a lifespan of a few weeks. White blood cell count is flexible, and although it has a normal range of 4000-11000 per cubic milliliter, they can change their numbers and increase in response to infections, allergy or cancers. An increased number doesn’t mean that all is well, and a cause has to be sought. The same applies in decreased count, which is called leukopenia.
What can cause leukopenia?
Many causes can lead to a fall in white blood cell count. We will classify them according to the origin of such a low count:
Viral infections have different mechanisms to cause leukopenia. The mechanism depends on the type of virus and the organ it affects. For example, the most common viral infection associated to leukopenia is Epstein-Barr virus, which causes what we call infectious mononucleosis or “kissing fever”. It causes leukopenia through a strong immune response in the T- lymphocytes that are followed by a strong suppression. Epstein-Barr is not the only virus that causes leukopenia through this mechanism, however, and many others have the same mechanism, including herpes, cytomegalovirus, hepatitis C and even HIV.
Other mechanisms by which viruses cause leukopenia may be related to directly shutting down the bone marrow, which is the main manufacturing plant for white blood cells. The most famous is perhaps the Parvovirus B19. Others don’t just affect bone marrow nor on the immune system directly, but have some drug regimens that cause such a condition especially hepatitis C.
Some viruses can also cause cancers that affect white blood cell count negatively, Epstein-Barr virus is linked to many cancers, especially nasopharyngeal cancer, but cancer that causes leukopenia, in this case, is Hodgkin’s lymphoma. The mechanism by which lymphoma can cause leukopenia will be explained later in the article. Hepatitis C virus can also cause leukopenia through inducing acute myeloid leukemia.