White blood cells in the human body are designed to defend the organism from external attacks. When leukocytes are low, a patient is susceptible to infection. First you may be wondering, what are lymphocytes exactly? Lymphocytes function are a type of white blood cell that is distinguished from the rest by a lack of granules. Lymphocytes function play a key role in the immune system. This is because lymphocytes are able to respond to unknown agents by producing antibodies made to defend against viruses and tumor cells [1] .