The functions of the immune system in the human body are related to immune response to the entry of foreign components into the body. In protecting the body from disease, the immune system has four main functions: recognition, effect, adjustment, and memory function. Lymphocytes are specific immune systems against pathogen antigens, to ensure that when the next attack of the same pathogen comes, it can be dealt with quickly and vigorously as well as become more immune. These lymphocytes, when formed for the first time, have specific properties, which, in the absence of use, remain in the body as naive. Basically, lymphocytes are divided into two based on their roles, namely, B and T lymphocytes. Activation of T cells will form several types of effector cells, such as cytotoxic, T-helper (Th), and regulator (Treg) cells. Cytotoxics kill pathogens and body cells infected by the virus. Th cells provide additional signals aimed at activating B cells to produce antibodies, also capable of activating other cells such as macrophages to eliminate pathogen in the body. Treg cells function to suppress the activity of the immune system of other lymphocytes so that the immunological reaction does not occur excessively.