Immune System – a complex system of cellular and molecular components whose primary function is distinguishing self from nonself and defense against foreign organisms or substances; see also immune response. The primary cellular components are lymphocytes and macrophages, and the primary molecular components are antibodies and lymphokines; granulocytes and the complement system are also involved in immune responses but are not always considered part of the immune system per se.
Source: https://medical-dictionary.thefreedictionary.com/immune+system
