The human body has four main types of lymphocytes: B cells, T cells, natural killer cells, and memory cells.
This article provides an overview of the four main types of lymphocytes found in the human body: B cells, T cells, natural killer cells, and memory cells. It discusses the roles of each type of lymphocyte in the immune system, how they interact with each other, and how they
Natural killer cells, also known as NK cells, are a type of cytotoxic lymphocyte critical to the innate immune system. They are a kind of large granular lymphocyte (LGL), belong to the rapidly expanding family of known innate lymphoid cells (ILC), and represent 5–20% of all circulating lymphocytes in humans. The role of NK cells is analogous to that of cytotoxic T cells in the vertebrate adaptive immune response. NK cells provide rapid responses to virus-infected cells, stressed cells, tumor cells, and other intracellular pathogens based on signals from several activating and inhibitory receptors. While cytotoxic T cells can only activate by detecting the antigen presented on major histocompatibility complex class I molecules on infected cell surfaces, NK cells recognize and kill stressed cells that are lacking the MHC class I molecules. They were named "natural killers" because of the notion that they do not require activation to kill cells that are missing "self" markers of MHC class I. This role is especially important because harmful cells that are missing MHC I markers cannot be detected and destroyed by other immune cells, such as T lymphocyte cells.