Immune system of jawed vertebrates.

A lymphocyte is a type of white blood cell in the immune system of jawed vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adaptive immunity), and B cells (for humeral, antibody-driven adaptive immunity). They are the main type of cell found in lymph, which prompted the name "lymphocyte". [ABSTRACT FROM AUTHOR]