There are many cell types with their own specific roles involved in immunity. In the innate immune response, these include macrophages, neutrophils, eosinophils, basophils, mast cells and dendritic cells that are derived from myeloid progenitors. Natural killer cells also form part of the innate immune system but, unlike the other cells of the innate immune system, are derived from lymphoid stem cells. Cells involved in the adaptive immune response include B cells (or B lymphocytes) that differentiate into memory cells and plasma cells and a variety of T cells (or T lymphocytes), including T helper cells and cytotoxic T cells (also called cytotoxic T lymphocytes, CTLs and CD8+ T cells), that are derived from lymphoid stem cells. Natural killer T cells and gamma-delta T cells are part of both the innate and adaptive immune response.