In cell biology, an effector cell is any of various types of cell that actively responds to a stimulus and effects some change (brings it about). Examples of effector cells include: The muscle, gland or organ cell capable of responding to a stimulus at the terminal end of an efferent nerve fiber Plasma cell, an effector B cell in the immune system Effector T cells, T cells that actively respond to a stimulus Cytokine-induced killer cells, strongly productive cytotoxic effector cells that are capable of lysing tumor cells Microglia, a glial effector cell that reconstructs the Central nervous system after a bone marrow transplant Fibroblast, a cell that is most commonly found within connective tissue Mast cell, the primary effector cell involved in the development of asthma Cytokine-induced killer cells as effector cells As an effector cell, cytokine-induced killer cells can recognize infected or malignant cells even when antibodies and major histocompatibility complex (MHC) are not available. This allows a quick immune reaction to take place. Cytokine-Induced killer (CIK) cells are important because harmful cells that do not contain MHC cannot be traced and removed by other immune cells. CIK cells are being studied intensely as a possible therapy treatment for cancer and other types of viral infections. CIK cells respond to lymphokines by lysing tumorous cells that are resistant to NK cells or LAK cell activity. CIK cells show a large amount of cytotoxic potential against various types of tumors. Side effects of CIK cells are also considered very minor. In a few cases, CIK cell treatment lead to the complete disappearance of tumor burdens, extended periods of survival, and improved quality of life, even if the cancerous tumor cells were in advanced stages. At the moment, the exact mechanism of tumor recognition in CIK cells are not completely understood. Fibroblast as effector cells Fibroblast are types of cells that form the extracellular matrix and collagen. Fibroblasts are the most common connective tissues in animals. They have branched cytoplasm surrounding their nucleus, which contain two or more nucleoli. Fibroblasts play a key role when responding to tissue injury. They initiate inflammation in the presence of foreign microorganisms. Receptors found on the surface of fibroblasts regulate hematopoietic cells, start chemokine synthesis, and provide a pathway that allows immune cells to regulate the fibroblast cells. Fibroblasts are also known as tumor mediators. They suppress the tumor as an inflammatory response. Microglia