Effector

Effector is a term used in several disciplines to denote an element that produces a response or action in a system upon receiving a stimulus. The precise meaning depends on the field, but the core idea is a component that directly executes or implements an effect.

In biology, an effector is typically a muscle or gland that carries out actions such as contraction or secretion in response to signals from the nervous system or hormones. In physiology, effector organs form part of reflexes and regulatory pathways. In immunology, effector cells are immune cells that actively respond to antigens, including effector T cells that destroy infected cells and effector B cells that secrete antibodies.

In neuroscience, efferent pathways transmit signals from the central nervous system to effectors like muscles and glands, completing motor or autonomic responses.

In microbiology and cell biology, an effector can refer to a molecule that mediates the outcome of a signaling cascade, such as an enzyme, channel, or transcription factor that executes the cell’s response. Many pathogens also deploy effector proteins into host cells to subvert defenses or modify physiology, delivered by secretion systems such as type III or type IV.

In engineering and control theory, an effector (often called an actuator) is a device that converts a control signal into physical action, such as moving a valve, starting a motor, or adjusting a sensor. The term emphasizes the translation of information into action.