A protein that recognizes the pattern of certain molecules on the surface of invading pathogens, such as bacteria, fungi, or viruses, and binds to them, thereby eliciting an immune response by the host organism. Such receptors occur in both plants and animals, and may be membrane bound or present in plasma or other body fluids. The molecules recognized by them are called pathogen-associated molecular patterns (PAMPs). An example is the spatial arrangement of mannose or fucose molecules on bacterial surfaces that matches the recognition sites on mannose-binding lectin, a PRR found in plasma. Coating by this lectin makes the bacterium more susceptible to phagocytosis. See also immunity.