Plants have PRRs (pattern recognition receptors) that allow them to recognize PAMPs and MAMPs (pathogen- and microbial-associated molecular patterns). This recognition can activate PTI (PAMP-triggered immunity), which attempts to halt colonization by the pathogen. In addition, plants have NB-LRR (nucleotide binding-leucine rich repeat) proteins that recognize pathogen effectors, which results in ETI (effector-triggered immunity). Antimicrobial chemicals and enzymes are also produced by plants as secondary metabolites.