Major pattern recognition receptors (PRRs): Cell associated*

PRR	Recognize	Functions
Plasma membrane-bound
TLRs 1, 2, 4, 5, 6	Variety of microbial PAMPs and tissue-derived DAMPs	Cytokine release, activation of immune cells
Macrophage scavenger receptor	Gram-negative and gram-positive bacteria	Cytokine release, activation of immune cells
Macrophage mannose receptor	Microbial mannan	Opsonization of bacteria, fungi
Dectin 1 and 2	Fungal beta-glucan	Opsonization of bacteria, fungi
Formyl peptide receptor	Bacterial membrane N-formylmethionine	Opsonization and microbial lysis
Intracellular (cytoplasmic or endolysosomal)
TLRs 3, 7, 8, 9, 10	Variety of microbial PAMPs	Cytokine release, activation of immune cells
NLRs (NOD1 and 2)	Bacterial cell wall peptidoglycan, MDP	Cytokine release, immune cell activation
RLRs (RIG-1)	Viral dsRNA	Clearance of RNA and DNA viruses
MDA5	Viral dsRNA	Clearance of RNA viruses
LGP2	Viral RNA	Clearance of RNA viruses

Additional plasma membrane receptors that typically do not react directly with microbes but play an important role in innate host defense are the complement receptors that bind activated (cleaved) C3 (C3b and C3bi), which mediate opsonization, and the macrophage receptor for phosphatidyl serine, which aids recovery from inflammation by removing apoptotic cells. Complement receptor 3 (CR3) can bind beta-glucan in the fungal cell wall at a site distinct from its complement-binding site, but the biologic significance of this binding is not proven.

PRR: pattern recognition receptor; TLR: Toll-like receptor; PAMP: pathogen-associated molecular pattern; DAMP: damage-associated molecular pattern; NLR: NOD-like receptor; NOD: nucleotide-binding oligomerization domain; MDP: muramyl dipeptide; RLR: RIG-1-like receptor; RIG-1: retinoic acid-inducible gene 1; dsRNA: double-stranded ribonucleic acid; MDA5: melanoma differentiation-associated gene 5; LGP2: laboratory of genetics and physiology 2.

* This table includes major examples but is not exhaustive.

Original figure modified for this publication. Reproduced from: Liu AH, Zasloff MA, Johnston RB Jr. Innate immunity. In: Middleton's Allergy: Principles and Practice, 7th ed, Adkinson NF Jr, Busse WW, Bochner BS, et al (Eds), Elsevier 2008. Illustration used with the permission of Elsevier, Inc. All rights reserved.

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Major pattern recognition receptors (PRRs): Cell associated*