Table 2.

Classification of the Identified Types of NOD-Like Receptors (NLRs) and Their Main Activators

NLR	Main Activators
NLR A
CIITA	IFN-γ
NLR B
NAIP1/2	Injectisome
NAIP5/6	Flagellin
NLR C
NOD1 (NLRC1)	Peptidoglycan iE-DAP
NOD2 (NLRC2)	Peptidoglycan Muramyl dipeptide ssRNA
NLRC3	Undetermined
IPAF (NLRC4)	Injectisome/flagellin (mediated by NAIPs)
NLRC5	IFNγ LPS Poly I:C
NLRX1	LPS Viral RNA
NLRP
NLRP1	Anthrax lethal toxin Toxoplasma gondii ATP depletion Muramyl dipeptide
NLRP2	LPS/TNF-α
NLRP3	K+ efflux Bacterial toxins and RNA Nigericin Aluminum hydroxide ATP Cholesterol and uric acid crystals Particulate matter Mitochondrial damage
NLRP4	Viral DNA/RNA
NLRP5/8/13/14	Undetermined
NLRP6	Viral RNA TLR ligands Lipotheicoic acid
NLRP7	Bacterial acylated lipoproteins Lysosomal proteases? K+ flux?
NLRP9	dsRNA
NLRP10	NOD1 activation
NLRP11	TLR4 ligands
NLRP12	ATP TLR2 ligands Yersinia pestis

ATP = adenosine triphosphate; CIITA = major histocompatibility complex class II transactivator; iE-DAP = γ-D-glutamyl-meso-diaminopimelic acid; IFN = interferon; K = potassium; IPAF = interleukin-1b (IL-1b)-converting enzyme-protease-activating factor; LPS = lipopolysaccharide; NLR = nucleotide-binding oligomerization domain-like receptors; NAIP = Baculoviral IAP repeat-containing protein 1; NLRP = nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain-containing receptor; NOD1 = Nucleotide-binding oligomerization domain-containing protein 1; TNF = tumor necrosis factor; other abbreviations as in Table 1.