Figure 3.

Danger signals recognized by different pattern recognition receptor (PRRs). Each PRR recognizes a different danger signal. NOD-like receptor family pyrin domain-containing 1 (NLRP1) is activated by certain bacterial toxins. NOD-like receptor family caspase recruitment domain-containing 4 (NLRC4) works in combination with neuronal apoptosis inhibitory protein (NAIP), and the ligand itself binds to NAIP. NAIP recognizes the bacterial protein flagellin and the constituent proteins of the type III secretion system (T3SS) of Gram-negative bacteria and forms a complex with NLRC4. Absent in melanoma 2 (AIM2) directly recognizes double-stranded DNA and is considered to be activated during infection with double-stranded DNA viruses, such as cytomegalovirus, and cell-invasive bacteria, such as Francisella tularensis and Listeria monocytogenes. AIM2, absent in melanoma 2; DAMPs, danger-associated molecular patterns; T3SS/T4SS, type III/IV secretion system; PAMPs, pathogen-associated molecular patterns; PRR, pattern recognition receptor; NLRC4, NOD-like receptor family caspase recruitment domain-containing 4; NLRP1/NLRP3, NOD-like receptor family pyrin domain-containing 1/3; NAIP, neuronal apoptosis inhibitory protein.