Table 1.

List of four major sub-families of Pattern Recognition Receptors (PRRs).

PRRs	Role	Ref
Cytoplasmic Retinoic acid-inducible gene I (RIG-I) like receptors (RLRs)	Key components for pathogenic RNA recognition and modulate an antiviral immune response.	[5,6]
Cytosolic nucleotide-binding oligomerization domain (NOD)- Leucine Rich Repeats (LRR)-containing receptors (NLR)	Regulation of inflammasome reaction and cytokine production.	[7,8]
Toll-like receptors (TLRs)	Represent an essential innate immune sensor, can be largely classified into two categories. Cell surface TLRs: mainly recognize microbial membrane components such as proteins, lipoproteins, and lipids; Endosomal TLRs: mainly recognize pathogen-derived nucleic acids.	[9,10]
C-type lectin-like receptors (CLRs)	Expressed on DCs and have a key role in orchestrating the stimulation of signaling pathways that regulate adaptive immune responses.	[11]