1. Introduction
The innate immune system act as the first line of defense against
bacterial infections, and its disorder results in the development of
infectious, inflammatory and autoimmune diseases. Pattern recognition
receptors (PRRs) are expressed outside or inside of innate immune cells,
which can recognize pathogen-associated molecular patterns (PAMPs)
conserved in different pathogens and trigger specific signaling pathways
that regulate early host responses. Currently known types of PRRs
include Toll-like receptors (TLRs) and C-type lectin receptors (CLRs)
located on cell membrane, NOD-like receptors (NLRs), RIG-I-like
receptors (RLRs) and AIM2-like receptors (ALRs) expressed in the
cytoplasm[1,2]. Wherein the nucleotide-binding oligomerization
domain 2 (NOD2) represents a well-characterized PRR of the NLR family
that recognizes muramyl dipeptide (MDP) , activating signaling pathways
and promoting cytokine expression[3]. Studies have shown that NOD2
plays an important role in the process of antimicrobial infection, and
polymorphisms in coding genes of NOD2 are associated with susceptibility
to leprosy and Crohn’s disease (CD)[4,5]. Since the discovery of
NOD2, studies have provided insights into the structure of NOD2,
signaling pathways regulated by NOD2 and roles of NOD2 in infection and
maintenance of tissue environmental homeostasis, etc. In this review, we
summarize the current information on the function and regulation of NOD2
in infectious diseases.