![]() These responses cause recruitment of more innate immune cells to the site of infection leading to their activation, migration of activated antigen presenting DCs to draining lymph nodes to prime lymphocytes, and ultimately to the elimination of the pathogen or control of the pathogen until the adaptive immune response is enabled. Moreover, microbial pathogens are usually composed of several PAMPs and activate multiple PRRs on innate immune cells that act in concert leading to the activation of downstream signaling events and the secretion of inflammatory cytokines, chemokines, and antimicrobial peptides. Thus, the different cellular locations of the PRRs make it possible for the innate immune system to respond to both cell-invasive and non-invasive pathogens. ![]() Of these, the best characterized sensors are several families of pattern recognition receptors (PRR) that detect invariant features of invading classes of microbes known as pathogen associated molecular patterns (PAMP) that include Toll-like receptors (TLRs), membrane-bound C-type lectin receptors (CLRs), cytoplasmic nucleotide-binding oligomerization domain (NOD) leucine-rich-repeat containing receptors (NLRs), and cytoplasmic retinoic acid-inducible gene 1 protein (RIG-1) helicase receptors. ![]() ![]() To identify microbial invaders and to mount an appropriate inflammatory response, the innate immune system has evolved an elaborate system of pathogen and commensal microbial sensors in the form of germline encoded host cell receptors and their associated signaling pathways. ![]() Cells of the innate or natural immune system such as neutrophils, macrophages, dendritic cells (DC), natural killer cells (NK), eosinophils, basophils, and mast cells form the first line of defense to protect the host against microbial invaders and parasites. ![]()
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