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Innate immunity, once overlooked, is now recognized as crucial in immunology. It serves as the first line of defense against infection in vertebrates and is the sole defense mechanism in invertebrates and plants. Innate immunity also plays a vital role in maintaining homeostasis, shaping the microbiota, and is involved in various diseases. The study of innate immunity has expanded our understanding of the immune system beyond vertebrates to include all metazoans, plants, and even prokaryotes.
The innate immune system in eukaryotes and bacteria (gut microbiota) is similar. It is part of the broad arsenal of defense systems.
For instance, immune components such as SAM domain and HD domain-containing protein 1 (SAMHD1), masterminds, and the cGAS-STING pathway have also been found in bacteria, whose function is to defend against phage attacks
The ability of the innate and adaptive immune systems to communicate is central to protective immune responses and the maintenance of host health. Myeloid cells of the innate immune system can sense microbial ligands, perturbations in cellular homeostasis, and virulence factors. This sensing allows them to relay distinct pathogen-specific information to naïve T cells in the form of pathogen-derived peptides and a unique cytokine milieu.
Microbial lipopolysaccharides, flagellins, peptidoglycans and other microbial associated molecular patterns (MAMPs) can regulate cell proliferation, mucosal barrier function and multiple cellular inflammatory pathways by activating the innate immune system
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Elinav et al. 2013
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Lewis et al. 2016