Our innate immune system distinguishes microbes from self by detecting conserved pathogen-associated molecular patterns. However, these are produced by all microbes, regardless of their pathogenic potential. To distinguish virulent microbes from those with lower disease-causing potential the innate immune system detects conserved pathogen-induced processes. ~ Dutch immunologist Marijke Keestra et al
Innate immune systems exist in all cells and organisms.
For a human with a healthy microbiome, resistance to infection is ever vigilant. Skin and cells that line entry passages deal with dirt, dust, and germs.
Commensal bacteria reside on the skin and in the mucous membranes of the eyes, nose, mouth, throat, and gastrointestinal tract. Their services include removing debris that makes a meal for a microbe, and warning of unwelcome foreigners.
There are various agents that recognize pathogens. Many are proteins but some RNA molecules also keep a lookout.
A widespread epigenetic process, RNA interference (RNAi) affects which genes are active and how active genes are. MicroRNA (miRNA) and small interfering RNA (siRNA) are active in the RNAi process.
RNAi acts as an innate antiviral defense in plants, fungi, and animals. There are also protein-based antiviral defenses. Numerous viruses have learned how to suppress these anti-viral agents.