The innate immune system is the first aspect of the immune response to engage a pathogen.
The innate immune system protects the host during the time between microbe exposure and initial adaptive responses.
The innate immune response is evolutionarily ancient, found in all multicellular organisms, and expressed in humans as conserved elements (homologs) shared with other vertebrates and, in some form, with insects, plants, fungi, and bacteria.1
Components of the innate immune system include those of the host itself and also it sresident microbes, the microbiome.