This 2019 Dutch/German/Romanian perspective aimed for a better understanding of immune systems:

“Based on molecular, immunological, and evolutionary arguments, we propose that innate immune memory is a primitive form of immune memory present in all living organisms, while adaptive immune memory is an advanced form of immune memory representing an evolutionary innovation in vertebrates.

Innate immune responses have the capacity to be trained, and thereby exert a new type of immunological memory upon reinfection. The central feature of trained innate immune cells is their ability to mount a qualitatively and quantitatively different transcriptional response when challenged with microbes or danger signals. Evidence supports convergence of multiple regulatory layers for mediating innate immune memory, including changes in chromatin organization, DNA methylation, and probably non-coding RNAs such as microRNAs and/or long non-coding RNAs.

Two properties of adaptive immune response are mediated by two fundamentally different types of mechanisms:

1. Higher magnitude and speed of the response is mediated by epigenetic programming.
2. Specificity of the response is insured by gene recombination of TCR [T cell receptor] and BCR [B cell receptor] and clonal expansion of specific cell subpopulations upon antigen recognition.

To be effective, highly specific immune response requires huge diversity of receptors and antibodies, which is achieved by somatic rearrangement of gene segments. Recombination results in millions of TCR and antibody variants able to recognize and neutralize millions of various antigens.“

This paper included speculations such as “Evidence supports..probably non-coding RNAs” quoted above, and the penultimate sentence:

“One can envision that vaccines that are capable of inducing both forms of immune memory at the same time would be more effective.”

100% factual evidence is preferred. Overall information can only be as accurate as the least accurate information.

This review highlighted a goal for humans to have both a functional innate immune system and a functional adaptive immune system. The lead author coauthored A dietary supplement that trains the innate immune system and a study referenced in Eat your oats.

https://www.sciencedirect.com/science/article/pii/S1931312818306334 “Innate and Adaptive Immune Memory: an Evolutionary Continuum in the Host’s Response to Pathogens” (not freely available)