keep in mind this is not proven but is a promising angle, CRSPR as made popular is a hijacked mechanism used to edit DNA sequences. normally this mechanism is used in prokaryotic organisms as an immune system. there are tags in the prokaryotes DNA that are used to match with foriegn DNA and signal it for destruction.

this type of arrangement MAY, possibly exist in eukaryotes as well and may be the basis of self/nonself recognition.

i have yet to talk to anyone else in professional context, this is inference on my part but it the best answer i can suggest for now.

you would want to look at antigen presentation and antibody production mechanisms, in deep detail .