The immune system defends hosts against internal and external biologic threats. It also records an antigenic map of the environment such that it can appropriately respond to stimuli as benign or threatening.
A lesser-known function of the immune system may be to sample the microbiome for potentially beneficial traits it can add to the host inventory. Rather than executing wholesale destruction of pathogens, the host can benefit by domesticating invading organisms or parts thereof. The function can be summed in the word “xenovation”, innovation achieved through the selection and integration of foreign traits. Implications for biologic evolution, meme evolution, and computing evolution are discussed.
Components of pathogens can be processed and rendered benign or useful through various mechanisms. A historical example of this phenomenon is the domestication of one prokaryote (or at least its energetic machinery) by another to form a eukaryote. A current example is the processing of pathogen antigens for surface redisplay to other players in the immune system. The ability to protect against reinfection is a trait acquired via the pathogen. It is intuitively appealing to speculate that the immune system is in a perpetual state of exploration for innovative traits through domestication.
The exact mechanisms by which immune cells domesticate microbial traits remain to be elucidated. How sequences associated with those traits might end up in the germline also remains to be investigated.