In a nutshell, what we mostly study is the release from cells of small membrane structures known as exosomes. We were at a conference on this topic, and one researcher who studies the contents of blood borne exosomes kept finding an RNA sequence that didn't match any known human sequence (in about 60-70% of samples). He did some investigating and found that the sequence belonged to a cow gene called epidermal growth factor receptor (which is a gene humans have a homolog for, and is important in cellular growth and cancer biology). What was unclear was whether the cow DNA was absorbed and transcribed by the human machinery, or whether the cow exosomes were being somehow absorbed into the blood stream. My suspicion is that it's most likely the latter. Either way it's quite curious.

The copy numbers were miniscule, so who knows if there is any biologic function associated with the gene, but it's interesting that it was always this one gene and always from cow (chicken and pork also have EGFR, for example, but they weren't detected). This wasn't actually the main point of his talk, but it was the most fascinating part to me.

Please let me know if I can answer any questions more specifically, as I am happy to.