We reported previously that microRNA (miRNA) are present in whey fractions of human breast milk, bovine milk, and rat milk.
…In the current study, we used bovine raw milk and total RNA purified from exosomes (prepared by ultracentrifugation) and ultracentrifuged supernatants, and analyzed them using miRNA and mRNA microarrays to clarify which miRNA and mRNA species are present in exosomes, and which species exist in other forms.
…These results suggest that bovine milk exosomes might have effects in human cells by containing RNA.
Exocytosis is a normal cellular function, and is one way cells can communicate with each other or provide additional benefits to another. The picture in the wikipedia image shows exocytosis occurring between two neurons, but the process is by no means exclusive to this cell type. Basically, cells can form exosomes, or membrane-bound vesicles which are released from the cell. These can contain proteins, DNA, RNA, you name it.
It’s been known for a while that human milk also contains species of mRNA (messenger RNA) and miRNA (micro RNA). This study essentially says they’re also found in bovine milk. Moreover, they’re primarily located within exosomes when the milk is fractionated. Some of the miRNAs they found in the top 10 are actually shared in both human and pig milk and are predicted to regulate both carbohydrate and lipid metabolism. There are also species-specific miRNAs present in the exosomes, whose function is unknown (as is the majority of the RNA found).
They predict, due to the stability and acid-resistant characteristics of these RNA species, that they may serve a biological function, but they don’t know for sure. They found that a human macrophage-like cell line (an innate immune cell type) can take up these exosomes, but they don’t know if other cell types can as well. So basically, cow milk has all these RNA-containing exosomes floating around in it (much like human milk), and some of them are taken up by our cells. Biological functions still unknown.
Cells can release tiny packets of genetic material which can be taken up by other cells. The authors of this study found that cow milk contains these packets of material. In fact, some of this material is also found in other species, like humans and pigs. This material is super resilient, and so may serve some function, but we don’t know what! Also, some of our immune cells can take up these packets of material. We still don’t know what it does though.