These particles are taken up by many elements of the immune system, including the microglia – however, their size comparable to viruses, makes them less likely to cross the BBB, supposedly intact in MWoA [39] and MWA [40], although increased levels of matrix metalloproteinase-9 (MMP-9) have been associated with migraine [41, 42]. This evidence concerns the gene MMP9 and migraine disorder.