MPs contain numerous proteins and lipids similar to those present in the cell membranes from which they originate. Furthermore, as MPs' membranes engulf some cytoplasm during membrane blebbing, they may also contain proteins derived from it, mRNA, and, as recently demonstrated, microRNA (miRNA) [44] . It is now emerging that miRNAs may play a key role in host defence and inflammation [45, 46] . Moreover, MPs may "hijack" infectious particles (e.g. human immuno deficiency virus (HIV) or prions) from the cytoplasm or possibly even whole intact organelles such as the mitochondria [42] .