An effective immune response requires the engagement of host receptors by pathogen-derived molecules and the stimulation of an appropriate cellular response. Therefore, a crucial factor in our ability to control an infection is the accessibility of our immune cells to the foreign material. Exosomes-which are extracellular vesicles that function in intercellular communication-may play a key role in the dissemination of pathogen- as well as host-derived molecules during infection. In this review, the authors highlight the composition and function of exosomes and other extracellular vesicles produced during viral, parasitic, fungal and bacterial infections and describe how these vesicles could function to either promote or inhibit host immunity.
Modulation of host immunity by exosomes during a viral or parasitic infection
Virus or parasite-infected cells, or the parasites themselves, release exosomes or microvesicles that can stimulate T-cell activation by providing antigens to APCs. In contrast, exosomes containing microbial molecules, such as HIV Nef or Leishmania GP63, can block T-cell activation or induce the apoptosis of immune effector cells. Extracellular vesicles released from virus-or parasite-infected cells can modulate both the innate and acquired immune response. In some cases, this is to the benefit of the pathogen, whereas in others, this is to the benefit of the host. Dashed lines indicate unknown mechanisms. See Glossary for definitions.