Exosomes in Pathogen Infections: A Bridge to Deliver Molecules and Link Functions

Abstract

Exosomes are extracellular vesicles derived from cell endocytosis which act as transmitters between cells. They are composed of proteins, lipids, and RNAs through which they participate in cellular crosstalk. Consequently, they play an important role in health and disease. Our view is that exosomes exert a bidirectional regulatory effect on pathogen infections by delivering their content. First, exosomes containing proteins and RNAs derived from pathogens can promote infections in three ways: (1) mediating further infection by transmitting pathogen-related molecules; (2) participating in the immune escape of pathogens; and (3) inhibiting immune responses by favoring immune cell apoptosis. Second, exosomes play anti-infection roles through: (1) inhibiting pathogen proliferation and infection directly; (2) inducing immune responses such as those related to the function of monocyte-macrophages, NK cells, T cells, and B cells. We believe that exosomes act as "bridges" during pathogen infections through the mechanisms mentioned above. The purpose of this review is to describe present findings regarding exosomes and pathogen infections, and highlight their enormous potential in clinical diagnosis and treatment. We discuss two opposite aspects: infection and anti-infection, and we hypothesize a balance between them. At the same time, we elaborate on the role of exosomes in immune regulation.

Keywords: apoptosis; exosome; immune regulation; infection; pathogen; transmit carrier.

Figure 1

Exosomes mediate further infection. Exosomes mediate further infection through transferring pathogen-related molecules (pathogenic genes and proteins) or even the entire pathogens. Therefore, exosomes can be either directly infectious, alter nuclear gene expression, or mediate toxic reactions.

Figure 2

Exosome-mediated immune evasion pathways. Exosomes can package pathogens, modifying them or shutting down important immune effectors. The proteins vacuolar protein sorting 4 homolog B (VPS4B) and ALIX may mediate the spread of packaged pathogens. The protein serum resistance-associated protein (SRA) mediates the alteration of pathogens.

Figure 3

Exosomes and the induction of immune responses. Exosomes promote the differentiation of monocytes, can activate macrophage toll-like receptor (TLR) receptors and promote the cytokine response of macrophages. Exosomes can also promote the proliferation and cytokine response of T cells, as well as activate B and NK cells.

Figure 4

Exosomes in infection and anti-infection. Exosomes participate in both infection and anti-infection processes ranging from pathogen infection to the regulation of immune responses.