Exosome release by primary B cells.

Exosomes are subcellular nanoparticles derived from the endosomal pathway. It is now becoming clear that a potential major in vivo source of exosomes is the B cell. Although it has been widely assumed that exosome release is a constitutive activity of most cell types, recent work has emphasized the role of cellular activation in the release of exosomes from primary cells. Like other lymphocytes, B cells undergo extensive cellular physiologic changes during the process of differentiation into effector cells. One newly identified feature of this process is exosome synthesis, which is initiated following the receipt of activation signals, particularly T-cell "help" via CD40 and IL-4 signaling. B-cell-derived exosomes contain immunoglobulin, which traffics antigen bound by the surface B-cell receptor (BCR) into the endosomal/exosomal pathway and finally into the extracellular space. Exosomes have been implicated in viral transmission, cell signaling, and antigen presentation, as well as in the disposal of effete or defective cellular components. However, the possible targets of B-cell-derived exosomes remain unknown. This review focuses on the synthesis and release of exosomes derived from activated and malignant B cells and explores the possible functions of B-cell-derived exosomes in immune function.