Extracellular vesicles induced by intravenously administered syngeneic red blood cells modulate macrophage phagocytic activity in mouse humoral immunity

Aim: Phagocytosing macrophages are involved in the induction of humoral immunity to corpuscular antigens. Recently, we demonstrated that B cell response to haptenated sheep red blood cells (SRBC) could be suppressed by extracellular vesicles (EVs) produced by suppressor T cells activated through intravenous administration of a high dose of syngeneic mouse red blood cells (sMRBC). However, the mechanism underlying the inhibitory effect of sMRBC-induced EVs on macrophages involved in activation of humoral immunity remained unclear. Thus, the current studies aimed at investigating the phagocytic and antigen-presenting activity of macrophages treated with sMRBC-induced EVs. Material/Methods: Mouse thioglycollate-induced peritoneal macrophages were treated with sMRBC-induced EVs and then pulsed with either native or fluorescein isothiocyanate-conjugated SRBC. Afterwards, macrophages were, respectively, administered intraperitoneally into naive recipients or subjected to flow cytometric analysis. The elicited humoral immune response was evaluated in plaque forming and haemagglutination assays. Results: Decreased number of B cells secreting SRBC-specific antibodies was shown in spleens of mouse recipients of SRBC-pulsed macrophages pretreated with sMRBC-induced EVs along with an increased ratio of IgM to IgG serum antibodies. Furthermore, pretreatment of macrophages with sMRBC-induced EVs reduced their phagocytic activity and expression of costimulatory molecules involved in antigen phagocytosis and presentation. Conclusions: Current research findings demonstrated the impaired ability of macrophages to activate B cells due to the action of sMRBC-induced EVs, which may play a role in suppressing self-reactive B cells. Thus, our results seem to have translational potential in development of therapeutic strategies to prevent the macrophage-induced humoral immunity against nonpathogenic antigens.