Activin A stimulates mouse macrophages to express APRIL via the Smad3 and ERK/CREB pathways

► APRIL is known to enhance Ig class switching such as IgA isotype. ► In this report, we found that activin A, through Smad3 and ERK/CREB, can stimulate Mϕs to express APRIL. ► Our results raise the possibility that activin A can indirectly modulate B cells via induction of APRIL in MALT Mϕs.