Recent evidence suggests that interleukin-17-producing CD4(+) T cells (Th17 cells) are the dominant pathogenic cellular component in autoimmune inflammatory diseases, including
multiple sclerosis. It has recently been demonstrated that
all-trans retinoic acid can suppress Th17 differentiation and promote the generation of Foxp3(+) regulatory T cells via
retinoic acid receptor signals. Here, we investigated the effects of
AM80, a synthetic
retinoid with enhanced
biological properties to
all-trans retinoic acid, on Th17 differentiation and function and evaluated its therapeutic potential in
experimental autoimmune encephalomyelitis (EAE), an animal model of
multiple sclerosis.
AM80 treatment was more effective than
all-trans retinoic acid in inhibiting Th17 differentiation in vitro.
Oral administration of
AM80 was protective for the early development of EAE and the down-modulation of Th17 differentiation and effector functions in vivo. Moreover,
AM80 inhibited
interleukin-17 production by splenic memory T cells, in vitro-differentiated Th17 cells, and central nervous system-infiltrating effector T cells. Accordingly,
AM80 was effective when administered therapeutically after the onset of EAE. Continuous
AM80 treatment, however, was ineffective at inhibiting late EAE symptoms despite the maintained suppression of
RORgammat and
interleukin-17 expression levels by central nervous system-infiltrating T cells. We reveal that continuous
AM80 treatment also led to the suppression of
interleukin-10 production by a distinct T cell subset that expressed both Foxp3 and
RORgammat. These findings suggest that
retinoid signaling regulates both inflammatory Th17 cells and Th17-like regulatory cells.