Serum exosomes in pregnancy-associated immune modulation and neuroprotection during CNS autoimmunity

•Pregnancy results in suppression of established EAE.•Serum exosomes contribute to the pregnancy-induced suppression of EAE.•Pregnancy exosomes facilitate OPC migration into CNS lesions.

In multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), relapses are markedly reduced during pregnancy. Exosomes are lipid-bound vesicles and are more abundant in the serum during pregnancy. Using murine EAE, we demonstrate that serum exosomes suppress T cell activation, promote the maturation of oligodendrocyte precursor cells (OPC), and pregnancy exosomes facilitate OPC migration into active CNS lesions. However, exosomes derived from both pregnant and non-pregnant mice reduced the severity of established EAE. Thus, during pregnancy, serum exosomes modulate the immune and central nervous systems and contribute to pregnancy-associated suppression of EAE.