Pam3CSK4 Induces B Cells to Release FasL+ Killer Exosomes That Suppress Allergic Asthma

Abstract

Abstract We have previously shown that mouse B lymphocytes can express Fas ligand (FasL) on their cell surfaces and can kill peptide antigen-specific T helper cells. In humans, FasL protein produced by human B cells was exclusively found intracellularly on the surface of exosomes. In the current study we determined that mouse B cells are a major source of FasL+ exosomes, as well as contributing significantly to the Granzme B+ exosome pool. The major B cell subsets in the spleen and lungs that produced FasL and Granzyme B were marked by CD9 and/or CD107a expression. We tested a panel of toll-like receptor ligands in combination with anti-IgM and CD40 ligand for their ability to activate killer function in purified mouse B cells. The TLR2 ligand Pam3CSK4 was a potent inducer of surface FasL expression and FasL+ exosome release from B cells. Using a mouse model of OVA-specific allergic airways disease, we showed that transfer of Pam3CSK4-induced B cell-derived exosomes diminished total numbers of eosinophils and CD4+ T cells in the bronchoalveolar lavage fluid (BAL). Lung TH cell apoptosis was higher in the mice that received exosome transfer. Lung cells produced less IL-4 and IL-5 upon restimulation with OVA in the exosome-treated mice. Effects of Pam3CSK4-induced exosomes on BAL cell infiltration, TH cell apoptosis and cytokine production were all diminished when exosomes were derived from mice with a functional mutation of the FasL gene. These data indicate a potential role for B cell-derived killer exosomes in control of allergic airways disease.