Multiple sclerosis (MS) is thought to be T cell mediated but the mechanisms eliciting such a dysregulated adaptative immune response remain enigmatic.

To examine the activation profile of antigen-presenting cells (APCs) in MS.

A total of 98 study subjects were enrolled including patients suffering from relapsing–remitting, secondary- and primary-progressive (PP) MS, other inflammatory neurological diseases, and healthy controls. Blood monocytes and B cells were stimulated using specific ligands of toll-like receptors (TLRs) or inflammasomes or Epstein–Barr virus (EBV) particles. Their activation profile was determined before or after stimulation by flow cytometry (CD40, CD80, CD83, CD86, and human leukocyte antigen–antigen D related (HLA-DR)) and Luminex assay, measuring the concentration of eight cytokines in culture supernatants. Differences among groups were assessed in a linear model framework.

We demonstrate that relapsing MS patients exhibit an increased expression of HLA-DR and CD40 ex vivo, mostly at the surface of B cells. Specific stimulations of TLR or inflammasomes enhance the expression of components of the immunological synapse and the cytokine secretion but without differences between categories of study subjects.

These data suggest that the activation profile of B cells is increased in MS. However, the perception of the danger signal by B lymphocytes and monocytes does not seem to be different in MS patients as compared to control subjects.