Recently, using the flow cytometry, it has been demonstrated that the combination of pro-inflammatory interleukin-21 (IL-21) and B-cell receptor (BCR) stimulation enabled B cells to produce/secrete the active form of the cytotoxic serine protease granzyme B (GrB), which might exacerbate the MS progression (Niland et al., 2010; Bulati et al., 2014). Here, IL21 is linked to myeloid sarcoma.