SELL and progressive multifocal leukoencephalopathy: In example, beside its role in leucocytes migration, L-selectin (CD62L) has been suggested to play a central role in adaptive immune response by initiating lymphocyte recirculation through the lymph nodes (38), whereas in remitting, multiple sclerosis treated with natalizumab-reduced L-selectin (CD62L) expression in T cells in cryopreserved samples has been proposed as a biomarker of pre-PML (progressive multifocal leukoencephalopathy) state (58–60).