CD27 and tropical spastic paraparesis: Flow cytometric analysis was able to differentiate B cell subpopulation into five subsets, including naïve (IgD+CD27-), unswitched memory (IgD+CD27+), double negative (IgD-CD27-), switched memory (IgD-CD27+) B cells and ASCs (IgD-CD27++) in CSF of a ND and a HAM/TSP patient (Fig 1B).