In PV, it has been shown that B cells function as antigen-presenting cells stimulating Dsg3-specific CD4+ T helper (Th) cells to secrete cytokines such as interleukin (IL)-4, IL-6 and IL-10 which are required for proliferation of memory B cells and differentiation into antibody-producing plasma cells [49-51]. The gene discussed is CD4; the disease is acquired polycythemia vera.