Normal B-lymphocyte precursors undergo rearrangement of surface immunoglobulins (IgM, IgD), thus becoming naive B lymphocytes (CD5+) that circulate in the peripheral blood and are found in primary lymphoid follicles of lymphoid organs and in the mantle zone: most cases of mantle cell lymphoma correspond to CD5+ naive B cells. This evidence concerns the gene CD5 and mantle cell lymphoma.