CD5 and neoplasm: Such antibodies resemble the so called “natural antibodies”, that are indeed produced by CD5+ B lymphocytes and in healthy donors are mainly IgM involved in complement-dependent anti-bacterial responses; natural IgM antibodies recognizing sugars, including O-linked olygosaccharides, have been reported also in patients with solid tumors, where they contribute to clear tumor cells by apoptosis [28]–[31].