Antibodies of this type are present in the serum of normal individuals and are often polyreactive IgMs capable of binding to a variety of structurally unrelated, self and non-self antigens (Lacroix-Desmazes et al., 1998) . Such antibodies may represent a primordial form of the immune system that evolved to perform largely physiological functions rather than classical immune functions (Bouvet and Dighiero, 1998; Stewart, 1992) . One of these nonimmunological functions may be to promote tissue repair, serving effectively as trophic factors for specific cell types (Bieber et al., 2001) .