Natural antibodies against tubulin, actin myoglobin, thyroglobulin, fetuin, albumin and transferrin are present in normal human sera, and monoclonal immunoglobulins from multiple myeloma and Waldenström's macroglobulinemia may express similar antibody specificities.

Sera from a pool of 800 healthy donors and from 3 individual healthy donors were passed through tubulin, actin, thyroglobulin, myoglobin, fetuin, transferrin and albumin immunoadsorbents. Proteins were eluted in all the immunosorbents and were found to be essentially composed of the three major Ig classes and albumin. The isolated Ig fractions were shown to react specifically, via their Fab fragment with the antigens and were specifically inhibited by them. These results strongly suggest that natural antibodies against the seven antigens are present in normal human serum, and probably against a high variety of self antigens. These results prompted us to search in the sera of patients with monoclonal gammapathies, paraproteins having natural antibody-like function. Among the 62 sera studied 3 were shown to react with actin and 1 with tubulin. Most important, these 4 monoclonal immunoglobulins exhibited similar specificities to that found with natural antibodies. This seems to indicate, that at least for some patients, the monoclonal immunoglobulins produced may represent the expansion of a clone producing a natural antibody.