The major function of immunoglobulins (Igs) that is widely known is recognition and binding of specific antigens. In addition to this, they have other biological functions such as activation of complement, aggregation of platelets, and degranulation of basophils and mast cells. A new function of Ig was detected in an autoimmune mouse model, the induction of growth factor (s) from the FDC-P2/l85-4 cell line and stimulation of cell proliferation via an autocrine mechanism. Such a function of immunoglobulins might play an important role in the pathogenesis of autoimmune diseases.