Immunization with the Sm nuclear antigen induces anti-Sm antibodies in normal and MRL mice

The spontaneous occurrence of antibodies against the Sm nuclear antigen is a highly specific marker for the diagnosis of SLE. We have previously shown that anti-Sm can be elicited by immunization of SLE-prone mice with purified Sm antigen. In the present study, this autoantibody was induced in normal mice by a similar immunization protocol. Anti-Sm produced by normal strains was predominantly IgG1, which is similar to the isotype distribution in Sm-immunized MRL mice, but unlike the IgG2a-dominated response seen for spontaneous anti-Sm. Anti-Sm raised by immunization in most strains recognized epitopes not seen by spontaneous human and murine SLE anti-Sm; of the eleven normal strains tested, only C3H and AKR, strains from which MRL was partially derived, responded to these determinants. Further, immunoblot analysis of anti-Sm generated by immunization of MRL and normal mice revealed that the same proteins recognized by spontaneous human and murine anti-Sm were also seen by these sera. This study shows that an autoantibody highly characteristic of SLE can be produced in normal and MRL mice after appropriate immunization, and that the fine specificity of such experimentally induced antibody can be similar to that of spontaneous anti-Sm autoantibodies. The results imply a role for autoimmunization with Sm in the production of anti-Sm.