Lack of high avidity IgM anti-ssDNA antibodies in cells from autoimmune-prone and autoimmune mice

Non-autoimmune prone CBA mice were compared with autoimmune prone NZB, NZW, and (NZB × NZW)F₁ mice for the ability of their splenic cells to produce anti-ssDNA-forming cells spontaneously in vitro, measured in the plaque forming cell assay. The number of antibody forming cells was measured and the relative avidity of antibody produced determined using a plaque inhibition assay. Splenic lymphocytes from young animals of a non-autoimmune strain (CBAIJ) were shown to be capable of generating anti-ssDNA IgM antibody-forming cells in culture which displayed a higher avidity for antigen than that from autoimmune-prone or frankly autoimmune mice. Since an increased switching from IgM to IgG autoantibody production and defects in Fc-mediated signalling by IgG antibody have been identified in autoimmunity, we suggest that the metabolic block, normally in force in non-autoimmune-prone animals, accounts for this elevated avidity of IgM autoantibody.