MPO and systemic lupus erythematosus: Among all silica-exposed mice, B6 had significantly lower levels of BALF autoAb than other strains, including less anti-DNA IgM than silica-exposed mice in each of the lupus strains, less anti-DNA IgG than silica-exposed MRL and BXSB, and less anti-MPO than exposed BXSB (Table 1).