In contrast, immunization of S100a9+/+, S100a9+/- and S100a9-/- female NZBWF1 mice resulted in similar levels of NP-specific antibodies between the strains (Figure 2B), suggesting a sex-specific effect of S100a9 in NZBWF1 lupus-prone mice. The gene discussed is S100A9; the disease is systemic lupus erythematosus.