BXSB.Yaa CD1-/- (BXSB.Yaa Cd1d1/Cd1d2-/-) mice are a BXSB-congenic strain carrying a null mutation of the CD1 antigen complex; both CD1.1 (Cd1d1) and CD1.2 (Cd1d2) expression is abolished. Homozygous (CD1-/-) mice are natural killer T cell (NKT)-deficient. Homozygous mice are viable and fertile. Both homozygous and heterozygous mice develop spontaneous lupus-like autoimmune syndrome similarly to BXSB/MpJ inbred mice (Stock No. 000740): mortality in males starts at ~13 weeks of age with 50% lethality by ~30 weeks and 76% lethality by ~40 weeks. Females develop a greatly attenuated form of autoimmune disease because they lack Yaa. BALB/c-congenic mice harboring this null mutation of the CD1 antigen complex are described and available from The Jackson Laboratory Repository as Stock No 003814.