A, Considerable individual variation in the survival of BXSB. Yaa male mice, n = 93. Long term survival of 26 males carrying the C57BL/6 Y chromosome (B6Y) demonstrate the dependency of the autoimmune disease on Yaa. B, Longitudinal phenotyping of a cohort of BXSB.Yaa mice for ICOS+ CD4+ T cells. Each line represents data from FACS analysis of blood white blood cells from individual mice. Transition from stochastic to deterministic occurs at 6-8 weeks of age. Therapies applied at this point are predicted to have the potential of preventing this transition.