The initial observation by Yilmaz et al. that lymphocyte deficient rag1−/− mice are protected from stroke (Yilmaz et al., 2006) could be extended to mice with severe combined immunodeficiency lacking T cells and B cells (Hurn et al., 2007) and to CD4+ and CD8+ T cell-deficient animals (Yilmaz et al., 2006). The gene discussed is CD4; the disease is stroke disorder.