Since elevated counts of activated Teffector cells as well as reduced numbers and functional properties of Treg are a known feature of active SLE, it was not surprising that we found (in accordance with disease severity) increased frequencies of CD4+CD25+ Teffector cells and an increased ratio of Teffector/Treg cells in PIL+/+ mice compared to less active PIL-/- knockout mice or controls [1, 8]. Here, CD4 is linked to systemic lupus erythematosus.