CD4+CD25high nTregs are the major subset of T-cells that maintain immune tolerance.Breaking self-tolerance results in autoimmunity.This book gives you a simplified review about the immune tolerance and when it is failed resulting in autoimmune diseases using SLE and JRA as examples. In addition, a chapter of possible therapeutic modalities of nTregs is included. The practial part of the book was a study of the percentages of CD4+CD25high nTregs in the peripheral blood using flowcytometry for 40 children and adolescents with pediatric SLE and JRA in addition to 20 healthy subjects as a control group. The study demonstrated the relationship of nTregs to the disease status and corticosteroids. The variation of the percentage of nTregs with the age and duration of the disease in each group was as well emphasized. At the end of the book, we drew a conclusion and recommendations for further studies in this field.