Over the past 30 years, prenatal corticosteroid treatment, called betamethasone has been administered to thousands of women at risk of premature birth to accelerate fetal lung maturation in the preterm neonates. However, the long term effects have not been analyzed in detail, especially the possible effects on the immune system. Given the importance of T cells in adaptive immune responses, we hypothesise that prenatal steroid treatment impairs the normal development of the offspring’s immune system and therefore increases the risk for autoreactivity/allergy later in life.The main focus of our project is to study T cell development and long-term effects on the immune system in offspring whose mothers were treated with prenatal corticosteroids. To test our hypothesis we plan to apply our model of autoimmunity and allergy, and to analyse in detail the immune system at birth and later in life of children whose mothers received steroids.