Le système immunitaire à la naissance : entre l'apprentissage du soi et du non-soi

Abstract

Early differentiation of T-cell progenitors in the thymus can be followed by analysis of both the expression of various CD cell surface markers and the expression of rearranged genes that encode TcR and surface Ig receptors. Once they have expressed TcR, autoreactive thymocytes are deleted while thymocytes that can potentially recognize foreign antigens in association with self MHC molecules are positively selected. Most of these processes which result in self tolerance take place during the prenatal life. At birth, the immune system of human newborns is partially immature resulting in deficiency in secretion of lymphokines, cell-mediated cytolysis and Ig synthesis. One of the fundamental differences between adult and newborn immune functions resides in prior exposure to antigen or not. After birth, antigenic challenges are responsible for transient expression of immune functions. They also lead to further differentiation of lymphocytes towards an immunologic memory state. This state improves immune functions and results in protection against further infection by antigenically related pathogens. The identification of the molecular basis responsible for these functional changes is now in progress.