T cell responses are governed by avidity and costimulatory thresholds

Abstract

This study analysed avidity and costimulatory requirements for the activation of T cells in vivo and in vitro. The avidity of the T cell/APC interaction was varied by using altered peptide ligands for stimulation. Costimulatory requirements were studied using T cells from CD28-deficient mice. The experiments indicate that T cell activation is not an all or none event but occurs in distinct steps. For each step a certain avidity and/or costimulatory threshold has to be met. Dependent upon the avidity of the interaction and the presence of costimulation, T cells may undergo blast formation alone or proliferate or eventually both proliferate and differentiate to effector cells. Thus, T cell activation is governed by avidity and costimulatory thresholds.