Unrestrained Glycogen Synthase Kinase-3β Activity Leads to Activated T Cell Death and Can Be Inhibited by Natural Adjuvant

Abstract

Activated T cell death (ATCD) after peak clonal expansion is required for effective homeostasis of the immune system. Using a mouse model of T cell clonal expansion and contraction, we found that regulation of the proapoptotic kinase glycogen synthase kinase (GSK)-3β plays a decisive role in determining the extent to which T cells are eliminated after activation. Involvement of GSK-3β in ATCD was tested by measuring T cell survival after GSK-3β inhibition, either ex vivo with chemical and pharmacological inhibitors or in vivo by retroviral expression of a dominant-negative form of GSK-3. We also measured amounts of inactivating phosphorylation of GSK-3β (Ser9) in T cells primed in the presence or absence of LPS. Our results show that GSK-3β activity is required for ATCD and that its inhibition promoted T cell survival. Adjuvant treatment in vivo maintained GSK-3β (Ser9) phosphorylation in activated T cells, whereas with adjuvant-free stimulation it peaked and then decayed as the cells became susceptible to ATCD. We conclude that the duration of GSK-3β inactivation determines activated T cell survival and that natural adjuvant stimulation decreases the severity of clonal contraction in part by keeping a critical proapoptotic regulatory factor, GSK-3β, inactivated.