MOLECULAR REGULATION OF INTERLEUKIN-2 EXPRESSION BY CD28 CO-STIMULATION AND ANERGY

The consequences of T-cell receptor engagement (signal 1) are profound ly affected by the presence or absence of co-stimulation (signal 2). T -cell receptor (TCR) stimulation in the absence of CD28-mediated costi mulation not only results in little interleukin (IL)-2 production, but induces a long lasting hyporesponsive state known as T-cell clonal an ergy. The addition of CD28 ligation to signal 1, on the other hand, re sults in the production of copious amounts of IL-2. Our laboratory has utilized CD4(+) Th1 clones in an effort to understand the molecular e vents resulting in enhanced IL-2 production by co-stimulation and the inhibition of IL-2 production in energy. Our current studies have focu sed on defining the post-transcriptional effects of CD28-enhanced IL-2 production. The data suggest that a major component of CD28's ability to regulate IL-2 production occurs at the level of message stability and involves the 3'-untranslated region of the message. In terms of an ergy, our recent studies support the notion that it is not the result of TCR engagement in the absence of costimulation, but rather signal 1 in the absence of IL-2 receptor signaling and proliferation. Furtherm ore, T-cell anergy appears to be an active negative state in which IL- 2 production is inhibited both at the level of signal transduction and by cis-dominant repression at the level of the IL-2 promoter.