As our results had demonstrated that AR production was not limited to a pre-committed subset of T cells, we then tested whether AR production was regulated by acute signals in the immediate milieu during TCR stimulation. In many cell types AR is strongly regulated by the cAMP-PKA-CREB signaling pathway. AR expression was significantly up-regulated by cAMP-elevating agents in both resting and anti-CD3 stimulated human PBMC populations enriched for human T cells [40] . However, in that study the negatively-selected T cell population would also have contained basophils, and we have shown that basophils express AR rapidly in response to IL-3 and cAMP agonist ( [31] and unpublished data). Thus anti-CD3 stimulation of the CD4 T cell + basophil population could have induced IL-3 production by T cells, indirectly resulting in AR production by basophils. We have now re-examined the effect of cAMP elevation on the expression of AR by different T cell subsets.