53 PU.1 Expression Delineates Heterogeneity in Primary Th2 Cells

Primary T helper 2 cells are heterogeneous in nature, expressing subsets of cytokines at varying levels. Mechanisms controlling this spectrum of phenotype are still unclear. The ETS-family transcription factor PU.1 is a critical regulator in hematopoiesis. PU.1-null mice are either embryonic or neonatal lethal, and all result in defective lymphoid and myeloid lineage development. We identified selective expression of PU.1 in Th2 but not Th1 subsets. Th2 cytokine production is decreased in cultures transduced with a PU.1 expressing retrovirus and increased in Th2 cells expressing a short hairpin RNA that decreases PU.1 expression. In primary cultures, PU.1 expression is restricted to a subpopulation of Th2 cells that express CCL22 but decreased level of other Th2 cytokines. We also defined that the PU.1 transactivation and PEST domains are not required for regulating Th2 cytokine production. PU.1 appears to regulate the Th2 phenotype by antagonizing GATA-3 function by interfering with GATA-3 DNA binding both in vitro and in vivo without altering protein levels. Expression of PU.1 in Th2 cells alters cytokine production and may contribute towards establishing the spectrum of cytokine production observed in Th2 populations. These findings will be important in understanding the development of Th2-mediated diseases such as asthma and atopic dermatitis.