The present invention relates to methods and compositions for the treatment and diagnosis of immune disorders, especially T helper lymphocyte-related disorders. In particular, the invention describes a gene known in the art, alternatively, as ST2, T1 and Fit-1, and referred to herein as the 103 gene. The 103 gene is disclosed herein to be differentially expressed in TH2 cells and not in TH1 cells. Further, the 103 gene product is demonstrated herein to be an important modulator of TH2 and TH2-like immune response both in vitro and in vivo. Thus, the 103 gene, its gene products and antibodies that specifically bind thereto can be used diagnostically or as targets for therapeutic intervention in the treatment of a variety of immune disorders.In this regard, the invention provides methods for the identification and therapeutic use of compounds for treatments of immune disorders, especially TH cell subpopulation-related disorders and including TH2 and TH2-like disorders (i.e., disorders associated with a TH2 or TH2-like mediated immune response) such as atopic conditions (e.g., allergy and asthma). Additionally, methods are provided for the diagnostic evaluation and prognosis of TH cell subpopulation related disorders, for the identification of subjects exhibiting a predisposition to such conditions, for monitoring patients undergoing clinical evaluation for the treatment of such disorders and for monitoring the efficacy of compounds used in clinical trials.