T helper cells play a distinct role in activating and regulating immune responses. Th1 cells mediate cellular immunity by activating macrophages, whereas Th2 cells mediate Immoral immunity by activating B cells. The differentiation of Th1 and Th2 cells accompany drastic changes in immune function, cellular metabolism, gene expression, chromatin structure, and cell morphology. To search for more information on the immune functions of Th1 and Th2 cells, we examined a gene expression profile in immune related genes by microarray analysis. As expected many differentiation-specific cytokine, chemokine, and transcription factor genes are differentially expressed. I also discovered that a group of interferon-regulated genes is selectively expressed in Th1 cells, and that a group of immunoglobulin genes and various types of cell surface receptors are selectively expressed in Th2 cells. These studies extend the current understanding of immune function of T helper cells and rind more molecules involved in the T helper cell differentiation.