The expression of AR by both CD45RA-and CD45RA+ subsets of CD4 T cells was tested at the mRNA level in SEBstimulated cells sorted according to AR and CD45RA expression ( Figure 4C ). Confirming the specificity of the anti-AR antibody AR is produced by memory CD4 T cell subsets expressing different cytokine phenotypes. Although naive CD4 T cells are relatively homogeneous, the memory population includes a wide range of differentiated effector subsets. As AR is expressed selectively by mouse Th2 cells, we examined whether AR production by human CD4 memory T cells was preferentially associated with expression of a particular cytokine or surface marker pattern. Th1-and Th2-biased human CD4 T cell populations were induced by stimulation of sorted naive human CD4 T cells with an allogeneic B cell line in Th1-or Th2-biasing cytokine conditions. The populations were further enriched by using the Cytokine Secretion Assay to sort IFNc-or IL-5producing cells, respectively. The resulting populations were strongly polarized, but unlike mouse T cells, both Th1 and Th2 human cell lines expressed AR ( Figure 5A ).