Subsets of murine CD4⁺ T cells localize to different areas of the spleen after adoptive transfer. Naı̈ve and T helper 1 (T_H1) cells, which express the chemokine receptor CCR7, are home to the periarteriolar lymphoid sheath, whereas activated T_H2 cells, which lack CCR7, form rings at the periphery of the T cell zones near B cell follicles. Retroviral transduction of T_H2 cells with CCR7 forces them to localize in a T_H1-like pattern and inhibits their participation in B cell help in vivo but not in vitro. Thus, differential expression of chemokine receptors results in unique cellular migration patterns that are important for effective immune responses.