The present invention relates to regulation of lymphocyte activation. More particularly, the present invention is directed to nucleic acids encoding PAK2, which is involved in modulation of lymphocyte activation. The invention further relates to methods for identifying and using agents, including small organic molecules, peptides, circular peptides, antibodies, lipids, antisense nucleic acids, and ribozymes, that modulate lymphocyte activation via modulation of PAK2; as well as to the use of expression profiles and compositions in diagnosis and therapy related to lymphocyte activation and suppression.