Proliferation enhances P-lig expression on activated CD4⁺ lymphocytes. Naive CD4⁺ T cells from DO11.10 mice were CFSE labeled and stimulated with OVA_323-339 peptide and APCs plus IL-12, IFN-γ, and αIL-4. On day 3, individual generations (arrows, nos.) of undivided and divided KJ1-26.1⁺ cells were identified by loss of CFSE staining. (A) An example of control and P-lig staining in combination with CFSE. (B) The frequency of P-lig–positive cells within indicated generations of KJ1-26.1⁺ cells is summarized from 7 independent experiments (*P < .05).