Expression of regulatory T-cell markers by CD4⁺ lymphocytes. (A) Expression of CTLA-4, OX40, or GITR by CD4⁺ T cells from adult or cord blood, spleen, or lymph nodes. Cells were stained for intracellular expression of CTLA-4 and surface expression of OX40 and GITR, together with CD4 and CD25. Profiles are gated for lymphocytes expressing CD4. (B) Expression of HLA-DR, CD71, CD38, CD62L, CCR7, CD27, CD45RA, CD45RO, CD58, CD95, and CD44 by adult peripheral-blood cells costained for CD4 and CD25. Profiles are gated for live cells expressing CD4. The circled populations in the CD45RA, CD45RO, CD58, and CD95 plots represent a second population of CD25⁺ T cells distinguishable from the CD25^bright population. In the CD44 profile, 2 distinct populations of CD25⁺ T cells are identified using parallelograms. Results are representative of between 3 and 9 independent experiments for each sample and stain.