Comparison of regulatory cell marker expression in healthy donor PBMCs and HL patient PBMCs, and HLILs. Staining for representative examples of healthy donor PBMCs (n = 4) and HL patient PBMCs (n = 9) and HLILs (n = 6). Plots show the percentage of lymphocytes staining positive for CD4 and IL-10, or CD4 and CD25, or the percentage of CD4⁺ lymphocytes staining positive for the costimulatory molecule CTLA-4. Cells were stained within 24 hours of purification and were unstimulated prior to staining. The control staining plots show the percentage of lymphocytes staining positive for CD4 and isotype control antibodies.