Immunohistochemistry. Immunohistochemistry was performed with monoclonal antibodies against CD1c (L161, Abd Serotec, Oxford, UK) and CD1d (NOR3.2, Abcam, Cambridge, UK) (both 1:100) on frozen cHL tissue sections and cytospins using standard laboratory protocols and appropriate positive and negative controls. Cases were defined positive when more than 50% of tumor cells showed a clear staining.