CD1c was undetectable in cHL cell lines L428, KMH2, L1236, and U-HO1 (data not shown). In tonsil tissue, CD1c stained positive in the mantle zone (MZ) and predominantly negative in the germinal centers (GC) of secondary lymphoid follicles (Fig. 1A) consistent with the previously reported expression pattern [11] . HRS cells in cHL were consistently CD1c negative in all cases (Fig. 1B) , whereas 14 out of 39 non-Hodgkin lymphomas (NHL) were positive (Table I) . The absence of CD1c expression in both GC B cells and HRS cells is consistent with the current assumption that HRS cells are derived from GC B cells [12] . CD1c expression has been reported in some other B-cell NHL subtypes, including GC B cell derived follicular lymphoma [11] . In B-cell NHL, an inverse correlation was noticed between CD1c and the proliferative activity assessed by expression of Ki-67 [11] . This is in line with the lack of CD1c staining in GC B cells that show a high proliferation index and high CD1c expression in the MZ B cells that are in a resting state. Ki-67 was shown to be highly expressed in HRS cells [13] correlating with the lack of CD1c expression. CD1c expression was found in reactive cells in all cases with a percentage varying from a few to the vast majority, similar to the CD1c expression pattern observed in interfollicular regions of tonsil tissue.