, . 185: 116 (1998) LETTER TO THE EDITOR MUMMIFIED HODGKIN CELLS AND APOPTOSIS The study by Lorenzen et al.1 is worthy of note, since the mummified cells of Hodgkin’s disease (HD) have long remained an enigma, being loosely considered as degenerating Hodgkin–Reed–Sternberg (HRS) cells. In our studies on cell death in HD,2,3 we have reached conclusions about mummy cells which are similar to those of the authors. We found that mummy cells did not show DNA fragmentation (by the ApopTag assay). However, although the electron microscopic (EM) features of these cells were similar to those found by Lorenzen et al.,1 we were impressed by the swollen mitochondria which imparted to these cells the appearance of ‘dark cells’. Nonetheless, we agree with the authors on the significance of this phenomenon. We are dealing with irreversibly damaged cells, probably showing an atypical form of apoptosis, perhaps para-apoptosis. On the other hand, we were able to demonstrate apoptotic cells which were strongly reactive by in situ end labelling of DNA fragments. These cells were interpreted as apoptotic HRS cells, based on their size, on their positivity by CD15 immunostaining, and most importantly, on their EM features. The discrepancy noted may be due to the different methods used, including fixation. In our hands, DNA is less well preserved in picric acid-based fixatives. D B1, P B2, J G1 J G3 1 Department of Pathology Soroka Medical Center, Beer-Sheva, Israel 2 Laboratory of Pathology, Hopital Purpan, Toulouse, France 3 Department of Oncology Soroka Medical Center, Beer-Sheva, Israel REFERENCES 1. 2. 3. Lorenzen J, Thiele J, Fischer R. The mummified Hodgkin cell: cell death in Hodgkin’s disease. J Pathol 1997; 182: 288–298. Benharroch D, Prinsloo I, Goldstein J, et al. A comparison of distinct modes of tumor cell death in Hodgkin’s disease using morphology and in situ DNA fragmentation. Ultrastruct Pathol 1996; 20: 497–505. Brousset P, Benharroch D, Krajewski S, et al. Frequent expression of the cell death-inducing gene Bax in Reed–Sternberg cells of Hodgkin’s disease. Blood 1996; 87: 2470–2475. AUTHORS’ REPLY We should like to thank D. Benharroch et al. for their comments on our paper and for drawing our attention to their publication in Ultrastructural Pathology.1 It was reassuring to find similar conclusions being drawn from the ultrastructure and the absence of an ISEL reaction of mummified Hodgkin- and Reed–Sternberg (HRS) cells by an independent research group. As pointed out in our manuscript,2 we have also noticed a few larger cells that displayed a weak and more diffuse in situ end-labelling reaction in nuclei that had lost chromatin detail. These cells were occasionally found within the cytoplasm of macrophages reacting with the monoclonal antibody PG-M1. Although the size of this cell population suggests that it is derived from the HRS cells, we found no hard evidence for this assumption, as cytological features were lost and no immunoreaction for CD15 or CD30 could be observed in our hands. This discrepancy may indeed be due to different immunohistochemical methods applied, even though no picric acid-based fixatives are used in our laboratory. Furthermore, we are not convinced that these mysterious cells are truly apoptotic, because they do not display the typical crescent-shaped chromatin condensation on electron microscopic examination or in semi-thin sections. Whereas we do not dispute that DNA degradation will take place at some stage during the removal of mummified HRS cells from the tissue, and hence might be detected by the in situ end-labelling techniques, we have reservations about the internucleosomal nature of the ensuing DNS strand breaks. In contrast to apoptotic bystander cells, the cell popu 1998 John Wiley & Sons, Ltd. lation in question displays a weaker and more diffuse nuclear ISEL reaction. Considering our experimental findings, we thus cannot prove that the larger cells labelled in the ISEL reaction are derived from HRS cells and that they fulfill all of the criteria required for classical apoptosis. It might well be the case that differences in the laboratory protocols for the detection of DNA strand breaks have led us to different conclusions. In this context, two articles by Spina and co-workers are worth mentioning, as this group describes the presence of DNA strand breaks in the majority of HRS cells.3,4 Hence, the books on cell death in Hodgkin’s disease are not yet closed. J L, J T R F Department of Pathology University of Cologne Joseph-Stelzmann-Strasse 9 50931 Koeln, Germany REFERENCES 1. 2. 3. 4. Benharroch D, Prinsloo I, Goldstein J, Brousset P, Kachko L, Gopas J. A comparison of distinct modes of tumor cell death in Hodgkin’s disease using morphology and in situ DNA fragmentation. Ultrastruct Pathol 1996; 20: 497–505. Lorenzen J, Thiele J, Fischer R. The mummified Hodgkin cell: cell death in Hodgkin’s disease. J Pathol 1997; 182: 288–298. Spina D, Leoncini L, Close P, et al. Growth vs. DNA strand breaks in Hodgkin’s disease: impaired proliferative ability of Hodgkin and Reed–Sternberg cells. Int J Cancer 1996; 66: 179–183. Leoncini L, Spina D, Close P, et al. Abortive mitoses and nuclear DNA fragmentation in CD30+ large cells of Hodgkin’s disease. Leuk Lymphoma 1996; 22: 119–124.