No abstract

The pathogenesis of heat-induced cell death is controversial. Categorizing the death occurring after various heat loads as either apoptosis or necrosis might help to elucidate this problem, since it has been shown that these two processes differ in their mode of initiation as well as in their morphological and biochemical features. Log-phase cultures of mastocytoma P-815 x 2.1 were heated at temperatures ranging from 42 to 47 degrees C for 30 min. After 42 degrees C heating a slight increase in apoptosis was observed morphologically. However, after heating at 43, 43.5 and 44 degrees C, there was marked enhancement of apoptosis, and electrophoresis of DNA showed characteristic internucleosomal cleavage. With heating at 45 degrees C both apoptosis and necrosis were enhanced, whereas at 46 and 47 degrees C only necrosis was produced. DNA extracted from the 46 and 47 degrees C cultures showed virtually no degradation, which contrasts with the random DNA breakdown observed in necrosis produced by other types of injury; lysosomal enzymes released during heat-induced necrosis may be inactivated at the higher temperatures. It is suggested that apoptosis following heating may be triggered either by a limited increase in cytosolic calcium levels resulting from mild membrane changes or by DNA damage. Necrosis, on the other hand, is likely to be a consequence of severe membrane disruption.

Summary When B‐cell lymphocytic leukaemia (B‐CLL) cells derived from peripheral blood were cultured in vitro, a substantial proportion of them spontaneously died by apoptosis. This type of cell death is morphologically and biochemically distinct from necrosis and has previously been found to occur under physiologic and certain pathologic conditions where cell deletion appears controlled and biologically meaningful. By 30 h of culture, approximately 20% of the unfractionated B‐CLL cells were affected. There was no significant difference in the incidence of apoptosis in T‐cell depleted and undepleted cultures or when either autologous or normal human serum was used. Furthermore, seeding densities of 2 × 106 and 5 × 105 cells/ml resulted in a similar incidence of apoptosis, indicating that cell density was unlikely to be a contributing factor in producing the death. The finding that B‐CLL cells spontaneously die in vitro has at least two important implications. Firstly, previous work relating to some of the functions of B‐CLL cells and their interactions with T cells may require re‐evaluation. Secondly, an understanding of the mechanisms involved in the induction of apoptosis in this disease may have therapeutic consequences.

Savage NW, Mahanonda R, Seymour GJ, Bryson GJ, Collins RJ. The proportion of suppressor-inducer T-lymphoeytes is reduced in recurrent aphthous stomatitis. J Oral Pathol 1988: 17: 293-297. A flow cytometric analysis of peripheral blood lymphocytes was undertaken in recurrent aphthous stomatitis patients. The project aimed at detecting differences within lymphocyte subsets using type-specific monoclonal antibodies. Peripheral blood samples were taken from RAS patients in both active and remission phases of the disease and from a group of healthy control subjeets. There were no statistical differences between the active and remission phases within any of the lymphoeyte subsets examined. There was, however, a significant difference between the RAS group and the control group. RAS patients have depressed CD4+ cell numbers and elevated CD8+ cell numbers. The CD4: CD8 ratio is also depressed. A dissection of the CD4+ subset shows raised numbers of CD4+, 4B4+ lymphocytes and depressed numbers of CD4+, 2H4+ lymphocytes. Previous studies have shown disruption of peripheral blood lymphocyte numbers in Behcets syndrome. A similar pattern has now been shown in uncomplicated cases of minor RAS.

Summary A number of reports indicate that protein synthesis is a requirement for the occurrence of apoptosis. In this study, the effect of the protein synthesis inhibitor cycloheximide (CHM) on spontaneous apoptosis of B-chronic lymphocytic leukaemia (B-CLL) cells, previously shown to occur when they are cultured in RPMI-1640 medium with autologous or heterologous serum, was examined. No definite inhibition of apoptosis was observed. Indeed, CHM-treatment augmented apoptosis in the B-CLL cultures and also induced apoptosis of cultured normal peripheral blood lymphocytes. Augmentation was dose-dependent for B-CLL cells over the concentration range 106 M (0.28 yig ml-') to 102 M (2800 yg ml-'), resulting in 9% to 98% apoptosis respectively by 24 h of culture (r = 0.619, P = 0.0008). Normal lymphocytes were affected by CHM over the range 10-4 M to 10-2 M, resulting in 7% to 74% apoptosis respectively (r = 0.794, P = 0.0001). Inhibition of protein synthesis in these cells by CHM was virtually complete at a concentration of 10-3 M. The findings are in accord with some recent reports indicating that suppression of protein synthesis by CHM does not inhibit apoptosis in all circumstances. They also illustrate the marked susceptibility of B-CLL cells, compared with normal lymphocytes, to the induction of apoptosis by this drug. The manner in which CHM triggers apoptosis of some cell types is at present uncertain.