Heat-Shocked A20 Lymphoma Cells Fail to Induce Degranulation of Cytotoxic T Lymphocytes: Possible Mechanism of Resistance

A20 lymphoma cells were subjected to heat shock for 2 h at 42 and 43 ± 0.1°C and then evaluated at 37°C for sensitivity to lysis by intact allo-specific cytotoxic T lymphocytes (CTLs), perforin-containing granules isolated from CTLs, and Fas-mediated apoptosis. Heat shock at 42°C caused little change in sensitivity of the lymphoma cell line to lysis by intact CTLs or their isolated cytotoxic granules, but caused increased sensitivity to Fas-mediated apoptosis. However, A20 cells shocked at 43°C declined significantly in sensitivity to lysis by intact CTLs, while remaining very sensitive to perforin granules and to Fas-mediated apoptosis. Expression of the inducible heat shock protein was observed in A20 cells incubated at 43°C, but not in those incubated at 42°C, suggesting a role for heat shock proteins. Furthermore, A20 cells shocked at 43°C did not provoke degranulation and secretion of granzymes by antigen-specific CTLs, although formation of CTL-target conjugates and levels of MHC class I molecules remained unchanged. These observations demonstrate that hyperthermia or febrile conditions may reduce susceptibility of target cells to CTL attack due to failure of antigen presentation and the inability of CTLs to recognize heat stressed targets, thus enabling targets to escape CTL attack.