Heat-induced unresponsiveness of heat shock gene expression is regulated at the transcriptional level.

The induction kinetics of the heat shock proteins hsp68, hsp70 and hsp84 were studied. Studies on hsp mRNA levels and protein synthetic rates, with or without the presence of actinomycin D, showed that regulation took place at the transcriptional level. Hsp mRNA induction was followed by a transient state of unresponsiveness. At the time point where the induced hsp mRNAs were decreasing again, hsp68, hsp70 and hsp84 mRNA could not be induced by a second, identical, heat shock. Hsp68 mRNA could be induced again 12-16 h after the first heat shock. Apparently, this state really seems to be a state of reduced sensitivity, since a higher heat dose could partially overcome this unresponsiveness.

Parathymic lymph nodes during growth and rejection of intraperitoneally inoculated tumor cells.

The omental lymphoid organ (OLO) is a part of the greater omentum composed of vascularized milky spots situated between fat cells and containing lymphocytes, plasma cells and macrophages. We analysed the disappearance of intraperitoneally injected tumor cells from the peritoneal cavity and their infiltration into and disappearance from the OLO and the parathymic lymph nodes (PTLN) that drain the peritoneal cavity. After intraperitoneal inoculation of irradiated syngeneic tumor cells, they were visible in the OLO within 24 h. After 3 days, no tumor cells were seen anymore, but there were many macrophages that had phagocytosed tumor cells. After intraperitoneal inoculation of nonirradiated syngeneic tumor cells, a solid growing tumor mass developed in the OLO. The PTLN were also invaded by these nonirradiated tumor cells within 24 h as transfer of cell suspensions of these lymph nodes into naive mice leads to the death of the recipient mice due to tumor growth. However, from day 6 onwards, after tumor inoculation, these lymph nodes contained no tumor cells, despite progressive tumor growth intraperitoneally and in the liver and lungs. In allogeneic mice, tumor cells were rejected in the OLO after 7-10 days. Simultaneously, the number of lymphocytes and macrophages increased and a plasma cell reaction developed. The PTLN did not have tumor-inducing potency at any stage after intraperitoneal tumor injection. This study suggests, that the PTLN are more effective in the (local) eradication of tumor cells than the OLO. Still, considering its immunological potential, the OLO might be important as 'inducer' of immunological reactions in the peritoneal cavity.