INVOLVEMENT OF THE OMENTAL LYMPHOID ORGAN IN THE INDUCTION OF PERITONEAL IMMUNITY AGAINST TUMOR-CELLS

The omental lymphoid organ (OLO) is a part of the greater omentum comp osed of vascularized spots containing lymphocytes, plasma cells and ma crophages located in a regular pattern between fat cells. To gain insi ght in the involvement of the OLO in the induction of immunity against tumor cells in the peritoneal cavity, we studied the penetration of t umor cells into the OLO after intraperitoneal, subcutaneous and intrav enous injection. Furthermore we analyzed the tumoricidal activity of m acrophages isolated from the OLO. Our results indicate that the OLO is only infiltrated by tumor cells directly from the peritoneal cavity, but not by subcutaneously or intravenously injected tumor cells unless they have reached the peritoneal cavity. Bromodeoxy-uridine labelled tumor cells can be detected in the OLO within 10 min after i.p. inject ion. The penetration is facilitated by the induction of fenestrations between the mesothelial cells (lining the OLO) after intraperitoneal i njection of the tumor cells. These fenestrations can also be seen afte r nonspecific stimulation of the peritoneal cavity. Macrophages isolat ed from the OLO of mice immunized against syngeneic as well as allogen eic tumor cells express a significant cytotoxicity, which (at least in the syngeneic situation) precedes the cytotoxicity of the macrophages isolated from the peritoneal cavity. In conclusion, our data support the hypothesis that immune reactions against intraperitoneally injecte d tumor cells are initiated in the OLO leading to 'peritoneal immunity ' against these tumor cells.