Immunosuppression by hyperbaric oxygen.

Reports from several laboratories have indicated that hyperbaric oxygen might be immunosuppressive in animals. We examined the effect of hyperbaric oxygen on a well-studied model of cell-mediated immunity in the mouse, contact sensitivity to dinitrofluorobenzene (DNFB). Using this model, we showed that daily 5-hour exposure of mice to 2.5 ATA hyperbaric oxygen was markedly immunosuppressive. Immunosuppression occurred when mice were exposed to hyperbaric oxygen (HBOX) for 4 days daily before DNFB sensitization or for 5 days daily after sensitization. The immunosuppression was reversed by intravenous administration of 2 x 10(7) peritoneal exudate cells from syngeneic mice, but was not reversed by 5 x 10(7) lymph node cells intravenously. We showed that daily HBOX exposure resulted in a dramatic decrease in circulating total leukocytes and lymphocytes in spleen weight, and in DNA synthesis in draining lymph nodes of sensitized mice. Serum cortisol levels were only marginally elevated in HBOX-treated mice.