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Altered macrophage function after thermal injury is associated with increased production of PGE2 and TNF. However, it is not clear why synthesis of both cellular products remains elevated, as PGE2 is a potent inhibitor of TNF secretion. We studied the relationship between PGE2 and TNF synthesis in a murine model of thermal injury, and examined the effect of prostaglandin blockade on splenic macrophage secretion of these mediators of inflammation. LPS-stimulated production of PGE2 was significantly elevated in burn groups compared with sham-burned controls (pg/ml mean(SEM); sham 151(32): burn 597(147), p < 0.01). TNF production was similarly increased after thermal injury (pg/ml mean(SEM); sham 62(20): burn 928(316), p < 0.01). In vitro culture of macrophages with indomethacin augmented LPS stimulated TNF production in sham-burned controls but did not affect synthesis in burn groups, suggesting a loss of PGE2-dependent regulation of TNF synthesis after thermal injury. Direct measurement of TNF secretion as a function of exogenous PGE2 confirmed this dissociation between PGE2 and TNF synthesis, as burned animals displayed a 5-fold reduction in sensitivity to PGE2-induced inhibition of TNF, when compared with sham-burned controls (ID50 PGE2 molar; sham 1.26 x 10(-8): burn 6.43 x 10(-8), p < 0.05). In vivo pretreatment of burn groups with indomethacin for 5 days before assay partially restored sensitivity to the prostaglandin, and significantly down-regulated synthesis of both TNF and PGE2. These data show that thermal injury is associated with a loss of PGE2-dependent down-regulation of TNF synthesis, which accounts at least in part for increased TNF in these animals. In vivo cyclooxygenase blockade partially restored sensitivity to the prostaglandin and consequently down-regulated synthesis of TNF. These data further support existing evidence that suggests a potential therapeutic role for cyclooxygenase blockade after major thermal injury and trauma.

The purpose of the present study was the investigation of the effect of cyclosporin A (CsA) on the induction of alloreactivity in vitro and in vivo. Addition of CsA to mouse mixed lymphocyte cultures (MLC) not only inhibited lymphocyte proliferation but also prevented the generation of alloreactive cytolytic lymphocytes (CL). It was necessary to add CsA within the first 3 days of a 5-day MLC in order to achieve a significant suppressive effect. Lymphocytes, after being cultured in MLC with CsA for 4 days or longer, were incapable of being activated upon re-exposure to the same alloantigens although their responses to unrelated antigens remained intact, indicating antigen specificity of the suppression induced by CsA and its long-lasting effect. Furthermore, lymphocytes from mice treated with CsA after allosensitization failed to manifest primary cytotoxicity and could not be reactivated in a secondary MLC. Finally, CsA had no effect on those CL already generated, suggesting that CsA acts upon the induction of CL rather than the effector phase.

Mice sensitized with alloantigens and treated with cyclosporin A (CsA) were incapable of generating antigen-specific cytolytic lymphocytes (CL). Lymphocytes from these CsA-treated animals could not be reactivated upon exposure to the same alloantigens in mixed lymphocyte culture (MLC), whereas their response to a third-party antigen remained intact, suggesting a long-lasting and specific effect of CsA. After being irradiated, these lymphocytes from CsA-treated animals were added to normal MLC and were shown to prevent normal lymphocytes from becoming cytolytic in a dose-dependent and antigen-nonspecific fashion. These suppressor cells were not detected in mice receiving CsA only, indicating that CsA did not induce but rather permitted the expression of suppressor cells possibly generated by allosensitization. The suppressor cells appeared to be T lymphocytes, because treatment with anti-Thy-1.2 antibody and C abrogated their suppressive activity. The present results suggest that activation and/or sparing of suppressor cells by CsA may account for the long-lasting unresponsiveness seen in CsA-treated animals.

There exists in the serum α-globulins an immunosuppressive factor(s) which was first described by Kamrin (1), and subsequently separated chromatographically by Mowbray (2), and by our laboratories (3, 4). This factor has been demonstrated to prolong skin grafts (3) and to inhibit antibody formation (5, 6). We have also found that this factor inhibits lymphocyte proliferation induced in vitro by both mitogens and antigens (4). We have recently found that the active factor is a polypeptide(s) which migrates electrophoretically with, and may be bound to, an α-globulin protein(s) (7). We have called the active material “immunoregulatory α-globulin” (IRA).4 The mechanism of action of this immunosuppressive factor remains to be determined. Studying mitogen stimulation of lymphocytes in tissue culture, we have observed that the IRA is not suppressive if this agent is added after the lymphocytes have become activated (8). This observation suggests that the IRA acts upon the early events involved in antigen recognition.