TUMOR-NECROSIS-FACTOR-ALPHA AND INTERFERON-GAMMA MODULATION OF NITRIC-OXIDE AND ALLOGRAFT SURVIVAL

Tumor necrosis factor-alpha (TNF) and interferon-gamma (IFN) modulate immune responses, as TNF is postulated as a first messenger for primin g immune cells and IFN as the second messenger for activation. Nitric oxide (NO) is also an important mediator of immune function, as NO pro duced by immune cells in response to cytokines such as TNF and IPN may be a cytotoxic end-product effector of immune activation. To examine TNF and IFN modulation of NO production and effects upon allograft sur vival, we studied the in vitro effect of TNF, IFN, and lipopolysacchar ide (LPS, as a nonspecific immune stimulator and TNF promoter) singly or together on NO production in unstimulated rat splenocytes or in res ponse to allogeneic stimulation in MHC mismatch (Brown-Norway, BN, vs Lewis, LEW) mixed lymphocyte reactions. Nitrite as a stable reaction p roduct of NO was determined by a colorimetric method based on the Grie ss reaction. Interestingly, unstimulated cells had little NO productio n in response to TNF or IFN; however, following nonspecific (LPS) or a llegeneic stimulation there was a significant upregulation of NO produ ction that was synergistically enhanced by the presence of both TNF an d IFN. Significantly, anti-TNF antibody inhibited NO production up to 60% in all groups. lie vivo studies used a cardiac heterotopic allotra nsplant model, again BN to LEW. Control recipients received no immunot herapy. Experimental recipients received IFN alone, anti-IFN antibody, anti-TNF antibody, or anti-TNF and anti-IFN antibody. Results from th ese allograft experiments showed no influence on survival by IFN alone or anti-IPN antibody alone. However, anti-TNF antibody extended allog raft survival, which was synergistically and significantly enhanced wi th the addition of anti-IFN antibody. These results demonstrate that c ytokines synergistically modulate immune response via NO synthesis, as NO is markedly increased by IFN in the presence of allogeneic stimula tion or TNF/LPS. Furthermore, as anti-IFN was only beneficial to allog raft survival in the presence of anti-TNF, the priming and activating roles of these cytokines in modulating the alloimmune response via NO production suggest that transplant rejection may be mediated through a distinct cascade. Modulation of cytokine-NO cascades may lead to new therapies. (C) 1995 Academic Press, Inc.