It has recently been reported that combination immunotherapy utilizing cyclosporin A (CsA) and prostaglandin E (PGE) reduced the frequency of acute renal allograft rejection; however, the mechanism for the benefit of this combination therapy is uncertain. Since our previous studies have suggested that macrophage procoagulant activity (PCA) is an important mediator of allograft rejection, in this study we have examined the effects of CsA and 16,16 dimethyl prostaglandin E2 (dmPGE2) alone and in combination on the induction of macrophage PCA and on the lymphokines macrophage procoagulant-inducing factor (MPIF) and interleukin-2 (IL-2) in vitro. Alloantigen-induced MPIF activity could be detected within 8 hr, reaching maximal levels by 12 hr and could still be detected at 24 hr. Allogeneic induction of PCA in splenic mononuclear cells was detectable by 24 hr, reaching maximal levels at 72 hr and was still detectable after 120 hr. CsA at concentrations from 100 ng/ml to 1000 ng/ml completely inhibited production of MPIF and IL-2, but had minimal effects on the ability of MPIF to induce isolated macrophage to express PCA. In contrast, dmPGE2 (10(-12)-10(-6) M) inhibited both the induction of MPIF and the ability of MPIF directly to induce macrophages to express PCA, with lesser effects on the induction of IL-2. The effects of minimal inhibitory concentrations of CsA and dmPGE2 in combination resulted in synergistic inhibition of PCA induction. These data demonstrate the disparate actions of CsA and dmPGE2 on inhibition of PCA, MPIF and IL-2, and provide a possible mechanism for the beneficial effects of combination CsA and dmPGE2 in patients receiving organ allografts.