Administration of OKT3 anti-CD3 monoclonal antibody (mAb) to patients for transplant rejection, is associated with a distinct and often severe clinical syndrome related to massive cytokine release. Previous reports have similarly demonstrated increased levels of serum tumor necrosis factorα(TNFα) in normal mice following administration of 1452-C11 anti-CD3 mAb. In this study, we compared serum TNFαlevels at baseline and after anti-CD3 stimulation among three groups of mice: normal BALB/c controls, pre-diabetic non-obese diabetic (NOD) mice, and diabetic NOD mice. Baseline serum TNFαlevels, as measured by L929 cell bioassay, were 2×higher in diabetic NOD and 3×higher in pre-diabetic NOD compared with BALB/c. Ninety minutes after anti-CD3 mAb stimulation, serum from BALB/c controls and pre-diabetic NOD contained 2-to 8-fold higher levels of TNF-αas compared to untreated control mice. In contrast, following anti-CD3 mAb, there was a dramatic 20-fold increase in serum TNFαin diabetic NOD mice (levels>5000 pg/ml). Additionally, anti-CD3 mAb increased the steady-state TNFαmRNA transcripts. Spleens from diabetic mice given anti-CD3 mAb had higher steady-state TNFαmRNA than spleen from normal mice similarly treated. The enhanced release of circulating TNFαafter anti-CD3 mAb in diabetic NOD mice was abrogated by pre-treatment of mice with prostaglandin E1(PGE1) 30 min prior to anti-CD3 mAb stimulation. Since dietary lipid can influence cytokine generation, serum from BALB/c mice fed fish (FO) or safflower oil (SO) supplemented diets was examined for TNFαbefore and after administration of anti-CD3 mAb. Mice supplemented with a FO diet had higher serum TNFαlevels at baseline and following anti-CD3 mAB compared with mice fed SO. Supplementation of either lipid resulted in higher serum TNFαlevels than mice fed standard laboratory chow (LC) (4.5% lipid). Taken together, we suggest the enhanced capacity of OKT3 to induce TNFαin patients with IDDM can be diminished by injection of PGE1. In addition, clearly the amount and composition of dietary lipid should be regulated in patients with IDDM receiving anti-CD3 mAb therapy.