We examined the role of cyclooxygenase-2 (COX-2) in the late phase of ischemic preconditioning (PC). A total of 176 conscious rabbits were used. Ischemic PC (six cycles of 4-min coronary occlusions͞4-min reperfusions) resulted in a rapid increase in myocardial COX-2 mRNA levels (؉231 ؎ 64% at 1 h; RNase protection assay) followed 24 h later by an increase in COX-2 protein expression (؉216 ؎ 79%; Western blotting) and in the myocardial content of prostaglandin (PG)E2 and 6-keto-PGF1␣ (؉250 ؎ 85% and ؉259 ؎ 107%, respectively; enzyme immunoassay). Administration of two unrelated COX-2 selective inhibitors (NS-398 and celecoxib) 24 h after ischemic PC abolished the ischemic PC-induced increase in tissue levels of PGE2 and 6-keto-PGF1␣. The same doses of NS-398 and celecoxib, given 24 h after ischemic PC, completely blocked the cardioprotective effects of late PC against both myocardial stunning and myocardial infarction, indicating that COX-2 activity is necessary for this phenomenon to occur. Neither NS-398 nor celecoxib lowered PGE 2 or 6-keto-PGF1␣ levels in the nonischemic region of preconditioned rabbits, indicating that constitutive COX-1 activity was unaffected. Taken together, these results demonstrate that, in conscious rabbits, up-regulation of COX-2 plays an essential role in the cardioprotection afforded by the late phase of ischemic PC. Therefore, this study identifies COX-2 as a cardioprotective protein. The analysis of arachidonic acid metabolites strongly points to PGE 2 and͞or PGI2 as the likely effectors of COX-2-dependent protection. The recognition that COX-2 mediates the antistunning and antiinfarct effects of late PC impels a reassessment of current views regarding this enzyme, which is generally regarded as detrimental.

Impaired immunity in late stage cancer patients is not limited to anti-tumor responses, as demonstrated by poor vaccination protection and high susceptibility to infection 1 – 3 . This has been largely attributed to chemotherapy-induced impairment of innate immunity such as neutropenia 2 , whereas systemic effects of tumors on hematopoiesis and adoptive immunity remain incompletely understood. Here we observed anemia associated with severe deficiency of CD8 + T cell responses against pathogens in treatment-naïve mice bearing large tumors. Specifically, we identify CD45 + erythroid progenitor cells (CD71 + TER119 + , EPCs) as robust immunosuppressors. CD45 + EPCs, induced by tumor growth-associated extramedullary hematopoiesis, accumulate in the spleen to become a major population, outnumbering regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). The CD45 + EPC transcriptome closely resembles that of MDSCs, and, like MDSCs, reactive oxygen species production is a major mechanism underlying CD45 + EPC-mediated immunosuppression. Similarly, an immunosuppressive CD45 + EPC population was detected in cancer patients with anemia. These findings identify a major population of immunosuppressive cells that likely contributes to the impaired T cell responses commonly observed in advanced cancer patients.