PROGESTERONE MODULATES IFN-gamma SECRETION BY PERIPHERAL BLOOD NK CELLS INDEPENDENTLY FROM ITS APOPTOSIS INDUCING CAPACITY

L. ARRUVITO,; M. BARBOZA; M. SANZ; L. FAINBOIM

Brazil, Angra dos Reis

Simposio; The 6th International Cell Death Symposium on “The mechanisms of cell death in cancer and aging”. International Cell Death Society.; 2006

  Two subsets of Natural Killer (NK) cells are present in the peripheral blood (PBNK). The CD56dimCD16+ cytotoxic subset represent almost 90% of PBNK and the remaining 10% have the subset CD56brightCD16-, which secrete large amounts of IFN-g. Progesterone (Pr) is usually postulated as an immunosuppressor agent, although little is know about the way Pr suppress immune response. In this study, we focus on the effect of Pr on NK cells. Purified PBNK (by immunomagnetic negative selection) cultured for 48hs with Pr, suffered a significant dose dependent cell death (mean±SEM 31.13±1.74, 21±0.894, 14.75± 0.95 for 1x10-6M, 1x10-7M, 1x10-8M respectively). The apoptotic effect observed after 48 or 72hs of culture with Pr was blocked by the addition of the antagonists ZK 98.299 (1x10-5M and 1x10-6M) and RU 486 (1x10-7M), P<0.002. Both antiprogestins are also glucocorticoid (GC) antagonists. RU 486 shows a higher affinity for the GC receptor that for the Pr receptor (PR) and might represent a better antagonist. Confirming this hypothesis, we found that RU 486 and ZK 98.299 were able to diminish the apoptosis induced by either Pr or dexamethasone (Dex), but only ZK 98.299 was able to block the Pr-induced apoptosis, with little effect on Dex-induced apoptosis. Progesterone delivers inhibitory signals through a caspase-dependent pathway. Although caspase-3, 8 and 9 inhibitors (10uM or 50 uM) were able to block the Pr-induced apoptosis, caspase-9 inhibitor showed the highest apoptosis inhibition, P<0.028. IL-15 and IL-12 are known to induce the growth and IFN-g secretion of NK cells respectively. We demonstrated that addition of IL-15 and IL-12 was able to abrogate the Pr-induced apoptosis. However, the co-culture of IL-12-activated NK cells with Pr significantly reduced the secretion of IFN-g by these cells. Our findings identify two mechanisms by which Pr could alter the role of NK cells along immune response. One is the induction of a time and dose dependent apoptosis and secondly the induced inhibition of IFN-g secretion, the NK cell main effector cytokine.